A235—423—15M—L TEXAS AGRIEUETIJ I EXPERIMENT STATIIIN AGRICEULTURALAND MECHANICAL COLLEGE OF TEXAS W. B. BIZAZELL, President BULLETIN NO. 307 I APRIL, I923 DIVISION OF PLANT PATHOLOGY AND PHYSIOLOGY TEXEASE Rom ROT OF COTTON AND METHODS OF ITS CONTROL ._',-*' AGRICULTURAL & > LLEGE 0F é*Aé§ B. YOUNGBLOOD, DIRECTOR, COLLEGE STATION, BBAZOS COUNTY, TEXAS STATION STAFF? A DMINISTRATION B YOUNGBLOOD. M. S , Ph. D., Director A. B. CoNNER, B. S., Vice Director, and Chief Division 0f Agronomy _ CHARLES A. FELKER. Chief Clerk A. S. WARE, Secretary _ A. D. JAcKsoN, Executive Assistant_ CRARLEs GORZYCKI, Technical Assistant M. P. lloLLEmAu. JR.. Assistant Chief Clerk R. N. BuRRows, M. A., Research Librarian VETERINARY SCIENCE ‘M. FRANCIS, D. V. M., Chief _ l-l. SCHMIDT, D. V. S.. Veterinarian V. J. BRAUNER, D. V. M., Veterinarian CHEMISTRY G. S. FRAPs, Ph. D., Chief; State Chemist S. E. AsBURY, M. S., Assistant Chemist 1S. LOMANITZ, B. S., Assistant Chemist WALoo WALKER, Assistant Chemist W. C. MrrcHELL, B. S., Assistant Chemist A. G. PETERSON, B. S., Assistant Chemist HORTICULTURE H. NEss, M. S.. Chief W. S. HOTCHKISS, Horticulturist ANIMAL INDUSTRY J. M. JONEs, A. M., Chief R. M. Sherwood, B. S., Poultry Husbandman G R. WARREN, B ., Swine Husbandman J L. Lusir, Ph. D., Animal Husbandman (genetics) ENTOMOLOGY M. C TANQUARY, Ph. D., Chief: State Entomologist H. J. REINHARD, B. S., Entomologist H. B. PARKS, B. S., Apiculturist C. S. RUDE, B. S., Entomologist A H. ALEX. B. S., Queen Breeder W. O. VICTOR, JR., Apiary Inspector AGRONOMY A. B. CONNER, B. S.. Chief A. H. LEIDIGH, B. S., Agronomist E. B. REYNoLns, M. S., Ayronomist G. N. STROMAN, M. S., Agronomist; Farm Superintendent "PEARL DRUMMOND, Seed Analyst PLANT PATHOLOGY AND PHYSIOLOGY J. J. TAUBENHAUS, Ph. D., Chief COTTON BREEDING IG F. FREEMAN, D. Sc.. Chief (1)E. P. HUMBERT, Ph. D., Acting Chief H. E. REA, B. S., Plant Breeder FARM AND RANCH ECONOMICS L. P. GABBARD, M. S., Farm and Ranch Economist _ R. N. WADE, Laboratory Assistant FEED CONTROL SERVICE L. M. MURPRY, Wool and Mohair Specialist B, YOUNGBLOOD, S., Ph. D., Director J. D. SUNKEL, Dairyman D. FULLER, S . Chief Inspector .D. P . cE, n ector 5°15 SURVEY J. H. R2221“, Ingzector **W. T. CARTER, JR., B. S., Chief W. H. W000, Inspector H. W. HAWKER, Soil Surveyor J. J. KELLY, Inspector H. V. GEIB, B. S., Soil Surveyor SUBSTATIONS No. 1. Beeville, Bee County No. 8. Lubbock, Lubbock County l. E. CowART, M. S., Superintendent No. 2. Troup,‘ Smith County W. S. HOTCHKISS, Superintendent No. 3. Angleton, Brazoria County V. E. HAFNER, B. S., Superintendent No. 4. Beaumont, Jeflerson County A. H. PRmcE, B. S., Superintendent No. 5. Temple, Bell County D. T. KILLOUGR, B. S., Superintendent No. 6. Denton. Denton County P. B. DUNKLE, B. S., Superintendent No. 7- Spur, Dickens County R. E. DICKSON, B. S., Superintendent TAs of April 1, 1923. 10n leave. R. E. KARPER, B. S., Superintendent No. 9. Balmorhea, Reeves County J. J. BAYLEs, B. S., Superintendent No. l0. College Station, Brazos County (Feeding and Breeding Substatiom L. J. McCALL, Superintendent No. ll. Nacogdoches, Nacozdoches County G. T. McNEss, Superintendent **No. 12. Chillicothe, Hardeman County A. B. CRON, B. S., Superintendent No. 14. Sonora, Sutton-Edwards Countiel E. M. PETERs. B. S., Superintendent _ D. H. BENNETT, V. M. D., Veterinarian *In cooperation with School oi Veterinary Medicine, A. and M. College of Texas. ' "In cooperation with United States Department of Agriculture. (l) In cooperation with School of AgricultuieA. and NI. College of Texas. BULLETIN N0. 307 _ APRIL, 1923 TEXAS ROOT ROT OF COTTON AND METHODS OF ITS CONTROL BY J. J. TAUBENHAUS AND D. T. KILLOUGH. SUMMARY. 1. By reason of the large number of cultivated crops which it attacks, the Texas root rot disease is perhaps one of the most important of plant diseases in the State. 2. The same disease is equally serious in Arizona, and to a less extent in Oklahoma, New Mexico, and Southern California. 3. Texas root rot has been reported from sixty-seven counties in the ‘State with the probability that it is present in other counties. 4. With similar soil and climatic conditions (winter conditions especially), it is strange that Texas root rot is not apparently present in Louisiana, Mississippi, Alabama, and the many other Cotton States. Should the disease ever spread further than its present known dis- tribution, it may seriously threaten the cotton industry, the alfalfa, and the many other susceptible crops of the South. 5. The symptoms of the Texas root rot disease are the same or nearly the same on all susceptible hosts. 6. With cotton or other herbaceous crops, the Texas root rot begins to attract attention during July and August, reaching its height of destruction about September. - 7. Texas root rot spots are not always circular in shape as is popu- larly believed. 8. Texas root rotspreads underground from contact of infected roots of one plant with adjoining healthy ones of another. 9. From studies thus far, it might be stated that the Texas root rot disease is capable of attacking thirty-one difierent economic field crops, fifty-eight different truck crops, eighteen different kinds of fruit and berries, thirty-five different kinds of forest trees and shrubbery, seven different kinds of outdoor herbaceous ornamentals, and twenty different kinds of weeds. i 10. There seems to exist but slight difference in resistance in the various varieties of cotton. 11. Of the varieties of apples and pears tested none seemed to possess any resistance. 12. The peach seems to be highly resistant and the pecan appar-i ently wholly resistant to Texas root rot. The same, is true for all the grain and cereal crops. The guar, a newly-introduced legume, is highly resistant. 13. Cotton strains which seem to resist the disease longest during 4 BULLETIN N0. 307. the summer eventually become infected during the fall 0r Winter. Such strains, however, may be valuable and selected for partial re- sistance. 14.. There seems to be more root rot in cotton if this crop follows a more susceptible host, such as the sweet potato. 15. The factors which greatly influence the summer spread of root rot seem to be a wet season or irrigation, soil temperature, and a well-g developed root system, which favors underground contact. 16. Deep plowing as a method of controlling Texas rot has been exaggerated at the expense of more fundamental factors. 17. It is doubtful if the addition of humus or manure to the soil will greatly influence root rot control although it may increase the yield in cotton. 18. Early planting and close planting of susceptible hosts greatly influence the amount of Texas root rot during a favorable season, be- cause of a better contact of the roots underground. 19. Clean culture (not ordinary slipshod clean culture) may con- trol Texas root rot of cotton if it is based on a knowledge of the many winter carriers, and on the life history of the causal organism. 20. Crop rotation may control Texas root rot if clean culture is practiced and all winter carriers are destroyed. 21. Crop rotation has failed to control Texas root rot wherever absolute clean culture was not practiced, and where winter carriers were left unmolested during the fall and winter months. 22. We are, as yet, unable to predict with certainty the effect of various fertilizers or sulphur in controlling Texas root rot. This re- quires further testing for several more years. 23. A root-rot spot one year may not necessarily reappear the following year if a susceptible crop is grown in that field. The dis- appearance of the spot in that case may be due to the fact that the disease has killed out the winter carriers. 24. The Texas root rot disease is not caused by alkali in the soil. 25. For a long time, scientists suspected, through circumstantial evidence, that the cause of Texas root rot was a fungus, Phyma- totrichum omnirvorum (Shear) Duggar. 26. Through our modified methods, we have shown, by artificial inoculations, that Phymatotrichum omnivorum is the cause of the Texas root rot disease. 27. The causal organism is diflicult to isolate in pure culture. We have used and modified Atkinson's method with good results. 28. When the causal organism is once isolated in pure culture, it may be grown on any number of media. It grows poorly on sterilized soil. 29. Because of its peculiar structure, Phymatotrichum omnivorum may be readily distinguished from other parasitic organisms. 30. For a long time, Ozonium omnivorum was considered to be a sterile organism. Thornber and Duggar have found a spore stage in Arizona and Texas and they believed it to be the conidial stage of O. omnioorum, As a result of this finding, Duggar renamed the causal organism Phymatotrichum omnivorum. For the first time we TEXAS RooT R01‘. 5 have found this conidial spore stage in a pure culture grown on ster- ilized soil. These spores Whether collected in the field or from pure culture fail to germinate. It is, therefore, difiicult as yet to ascribe their true function. 31. By nature of its parasitic habit, all evidences tend to show that Phymatotrichum omnivorum is unable to maintain itself on dead or- ganic matter or in the soil, but that it needs and requires a living host on which to winter over. 32. Cotton roots, as Well as the roots of the perennial morning glory (Ipomoea trichocarpa) and perhaps others, act as living hosts on which the root rot fungus winters over. 33. Infection is active both during the summer and winter months, as long as there is a susceptible host in the field. 34. During the summer months infection is_ rapid and results in the killing of the affected host. The causal organism to maintain itself must migrate to an adjoining healthy host. During the winter months infection is slow, and but partially kills the affected host. 35. The causal organism in nature dies out with the death of its host, which is complete about fifteen to twenty days after it is uprooted. 36. Fall plowing when the soil is moist does not result in killing cotton roots or the roots of other perennials. 37. After the last cotton picking, the cotton roots should be pulled out and exposed to drying and to theleffect of weather for three or four weeks and then worked under. 38. Control methods can be successful only if based on a thorough knowledge of the life history of the causal organism. 39. Control methods should consist in entirely eliminating from the soil living susceptible roots of all kinds during the fall and winter months. This may be accomplished by frequent cultivation, by plow- ing when the soil is dry, and by using a system of fallow and rotation With non-susceptible hosts in which all weed carriers are eliminated. INTRODUCTION. Of the many. plant diseases in the State none perhaps surpasses in economic importance the Texas root rot. This disease affects not only the cotton but a large number of other crops. Early studies by the Texas Agricultural Experiment Station and by others have paved the way for the present work. This Bulletin presents as briefly as is consistent, results of studies of field and laboratory experiments car- ried on by the writers during the last six years. We believe that the information here presented points the way to new and fundamental methods of control as far as the cotton and other herbaceous crops are concerned. Future research will no doubt develop control methods applying to fruit trees, shrubbery, and other perennials. All the field experiments were carried on by both writers, who share equal respon- sibility for results presented. The laboratory work as well as the preparation of the manuscript was done by the senior writer, who accepts full responsibility for it. In this connection, we wish here to express our grateful acknowledg- 6 A A BULLF/ITIN N0. 307. ment to Mr. Sam Cater, a farmer of Bell County, for his cooperation in furnishing land to carry out new work or in duplicating field experiments which were tried at Substation No. 5 at Temple, the headquarters for all the field tests. The writers further wish to ex- press their indebtedness to Professor J. G. Brown of the Arizona Agricultural Experiment Station for sending spore material of Phyma- totrichum omnivorum for germination studies. . HISTORICAL. Texas root rot as a plant disease of economic importance was first recognized by the Texas Agricultural Experiment Station as early as 1888 through work done by Pammel (14 and 15) and by Curtis (3), previously of this Station. From 1888 to 1906 no considerable atten- tion was given this important disease. In 1907, Shear (20) and Miles (21 and 22) of the United States Department of Agriculture devoted some study to the control of cotton root rot by deep plowing. In 1916, Duggar (5) renamed the causal organism Phymatotrichum omwivorum (Shear) Duggar, because of the sport form which he found under field conditions. Recently (1919) Scofield (19) of the United States Department of Agriculture reported on studies of dead spots in cotton, which Will be referred to later. PRESENT WORK. In undertaking the present project, the writers deemed it necessary to check up the preliminary work carried out by others, because of the importance of such work, which paved the way to many phases still requiring a solution. The present investigation endeavored to estab- lish definitely the cause of the disease, the life history of the causal organism, the conditions which favor infection, the methods of spread, and the development, if possible, of practical methods of control. Many of these phases are practically completed, while others still re- quire further time and patient research. In a certain sense, the pres- ent Bulletin is really a report of progress. NAME OF THE DISEASE. The disease is variously referred to in literature as cotton blight, cotton wilt, root rot, Texas root rot, and alkali disease. Inasmuch as the Texas Agricultural Experiment Station was the first to recog- nize and to study this disease, and to distinguish this from other root troubles, the name Texas root rot is here adopted. This specifically refers to the root rot disease of cotton and all other susceptible crops, which is induced by the fungus Phymatotrichum omnivorum (Shear) Duggar. ECONOMIC IMPORTANCE. Pammel (14) in 1887 estimated that Texas lost $1,000,000 from the cotton root rot disease alone. This estimate, however, only repre- sented a fraction, since it was computed and based on information fur- nished by some fifty-seven cotton growers in the State. Orton (13) TEXAS R001" Ror. 7 figured that in» 1903, Texas 10st $2,000,000 from cotton root rot, while Shear and Miles (21 and 22) and Gilbert (8) estimated that in 1906, Texas lost nearly 1.3 per cent. of the cotton crop, amounting to about 52,600 bales, or a money loss of $3,000,000. These estimates, the present writers believe to be too low. For estimating losses from root rot, it is imperative to keep in mind the kind of season in which the disease has Worked. The trouble is undoubtedly far less serious during dry years than it is during wet seasons. In 1918, Which was a very dry year in Texas, the production of cotton in this State, as reported by the Monthly Crop Reporter of the United ‘States Department of Agri- culture, was stated as 2,580,000 bales. Furthermore, in the same year, the losses from Texas root rot of cotton were negligible _and conserva- tively estimated at about 5 per cent. of the total crop and equivalent to 130,000 bales. The year 1919, on the other hand, was wet, and Texas at that time produced 2,700,000 bales. The losses from root rot that year were conservatively placed at 10 ‘per cent., or a total of 313,900 bales. Likewise, in 1920, which was also a wet year, the Monthly Crop Reporter advises that Texas produced 11,200,000 bales. The losses from root rot that year were conservatively estimated* at about 15 per cent. or equivalent to a net loss of 630,000 bales. The sources of loss from the Texas root rot of cotton are threefold, (a) that which represents a dead net loss from plants which die early in the season before making any cotton whatsoever; (b) when the disease kills the plants just as the bolls are partly developed, resulting in few bolls and in an inferior grade of lint; (c) when the plants die comparatively late in the season after the bolls are matured, in which case the lint is not of the same high quality as that from bolls the plant of which remained alive during the entire season. The Writers believe that a conservative estimate of the annual loss from Texas root rot of cotton and all other economic crops will vary from fifteen to thirty million dollars. » Effect of Texas Root Rot on Price of Staple.—In order to more care- fully determine how closely estimates of losses from cotton root rot can be made, the following tests were carried out: During the fall of 1921, cotton bolls were picked at random in an infected field from fifty plants which had died comparatively late from the Texas root rot disease, and in which the lint seemed fully matured. The cotton from these bolls was picked out, thoroughly mixed, and placed in at paper bag labeled No. 1. Similarly, and in the same field, cotton bolls were collected from fifty other plants which died from root rot com- paratively early, that is, plants in which the bolls were undersized and few in number, and the lint was visibly of a low grade. The cotton from these bolls was picked out, well mixed, and placed in a paper bag marked No. 2. Finally, cotton bolls were gathered from fifty healthy plants; these bolls were of normal size, and the lint in them was fully formed and matured. The lint from these bolls was all picked out, carefully mixed up, and placed in a paper bag labeled No. 3. These *Estimates made by the senior author cooperating with the Plant Disease Sur- vey of the U. S. Department of Agriculture. 8 BULLETIN No. 307. three samples with their origin concealed were submitted t0 Mr. J. B. Beers, cotton classer of the Extension Division of the A. and M. Col- lege and of the United States Department of Agriculture. Mr. Beers was requested to estimate the approximate market money value of the three samples. The following were the results and are self-explan- atory: Sample No. 1, commanding a premium of only $7 to $10 per bale, staple reduced to 1 inch full, fair strength, but not as good as No. 3, though better than No. 2. Sample No. 2, commanding no premium, staple reduced to -§— inch, uneven, irregular and “wasty.” Sample N0. 3, commanding a premium of $17.50 to $20per bale, staple 1 1-16 inches full,~strong and even in character. The above ratings in no uncertain way indicate that the Texas root rot disease not only reduces the yield by killing younger plants and preventing their bearing, but also lowers the quality and hence the price of the staple. Efiect of Texas Root Rot on Strength 0f Cotton Ftber.—In order to further determine the efiect of the disease on the strength of the fiber, various samples of lint from healthy and diseased plants were submitted to the Oflice of Markets and Rural Organization of the ‘United States Department of Agriculture for testing. Mr. Fred Tay- lor, cotton technologist, reports on the results of his tests, which are given in Table 1. From this table, the following conclusions may be drawn: (a) The lint taken from plants killed by the Texas root rot disease and in which the bolls were fully developed but not matured was 30 to 40 per cent. weaker than the lint from healthy plants. (b) The lint taken from plants killed by the Texas root rot disease at a stage where the bolls were fully formed and properly ripened was p not apparently affected in strength of fiber. Table 1. Comparative individual fiber tests on samples of cotton taken from plants that had been killed by the root rot disease, and samples from healthy plants. Healthy Diseased Diseased Healthy Diseased Healthy l Diseased Totals...‘ 102.5 106.5 61.5 110.5 113.5 141.5 108.0 Averages..i 5.1 5.3 3.1 5.5 5.7 7.0 5.4 2.5 3.0 3.0 10.0 5.0 7.0 11.0 8.0 5.0 2.0 3.0 9.5 5.0 2.0 6.5 3.0 6.0 2.0 4.5 9.0 3.0 5.5 4.5 2.0 9.0 3.0 6.5 3.0 4.0 8.5 3.5 5.0 5.5 6.5 11.5 5.5 4.5 3.0 5.5 2.5 10.0 6.5 3.5 10.0 3.5 5.5 7.5 9.5 4.5 5.5 7.5 4.5 5.0 3.5 10.5 5.0 10.0 5.0 1.5 1.5 2.5 4.5 5.0 3.5 7.5 3.0 11.0 5.5 4.0 10.0 8.0 9.0 3.0 2.0 3.0 9.5 6.0 8.5 6.0 3.5 10.5 5.0 6.0 3.0 5.5 3.5 4.0 8.0 12.0 10.0 6.5 4.5 1.0 4.5 4.5 3.5 6.0 6.0 2.5 3.5 4.5 5.5 9.5 4.0 2.5 6.5 7.0 1.5 7.5 7.0 6.5 2.5 5.5 5.0 3.5 8.0 5.5 5.5 4.0 2.0 7.5 2.0 4.5 7.0 9.5 3.5 3.0 3.5 1.5 9.0 6.5 4.5 3.5 2.0 2.0 1.5 3.5 6.0 7.5 9.0 TEXAS Roor» ROT. 9 Efiect of Texas Root Rot on Seed Germinationh-The ill effect of the Texas root rot disease on the germination of the cotton seed will depend on the stage in which the plants die. Under actual field tests, we have repeatedly found that germination is not seriously affected when such seed came from plants which were killed by the disease at a late stage of maturity. Germination is, however, very poor in seed the mother plants of which were early affected by Texas root rot. The same observations are also supported by Pammel (14) and in Table 2, the germination tests of which were made by the Texas Branch Seed Laboratory. PROBABLE ORIGIN OF THSE TEXAS ROOT, BOT DISEASE. It is diflicult if not impossible to tell whether Texas root rot is indigenous to this State or whether it has been imported from else- where. Judging from its wide distribution in Texas and by the fur- ther fact that it is found killing native susceptible weeds on virgin land and even among timber, one is inclined to believe that the causal organism of Texas root rot is probably indigenous to this State, and it attracted attention with the extensive culture of the cotton crop. From Texas, the disease might have gradually spread to Arkansas, Arizona, New Mexico, and Southern California. It is probable that in time it may further extend into Louisiana, Mississippi, Alabama, and to the many other Southern States where soil and climatic con- ditions differ but little from those of Texas. Table 2. Effect of Texas root rot on seed germination. Du ration of i i Sample Source of cotton seed i tests in Germination No. i days l per cent. 1 l l . 4247 Plants killed by root rot at a late stage of maturity. . . . 10 85 4248 Plants killed by root rot early, bolls underdeveloped. . 10 34 4249 yPlants healthy, fully matured . . . . . . . . . . . . . . . . . . . . . . 1O 86 Recently (June 13, 1922) the senior writer received from W. Ohlen- dorf of the United States Federal Horticultural Board freshly-killed A cotton plants from Tlahualilo, Durango, Mexico. A careful study of these plants revealed unmistakable evidences of the Texas root rot disease, with the typical Phymatotrichu/m omnivorum fungus on the surface of the dead cotton roots. Further information from Mexico tends to indicate that the Texas root rot disease is even more severe there than it is in Texas. The reason seems obvious since most of the susceptible economic crops there are grown under irrigation. Exten- sive survey studies "in Mexico may throw new light on the probable origin of the disease. Until this is done, all else is speculation. DISTRIBUTION OF TEXAS ROOT ROT IN TEXAS. In referring to Fig. 1, one will see that Texas root rot has now been reported from sixty-seven counties in the State. This does not mean that the disease may not be present in other counties where it TO BULLETIN 30”’. ;;;; -n nan-1 CIVIL‘ nnnn 1; ¢¢¢¢¢¢¢¢ nu - » ~ n .4 AVAI4OIA “III! '\ 0:: / FIGURE 1. Present known distribution of Texas root rot of Texas. ’l‘nxAs Roor Ror. 11 attacks the native flora or even cultivated crops. The report of its occurrence in the sixty-seven counties is based on actual examinations of infected specimens sent in by growers or from field inspections by the writers. It is to be noticed from Fig. 1 that the Texas root rot disease is reported from two counties in East Texas, where the disease is not supposed to prevail because of different soil conditions there. Just how prevalent the disease is in East Texas is as yet little known. It is probable that soil conditions there are unfavorable for Texas root rot and that the cases reported are probably isolated spots with either surface or sub-surface soil favorable to the disease. This will be more definitely determined in the future. DISTRIBUTION OF TEXAS ROOT BOT IN THE UNITED STATES. According to Shear (20), Shear and Miles (21), Heald (10), Gil- bert (8), and others, the Texas root rot disease is known to occur in Texas, Southern Oklahoma, New Mexico», Arizona, and Southern California. Duggar (5) found it in» Oklahoma in 1915. Chambers (2), in 1919, refers to a root rot of trees in Oklahoma, evidently Texas root rot. We have been unable to obtain information on the exact distribution of the disease in Oklahoma. Under date of No- vember 30, 1921, Dr. Shear writes that he found the Texas root rot disease in New Mexico in the Pecos Valley. Professor Leonian, formerly of the New Mexico Agricultural Experiment Station, under date of November 22, 1921, writes as follows: “I have investigated rather carefully the root root of apple in New Mexico. It was re- ported to have been caused by Ozonium. I had dozens of sick and dead trees dug out, and found that in each case the tree was attacked by giant apple tree borers and wooly apple aphis.” Professor Leonian‘ further found that Talsa leucostoma Pers. was also killing apple trees in New Mexico. It seems, therefore, evident that as far as New Mexico is concerned, definite information is still lacking on the exact distribution and the economic importance of the Texas root rot dis- ease in that State. . In Arkansas, Elliott (6) reports traces of the disease in Miller County on the Red River. It seems that much of the Texas root rot in that State is mistaken for lightning injury. According to D. C. Georget (Plant Pathologist for the Arizona Commissior. of Agriculture and Horticulture), Texas root rot in Ari- zona is veiy widespread. The most serious infestation there is found in the irrigated districts of the river valleys, the disease apparently following the Gila River across the State. In Greenlee County, alfalfa, fruit, and ‘shade trees suffer heavily. In Graham County, alfalfa, cot- ton, fruit, and vegetables are equally attacked. The same is true for Pinal Cr qty near Florence and Sacaton. Perhaps the greatest losses from th. disease are found in Maricopa County, and in certain sec *Leonian, L. H. Studies on the Valsa apple canker in New Mexico. Phytopafl! 11:236-242, 1912. » tFrom correspondence dated December 22, 1921. ‘ ' 12 BULLETIN No. 307. FIGURE 2. a. Cotton plant freshly infected by root rot, showing drooping of foliame» b. Same as a, but five days later, foliage all shed, plant dead. c. and d. Splittin )f epidermis and softening of cambium layers of roots of cotton plants recently kill. Jy root rot. e. Two roots of infected cotton plants showing decay and breaking ofi? of the lateral roots. f. Root of cotton plant killed by root rot early in the fall and remaining un- disturbed in the field. Notice complete disappearance of epidermis and cambium lay- ers. g. Cotton root rot spot in which most of the plants were killed early, ‘result- ing in practically no cotton. , . TEXAS "Roor Ror. 13 tions of the Salt River Valley, especially near the towns of Mesa, Temple, Phoenix, and surrounding territories. The disease is further prevalent in the Buckeye Valley below the juncture of the Gila and Salt Rivers, and in the Gila Bend districts of cotton and alfalfa. The same is true for Yuma County, especially near the town of Somerton. The disease is likewise serious in Yavapai County from the town of Cottonwood to Camp Verde. In Pima County, the disease is espe- cially virulent in the Santa Cruz Valley, and in the Sahaurita district. In California, cotton culture is of but recent introduction. Accord- ing to Waite* the first cotton grown was in Calexico in 1902. From a mere beginning it increased to 1200 acres in 1909 and to 110,000 acres in 1917. In 1921, it was probably ten times as large. We have already stated that Dr. Shear and others have reported -the Texas root rot disease of cotton in Lower California. Mr. M. A. Ricej,‘ County Agent for 'Kern County, California, is authority for stating that there is some Texas root rot in the Imperial Valley, and that the disease is especially severe in the Palo Verde Valley, and in the San Pasqual Valley. _ Whether the Texas root rot is present in other Southern Cotton States is not known. When one considers the numerous agencies by which plant diseases may be transported it is indeed surprising that it has not as yet apparently gained a foothold in neighboring States like Louisiana, Mississippi, and Alabama. Whether the disease will in time spread to the other cotton States of the South or whether it will remain restricted to its present area is difficult to predict. SYMPTOMS OF THE TEXAS ROOT ROT DISEASE. The symptoms of Texas root rot differ but little as it affects the various susceptible hosts, and, for this reason, the disease is frequently mistaken for other troubles. Susceptible herbaceous hosts seldom show any evidence of being stunted or of turning yellow, as is the case with many other diseases. On the contrary, the plants look normal and healthy, and wilting is sudden in which the entire foliage droops (Fig. 2, a) and dies, and after one to two days the leaves become- blackened, shrunken, and in most cases drop off, leaving a bare dead stalk (Fig. 2, b). An infected cotton plant, for instance, seldom revives, although it may do so during prolonged wet weather when the affected host endeavors to send out new rootlets above the diseased area. Such a plant seldom survives for very long, but dies with the advent of dry weather. When a freshly-infected plant that has been dead two or three days is pulled out, the outer surface of its root will generally be found cracked (Fig. 2, c and d), the cambium softened, and the epidermis covered with numerous yellowish threads of the causal organism. Both epidermis and cambium readily peel off with‘ the least scratch of the finger, exposing the unsoftened woody portion of the tap root. If a dead plant remains in the ground for eight *Waite, F. A., Cal. Month. Bul. of the State Comm. of Hort, 6:427-429, 1917. iCorrespondence dated December 3, 1921. 14 BULLETIN -No. 307 . days or more, both the epidermis and cambium rot and disappear, leav- ing a short woody stub of the affected root (Fig. 2, e and f), which becomes afertile field for a rich mycological flora. With all susceptible hosts, the disease in every case is confined to the roots, although it occasionally works up an inch or two to the foot end of the plant above ground. The diseased area at the foot. of the plant is distinguished from the healthy tissue above by a marked constriction, which is sharply defined in the freshly wilted host (Fig. 3, i and h). During wet weather, in addition to the presence of the characteristic mycelial threads on the surface of the affected root, numerous wart-like bodies (Fig. 3, g, h, and i‘) may also be present. These are frequently common on cotton and on okra. Heald and Wolf (12) met with this condition in a field of infected cotton at Fal- furrias, Texas, and they believed it to be a new disease. According to their own description, “the dead plants exhibiting much the same general appearance as in the case of the well-known Texas root rot * * *” “Numerous small xvart-like pustules also appear on the main root * * *” (Fig. 3, i). ' Our own studies have shown that both cotton and okra frequently produce numerous corky lenticles at the root and foot end of the plant. These lenticles become very prominent and with age resemble wart- like excrescences (Fig. 3, g). If these plants succumb to Texas root rot, the Phymatotrichum strands will be found to collect and to over- run the exterior and partly even the interior of the tissue, giving the appearance of a pseudo-sclerotium. In some instances, the causal or- ganism would even form pseudo-sclerotia-like bodies on infected cotton or okra roots without the presence of corky lenticles. Furthermore, and as we shall show later, p. 6'7, Phymatotr/ichum omnivorum fre- quently produces pseudo-sclerotia on culture media. This indicates that Heald and Wolf (12) did not deal with any new cotton disease, and that the warts on affected plants are frequently part of an. addi- tional symptom of Texas root rot. With trees, as with the apple, for instance, the symptoms are the same as with herbaceous plants. This is evidenced by sudden wilting and dying of the foliage 3, a). Later the dead leaves drop off exposing the dead bare limbs (Fig. 3, b). In pulling out a freshly-wilted cotton plant and in removing the outer epidermis and cambium, one finds that the woody portions of the root lying immediately underneath are deeply discolored, brown to chocolate (Fig. 3, f). Furthermore, the healthy tissue is sharply marked off from the diseased area (Fig. 3, f) by a dark line. This area is invariably free from fungus hyphae, and it tends to show that the causal organism kills its host tissue in advance of its penetration and invasion. The toxic substance secreted by the causal organism is probably of enzymic origin. TIME OF FIRST APPEARANCE AND LATER SPREAD OF ROOT ROT DURING THE SUMMER. Opinions differ about the time in which the root rot disease of cotton first appears in an infected field. Pammel (15) records instances TEXAS RooT R01‘. 15 FIGURE 3. a. Apple tree recently killed by root rot, showing wilted, clinging foliage. b. Same as a, but one month later showing bare limbs, tree dead. c. Living cotton roots wintered over in the field, showing the blackened stem which was killed by fall frost and the white living roots which stayed in the soil. d and e. Like c, but showing method of root rot infection during the winter months, in which the disease is con- fined to the tip of the root and without completely killing it. f. Root of cotton killed by root rot during the summer, resulting in immediate and complete dying of the affected root. i. Cotton root killed by root rot, showing constriction and sclerotia- like bodies (i after Heald and. Wolf). h. Same as w; (original). g. Same root as h magnified to show enlarged lenticels which frequently become invaded by phymato- trichum hypheae, and resemble sclerotial bodies. I6 BULLETIN No. 307. brought to his attention in which young cotton was claimed to be killed by the disease as early as May. From our own work we have found this to be the case. However, the Texas root rot- is never serious on young cotton and the probable reason will be referred to on page 1'7. The early summer spread will depend on the number of perennial_ susceptible weeds or infected cotton roots which were permitted to live over during the previous winter months. During July or August, depending on rainfall conditions, the Texas root rot disease in cotton always starts with one or two dead plants in the field. As the season advances, weather conditions being favor- able, the disease slowly but gradually spreads, involving in many cases large numbers of dead plants and assuming the shape of spots (Fig. 2, g), which are more or less circular in outline. Definite studies are still lacking as to how rapidly or slowly the disease spreads in the same spots under varying weather conditions during the summer season. The spread of Texas root rot during the fall and winter months is discussed under “life history studies,” page '72. SPREAD OF ROOT ROT FROM FIELD TO FIELD. No satisfactory explanation can as yet be given of the sudden appear- ance of the root rot disease in new fields. Reference has already been made to the fact that native susceptible weeds are found to die from Texas root rot in virgin and in timber lands. Nevertheless, there seems to be another factor of spread to be reckoned with. This factor is probably the fruiting stage of the causal organism which Duggar (5) has described and named Phymatotrichum omnivorum. This will be further considered under life history, page '72. Heald (9) claims that root rot is spread from one field to another through fragments of fungus threads which are carried with soil par- ticles by wind, or through the tools which are used during tillage, or through birds and working animals. The writers seriously question whether root rot ever spreads in that fashion. If this were true, the- spots would naturally follow the direction of the plow and the cul- tivator. Furthermore, numerous secondary spots would appear in the same field in the summer as a result of infected particles of soil car- ried by implements, or wind. Field observations during the last six years tend to show that a given number of centers of infection appear in the same field early in the season and that these centers first orig- inated where living susceptible roots carried the causal organism over winter. These then spread and increase in» size rather than in num- ber irrespective of direction in cultivation. Furthermore, numerous attempts of transferring soil from a freshly-infected plant to a healthy distant plant never reproduced the disease. SPREAD OF ROOT ROT IN THE SAME FIELD. We have observed time and again that the root rot spreads through direct contact in the soil of an infected cotton root of one plant with that of an adjoining healthy root of another. Texas root rot may also spread from an infected to a healthy cotton root through intermediary TEXAS RooT RoT. l7 susceptible weed hosts, of which there are many. For this reason, it is conceivable why early-planted cotton is always more susceptible and the root rot spots are larger during favorable seasons than is actually the case in very late-planted cotton. The explanation appar- ently lies in the difference in root system. Late-planted cotton ordi- narily escapes many of the beneficial rains, and as a result forms a smaller tap root and few and shorter laterals, which are not apt to meet so readily with the roots of neighboring plants. With early- planted cotton, on the other hand, the root system is well developed, producing not only a longer tap root, but also numerous well-developed laterals, which travel in every direction and which invariably meet and overlap the lateral roots of neighboring cotton plants. These ob- servations, which were frequently verified by us through actual field studies of the root system, seem to strengthen our claim that Texas root rot spreads by means of underground contact of the roots. This is also substantiated by Toumey (80), who has observed that with alfalfa the disease spreads by contact of the infected roots of one plant with those of a neighboring healthy plant. The same is espe- cially true with the okra, the castor bean, and many other susceptible hosts which possess a well-developed system of lateral roots. This is especially apparent in such susceptible crops which naturally require close sowing or planting such as beets, carrots, or alfalfa and sweet clover. In such cases, the root rot spots seem to enlarge much faster in a given time than seems the case with the cotton, which has a more restricted root system and which requires more space between the rows. Further evidence of the method of underground spread of Texas root rot by means of root contact is hardly warranted. If this were not the case, we should find hundreds of plants dying all at once in a given spot. This, however, is the exception. During active spread of the disease, it isseen that freshly-infected plants are invariably found to follow those which border on those which have died a day or two before. In a so-called root rot spot, the freshly-infected plants are always found on the outer edge and within the immediate neighborhood of a dead plant or plants within. SHAPE OF ROOT ROT SPOTS. It is generally believed that Texas root rot spots are always circular and for this reason the disease is mistaken for alkali spots. It is not uncommon to find the spots to take on every conceivable‘ shape or form. A case under observation is that of a cotton field in Bell County in which the root rot spot took on the shape of a large crescent with apparently no other dead spots in the field. No attempt has been made to ascertain whether this condition was purely accidental. Root rot spots are more or less circular in vigorous cotton which possesses a well-developed system of laterals which penetrate deeply in the soil, thus escaping destruction by cultivators. This condition is especially true with the okra, the castor bean, and other such susceptible crops which are deep rooted. On the other hand, with shallow-rooted plants, chief of which may be mentioned. the cowpea, root rot spots lose all 18' BULLETIN N0. 307. their circular outline, and the disease is frequently confined to the length of each row. In this case, the seed are planted quite closely in the row, a circumstance that causes very close contact and inter- lapping of the root system. Here, then, the disease may frequently follow the entire length of the rows. Likewise, Texas root rot seldom appears in spots in closely-planted crops such as carrots and beets, where there is practically direct contact in the roots, but attacks an entire row or more. HOW THE TEXAS ROOT BOT DIFFERS FROM OTHER COTTON DISEASES. Cotton is subject to three other diseases for which Texas root rot may often be mistaken, namely: alkali injury, lightning injury, and Fusarium wilt. Alkali Injury. The reason Texas root rot is frequently mistaken _ for alkali injury is that the latter trouble always appears in spots. Dr. G. S. Fraps, Chief Chemist of the Texas Agricultural Experiment - Station, in a recent press bulletin, says thatalkali ‘spots are common in many parts of the State. These spots have no connection with the Texas root rot disease. A case of alkali spot was reported from Hill County. Four years ago the spot barely covered a few square feet, . and now it occupies four acres. Such spots contain an excess of vari- ous salts, including ordinary table salt. In alkali spots, cotton will barely sprout, corn will not grow, and even ordinary weeds will straggle along with great difficulty. On the other hand, in typical root rot spots, corn as well as every other grain or cereal crop will grow per- fectly. Furthermore, in these same spots, cotton plants will germinate and grow normally until bearing, when they will usually succumb in greatest number to the root rot disease. Likewise, in these spots the alkali present, if any, is in such small quantities as to be practically harmless. This is shown in Table 22. i Lightning Injury. So far, the writers have not seen or observed dead spots on cotton which were induced by lightning. Elliot (6), on the other hand, states that during seasons of frequent thunder storms, this source of injury is common in Arkansas. The injured spots are circular, with the first dead plants appearing in the center. Affected plants do not always die at once, but frequently linger in a wilted state for several weeks. Such spots according to Elliot (6) are frequently mistaken for Texas root rot spots. Plants which die early from lightning injury show no peculiar symptoms. However, those which succumb later exhibit an injured area at the surface of the soil, above which the stem of the plant has enlarged and below which, although the root may still be alive, there has been no growth; these are the marks that distinguish it from Texas root rot injury, the symptoms of which are given on page 13. Wilt. This disease is mostly confined to thesandy soils and sandy loams in Texas as contrasted to the Texas root rot disease, which is mostly found in the black, waxy, and compact soils. Wilt is caused by a fungus, Fnsarium vasinfectum. Atk., which lives in the soil and p TEXAS RooT RoT. 19 infects the plants through the young rootlets and penetrates the main root, stem, petioles, and even leaves. The causal organism invades the interior fibrovascular or water-carrying vessels of the plant, cutting" off the water supply from the soil and causing a sudden wilting of the foliage, a frequent reviving over night or during rainy Weather, and a gradual slow dying of the entire plant. The diseased leaves drop off at the least touch, leaving a bare stalk, which may remain green a a long time, and even send out new sprouts. Outwardly, there are no visible symptoms of this disease except the wilting, which is very pronounced in dry weather. However, when one splits open length- wise the roots and stem of an affected plant, the interior Woody por- tions of both roots and stems are found to be darkened, a condition- indicating the presence of the causal organism. This, then, distin- guishes the Fusarium wilt from Texas root rot; the latter attacks the- roots only, and never any parts of the plant above ground. Further- more, the Fusarium wilt fungus lives over Winter in the soil and on dead remnants of the cotton plants, which is not the case with the- causal organism of Texas root rot. ' HOSTS AFFECTED. In studying the life history of any plant parasite, one must deter-- mine its range of host. This is equally important from a practical‘ point of view when we consider methods of control. In order to definitely determine the range of hosts which were sus- ceptible or resistant to Texas root rot, our attention was given to grow-- ing and testing out as many of the economic crops as we could obtain through limited funds. Many of the ornamentals were secured through the cooperation of the United States Department of Agriculture. The tests on forest and shade trees were carried out in cooperation with the State Forester, Mr. E. O. Siecke, who was kind enough to furnish the material. Most of the tests reported in Table 3 are based’ on five years’ studies and observations beginning with 1917 and continuing" and including the season of 1922. The degree of susceptibility or re- sistance as indicated in Table 3 is expressed in letters. A denotes complete resistance; B, fifteen per cent. susceptible; C, fifteen to thirty per cent. susceptible; D, thirty to sixty per cent. susceptible; E, sixty to ninety per cent. susceptible; F, ninety to one hundred per cent. susceptible. It should be added that this scale is only’ relative and is intended merely as a guide. These trials, before furnishing an abso- lute guide, should be carried on during a period of several more years, and cover larger percentages. It is, of course, probable, that after several more years of study and observations, some of thehosts indi- cated as resistant may prove to be slightly susceptible _or very sus- ceptible. In this case, our present conception, of their susceptibility or apparent resistance may have to be modified when these hosts are tested for a longer period of time. This is especially true with trees and shrubs. In this connection it will not be out of place to cite an illustration with the peach. For twelve years a number of peach trees grew in an orchard at Substation No. 5 at Temple, Texas. In 2O BULLETIN N0. 307. this same orchard, we grew for the last seven years cotton, which every year died from Texas root rot, whereas the peach trees there remained healthy. Early in the summer of 1922, four peach trees suddenly turned pale, the fruit failing t0 develop, the foliage shedding pre- maturely, and by the end of the season the trees were dead. Two were dug out, and a close examination with the naked eye and under the microscope revealed the presence of Phymatotrichum omnivorum, and another coarse yellow sterile fungus on the dead roots. The ques- tion arises as to which of these fungi killed the peach trees. From this it is evident that it is necessary to grow trees and shrubs for a large number of years in sick land before we can definitely classify them as to resistance to Texas root rot. Table 3. Relative resistance or susceptibility of various hosts to Texas root rot. I 1 V _ . _ Relative Common name Scientific name resistance or susceptibility Family Aceraceae. Box Elder . . . . . . . . . . . . . . . . . . . . . . . Acer negundo . . . . . . . . . . . . . . . . . . . . . . . C Maple (sugar) . . . . . . . . . . . . . . . . . . . . Acer saccharinum. . . . . , . . . . . . . . . . . D Maple (Chinese) . . . . . . . . . . . . . . . . . Acer saccharznum chznenszs. . . . . . . . . . . C Family Amarantaceae. _ Amaranth . . . . . . . . . . . . . . . . . . . . . . . Amaranthus tricolor . . . . . . . . . . . . . . . . . A Alternanthera . . . . . . . . . . . . . . . . . . . . Alternanthera spp . . . . . . . . . . . . . . . . . . . A Coxcomb . . . . . . . . . . . . . . . . . . . . . . . . Celosza crlslata . . . . . . . . . . . . . . . . . . . . . A Pigweed, tall . . . . . . . . . . . . . . . . . . . . . Amaranthus retroflexus . . . . . . . . . . . . . . A Pigweed, Red Root . . . . . . . . . . . . . . . Amaranthus hylmdus . . . . . . . . . . . . . . . . A Spiny Amaranth . . . . . . . . . . . . . . . . . Amaranihus spmosus . . . . . . . .i . . . . . . . . A Family Amaryllidaceae. _ _ Daffodil . . . . . . . . . . . . . . . . . . . . . . . . . N(U'_Cl88llS bulbocodzum . . . . . . . . . . . . . . . A Tuberose . . . . . . . . . . . . . . . . . . . . . . . . Polzanthestuberosa . . . . . . . . . . . . . . . . . . A Family Ambrosiaceae. _ . Cocklebur . . . . . . ._ . . . . . . . . . . . . . . Xanthium commune . . . . . . . . . . . . . . . . . D Cocklebur . . . . . . . . . . . . . . . . . . . . . . . Xanthliim strumarzum._ . . . . . . . . . . . . . . C Ragweed . . . . . . . . . . . . . . . . . . . . . . . . Ambrosia artemlszaefolza . . . . . . . . . . . . . C Family Ampelideae. _ _ _ _ Grape . . . . . . . . . . . . . . . . . . . . . . . . . . . Vztzs vznzfera . . . . . . . . . . . . . . . . . . . . . . . C -Family Anacardiaceae. _ _ _ _ Pistache, Chinese . . . . . . . . . . . . . . . . . Plstache chznenszs . . . . . . . . . . . . . . . . . . . D Family Apocynaceae. _ _ leander . . . . . . . . . . . . . . . . . . . . . . . . Nerzum Iaurzforme . . . . . . . . . . . . . . . . . . A Periwinkle . . . . . . . . . . . . . . . . . . . . . . . Vznca minor . . . . . . . . . . . . . . . . . . . . . . . A Family Araceae. _ Dasheen . . . . . . . . . . . . . . . . . . . . . . . . . Colocasza spp . . . . . . . . . . . . . . . . . . . . . . . A Family Araliaceae, _ _ _ Sarsaparilla vine . . . . . . . . . . . . . . . . . Aralza nudzcaulzs . . . . . . . . . . . . . . . . . . . B Family Asclepiadaceae. _ Milkweed . . . . . . . . . . . . . . . . . . . . . . . Ascleplas speczosa . . . . . . . . . . .v . . . . . . . . A Family Begoniaceae. _ atalpa . . . . . . . . . . . . . . . . . . . . . . . . . Calalpa speczosa . . . . . . . . . . . . . . . . . . . . C Family Cactaceae. _ _ _ V Cactus, all varieties . . . . . . . . . . . . . . Opuntza spp . . . . . . . . . . . . . . . . . . . . . . . . A Family Cannaceae. I _ Canna, edible . . . . . . . . . . . . . . . . . . . . Canna edulzs . . . . . . . . . . . . . . . . . . . . . . . A Canna, ornamental . . . . . . . . . . . . . . . Canna spp . . . . . . . . . . . . . . . . . . . . . . . . . A Family Caprifoliaceae. _ E der Berry . . . . . . . . . . . . . . . . . . . . . Sarribucus canadenszs . . . . . . . . . . . . . . . B Honeysuck e . . . . . . . . . . . . . . . . . . . . . Lonzcera spp . . . . . . . . . . . . . . . . . . . . . . . A TEXAS Roots RoT. 21 Table 3. ‘Relative resistance or susceptibility of various'_hosts to'_Texas root rot —C ontinue . _ Relative Common name Scientific name resistance _or SUSCQ-ptlblllty Family Caryophyllaceae. _ Carnation . . . . . . . . . . . . . . . . . . . . . . . Dzantlius caryophyllus . . . . . . . . . . . . . . . A Chickweed . . . . . . . . . . . . . . . . . . . . . . . Cerastzum vulgatum . . . . . . . . . . . . . . . . . A Pink . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dlanthus spp . . . . . . . . . . . . . . . . . . . . . . . A Family Cheno odiaceae. Beets, al varieties . . . . . . . . . . . . . . . Beta vulyaris . . . . . . . . . . . . . . . . . . . . . . . C to D Lamb’s uarter . . . . . . . . . . . . . . . . . . Chenopodium album . . . . . . . . . . . . . . . . . C Russian histle . . . . . . . . . . . . . . . . . . Salsola pestiveri . . . . . . . . . . . . . . . . . . . . . Spinach . . . . . . . . . . . . . . . . . . . . . . . . . Spinacia oleracea . . . . . . . . . . . . . . . . . . . C to D Swiss Chard . . . . . . . . . . . . . . . . . . . . . Bela sp . . . . . . . . . . . . . . . . . . . . . . . . . . . . D Family Cichoriaceae. _ Prickly Lettuce . . . . . . . . . . . . . . . . . . Lactuca scarzola . . . . . . . . . . . . . . . . . . . . D Sow Thistle . . . . . . . . . . . . . . . . . . . . . Sonchus asper . . . . . . . . . . . . . . . . . . . . . . B Family Comlfiiositae. _ Articho , Jerusalem . . . . . . . . . . . . . . Helzanthus tuberosus. . . . . . . . . . . . . . . . . C Artichoke, Globe . . . . . . . . . . . . . . . . . Cynara scolymus . . . . . . . . . . . . . . . . . . . . C Cosmos . . . . . . . . . . . . . . . . . . . . . . . . . Cosmos spp . . . . . . . . . . . . . . . . . . . . . . . . . A a Daisy, Shasta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ._ . . . . . . . . . . . . . . . . . . . . . . . . A Lettuce, Big\Boston . . . . . . . . . . . . . . Lactuca satwa . . . . . . . . . . . . . . . . . . . . . . B Lettuce, Prize Head . . . . . . . . . . . . . . Lactuca sativa . . . . . . . . . . . . . . . . . . . . . . B Rosin\Weed . . . . . . . . . . . . . . . . . . . . . Grindelia squarrqsa ._ . . . . . . . . . . . . . . . . A Salsify . . . . . . . .v . . . . . . . . . . . . . . . . Tragopogon porrlfollus . . . . . . . . . . . . . . . D Sunflower, Russian . . . . . . . . . . . . . . . Helzanthus annuus, . . . . . . . . . . . . . . . . . D Sunflower, Wild . . . . . . . . . . . . . . . . . . Ilelianthus petiolarls . . . . . . . . . . . . . . . . C Thistle, Canada . . . . . . . . . . . . . . . . . . Carduus arvensis . . . . . . . . . . . . . . . . . . . . A Thistle, Common . . . . . . . . . . . . . . . . . Carduus lanceolatus . . . . . . . . . . . . . . . . . A Family Coniferae. , _ _ Arbor vitae . . . . . . . . . . . . . . . . . . . . . . Thuja orzentalzs. . . . . . . . . . . . . . . . . . . . A to B Cypress, Smooth . . . . . . . . . . . . . . . . . Capressus glabra . . . . . . . . . . . . . . . . . . . . C Pine . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pznus spp . . . . . . . . . . . . . . . . . . . . . . . . . . C Pine, Chinese . . . . . . . . . . . . . . . . . . . . Pinus chinensis . . . . . . . . . . . . . . . . . . . . . C Family Convulvulaceae. _ Cypress vine. . . ._ . . . . . . . . . . . . . . . . . I pomoea quamocllt . . . . . . . . . . . . . . . . . . A Ivy-leaved Morning Glory . . . . . . . . . I pomoea hederacea . . . . . . . . . . . . . . . . . . C Moonflower. . . . ._ . . . . . . . ._ . . . . . . . . . Ipomoea grandiflora alba . . . . . . . . . . . . . A Small-flowered pink Morning Glory. I pomoea trzchocarpa . . . . . . . . . . . . . . . . . B to C Sweet Potato . . . . . . . . . . . . . . . . . . . . I pomoea batatas . . . . . . . . . . . . . . . . . . . . E Family Cornaceae._ _ Dogwoo . . . . . . . . . . . . . . . . . . . . . . . . Cornus Florida . . . . . . . . . . . . . . . . . . . . . C Family Cruciferae. lyssum, Sweet . . . . . . . . ._ . . . . . . . . . Alyssum odoralum . . . . . . . . . . . . . . . . . . A Broccoli, Early Large White . . . . . . . Brassica sp . . . . . . . . . . . . . . . . . . . . . . . . . B Brussels Sprouts, Improved Long _ I Island . . . . . . . . . . . . . . . . . . . . . . Brassica sp . . . . . . . . . . . . . . . . . . . . . . . . . B Cabbage . . . . . . . . . . . . . . . . . . . . . . . . . Brassica oleracea . . . . . . . . . . ._ . . . . . . . . . B Cauliflower . . . . . . . . . . . . . . . . . . . . . . Brassica oleracea, var. Botrytzs . . . . . . . . B Collard, Georgia or Southern Creole Brassica sp . . . . . . . . . . . . . . . . . . . . . . . . . B Horseradish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D Kale . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brassica oleracea, var. Ace hala . . . . . . B Kohl Rabi . . . . . . . . . . . . . . . . . . . . . . . Brassica oleracea, var Cau o-Rapa . . . . B .Mustard, Southern Giant, Curled.. . Brassica J aponica . . . . . . . . . . . . .~ . . . . . B Mustard, Qhinese . . . . . . . . . . . . . . . . . Brassica J uncea_. . . . . . . . . . . . . . . . . . . . B Nasturtium, Tall . . . . . . . . . . . . . . . .. Tropaeolum majus . . . . . . . . . . . . . . . . .. A Nasturtium, Dwarf . . . . . . . . . . . . . . . Tropaeolum minus . . . . . . . . . . . . . . . . . . A Radish . . . . . . . . . . . . . . . . . . . . . . . . . . Raphnus sativus . . . . . . . . . . . . . . . . . . . . B Rape, Dwarf Essex . . . . . . . . . . . . . . Brassica napus . . . . . . . . . . . . . . . . . . . . . B c . . . . . . . . . . . . . . . . . . . . . . . . . . . M atthlola mcana . . . . . . . . . . . . . . . . . . . A Turnip, all varieties . . . . . . . . . . . . . . . Brassica rapa. . . . . . . . . . . . . . . . . . . . . . B Watercress . . . . . . . . . . . . . . . . . . . . . . Roripa nasturtium. . . . . . . . . . . . . . . . . . A Family Cucurbilaceae. ' ron. . . . . . . . . . . . . . . . . . . . . . . . .. Citrullus sp. . ._. . . . . . . . . . . . . . . . . . . .. A Cucumber, Small Gherkin . . . . . . . . . Cucumis anyuria . . . . . . . . . . . . . . . . . . . A Cucumber, Klondike . . . . . . . . . . . . . . Cucumis sativus . . . . . . . . . . . . . . . . . . . . A Cassaba, Honey Dew Melon . . . . . . . Cucumis melo . . . . . . . . . . . . . . . . . . . . . . A Muskmelon, Texas Cannonball. . . . . Cucumis melo . . . . . . . . . . . . . . . . . . . . . . A Muskmelon, Burrell’s Gem . . . . . . . . Cucumis melo . . . . . . . . . . . . . . . . . . . . . . A Muskmelon, Rockyford_ . . . . . . . . . . . Cucumzs melo . . . . . . . . . . . . . . . . . . . . . . A Pumpkin, Mammoth Kin . . . . . . . . . Cucurbita pepo . . . . . . . . . . . . . . . . . . . . . A Pumpkin, Green Striped ushaw. . . Cucurbita pepo . . . . . . . . . . . . . . . . . . . . . A 2 BULLETIN N0. 307. Table 3. Relative'resistance or susceptibility of VariousIhosts to Texas root rot —-—C ontinued. Relative resistance or susceptibility Common name Scientific name Family Cucurbitaceae—Continued. Pumpkin, Big Four . . . . . . . . . . . . . . . Cucurbita pepo. . . . . . . . . . . . . . . . . . . . . Squash, Giant Summer Crookneck. . Cucurbita pepo . . . . . . . . . . . . . . . . . . . . . Squash, Patty Pan . . . . . . . . . . . . . . . Cucurbita pepo. . . . . . . . . . . . . . . . . . . . . Watermelon, all varieties . . . . . . . . . . Citrullus vulgaris . . . . . . . . . . . . . . . . . . . Family Cupuliferae. estnut, American Sweet. . . . . . . . . Castanea saliva . . . . . . . . . . . . . . . . . . . . . Oak, Scrub . . . . . . . . . . . . . . . . . . . . . . Quercus, sp . . . . . . . . . . . . . . . . . . . . . . . . .» Oak, Bur . . . . . . . . . . . . . . . . . . . . . . . . Quercus m_acrocarpa . . . . . . . . . . . . . . . . . Oak, Water . . . . . . . . . . . . . . . . . . . . . . Quercus mgra. . . . . . . . . . . . . . . . . . . . . . Oak, Live. . . . . . . . . . . . . . . . . . . . . . . Quercus virginiana . . . . . . . . . . . . . . . . . . Oak, Post . . . . . . . . . . . . . . . . . . . . . . . Quercus minor . . . . . . . . . . . . . . . . . . . . . . Family Cyperaceae. Chufas or Earth Almond . . . . . . . . . . Cyperus esculentis . . . . . .' . . . . . . . . . . . . . Nut Grass . . . . . . . . . . . . . . . . . . . . . . . Cyperus spp . . . . . . . . . . . . . . . . . . . . . . . . Sedges . . . . . . . . . . . . . . . . . . . . . . . . . . Carex spp. . . . . . . . . . . . . . . . . . . . . . . . . P“ ‘In Family Dioscorea. _ Yam, Tropical . . . . . . . . . . . . . . . . . . . Dioscorea sp . . . . . . . . . . . . . . . . . . . . . . . . Yam, Tropical . . . . . . . . . . . . . . . . . . . Dzoscorea sp . . . . . . . . . . . . . . . . . . . . . . . Family Ebenaceae. _ _ 0 Persimmon, Native . . . . . . . . . . . . . . . Diospyros vzrginiana . . . . _ . _ . . . . . . . . . Persinlmen, Japanese . . . . . . . . .‘ . . . . Dzospyros Kakz . . . . . . . . . . . . . . . . . . . . . Family Euphorbiaceae. _ nrcaflller Bean - - - - - - - - - - - - - - - - - - - -- Rzcinus communis . . . . . . . . . . . . . . . . .. Castor Bean, Ornamental. . . . . . . . . Ricinus, spp . . . . . . . . . . . . . . . . . . . . . . . . Snow-omthe-mountaln . . . . . . . . . - - - Euphorbia marginata . . . . . . . . . . . . . . . . spurge, Flewerlng - - - - - - - - - - - - - - - - Euphorbia corollata . . . . . . . . . . . . . . . . . spurge, Spurred - - - - - - - - - - - - - - - - - - Euphorbia cyparissias . . . . . . . . . . . . . . . Tallow Tree. . . . . . ._ . . . . . . . . . . . . - - Sapium sebriferum. . . .. . . . . . . . . . . . . . . Weed, Oil Tree, Chlneee - - - - - - - - - - Aleurites fordii . . . . . . . . . . . . . . . . . . . . . Family Geraniceae. _ Geranium. . .. . . . . . . . . . . . - - - . - - - - - Geranium spp . . . . . . . . . . . . . . . . . . . . . . Geranium, Wlld - - - - - - - - , - - - - - - - - - Geranium carolianum . . . . . . . . . . . . . . . . Family Ginkgoaceae. Ginkgo Tree, J apanese - - . - . - - . - - . . Ginko bialoba . . . . . . . . . . . . . . . . . . . . . . Family Graminae. ar Y- -- - - - - - - - - - - - - - - - -- - - - - - - - - Hordeum sativum . . . . . . . . . . . . . . . . . . . Broom Sed e . . . . . . . . . . . - - - - - - - - - Andropogon virginicus . . . . . . . . . . . . . . . Cheat or C ess._ . . . . . . . . . . . - - - - - - - Bromus secalinus . . . . . . . . .* . . . . . . . . . . Corn, all varieties . . . . . . . . . . . . . . . . Zea Mays _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Cern, BrOOm - - - - - - - - - - - - - - - - - - - - - Andropogon sorghum var. technicus. . . . Durra . . . . . . . . . . . . . . . . . . . . . . . . . . . Andrgpgggn sopghum _ _ _ _ _ _ _ _ _ _ _ _ _ _ Emmer . . . . . . . . . . . . . . . . . . . . - - - - - - - Triticum sativum var. dicoccum . . . . . . . Grass, Barnyard - - - - - - - - - - - - - - - - - - Echinochloa crusgalli . . . . . . . . . . . . . . . . Grass, Bermuda - - - - - - - - - - - - - - - - - - Capriola dactylon . . . . . . . . . . . . . . . . . . . Grass, BIOOIII - - - - - - - - - - - - . . - . - - - - Bromus enermis . . . . . . . . . . . . . . . . . . . . Grass, Crab - - - - - - - - - - - - - - - - - - - - - - Digitaria sanguinalis . . . . . . . . . . . . . . . . Grass, Feseue - - - - - - - - - - - - - - - - - - - - F estuca elatior . . . . . . . . . . . . . . . . . . . . . . Grass, FeXtail - - - - - - - - - - - - - - - - - - - - Setaria viridis . . . . . . . . . . . . . . . . . . . . . . Grass, Jehnsen - - - - - - - - - - - - - - - - - - - Sorghum halepense . . . . . . . . . . . . . . . . Grass, Pigeen; - - . - - - - - - - - - - - - - - - - - Selaria glauca . . . . . . . . . . . . . . . . . . . . . . Grass, Mesgulte - - - - - - - - - - - - - - - - - - Hzlaria penchroidea . . . . . . . . . . . . . . . . . Grass, B110 e8 - - - - - - - - - - - - - - - - - - - Chloris gayana . . . . . . . . . . . . . . . . . . . . . ‘ Grass. Sudan , - - - - - - - - - - - - - - - - - - - Andropogon sorghum var. sudanensis. . Grass, Wlre" ' ' ' ' ' ' ' ‘ ' - - - - - - - - - - - - Paspalum distichum . . . . . . . . . . . . . . . . . Grass, Wlieh - - - - - - - - - - - - - - - - - - - - - Panicum capillare . . . . . . . . . . . . . . . . . . Kaoliang . . . . . . . . . . . . . . . . . . . . . . . . Andropogon sorghum . . . . . . . . . . . . . . . . Kafir . . . . . . . . . . . . . . . . . . . . . . . . . . . Andropogon sorghum . . . . . . . . . . . . . . . . Millet . . . . . . . . . . . . . . . . . . . . . - . . - . - Chaetochloa italica. . . . . . . . . . . . . . . . . . Milo . . . . . . . . . . . . . . . . . . . . . . . . . . . . Andropogon sorghum . . . . . . . . . . . . . . . . Oats, cultivated . . . . . . . . . . . . . . . . . . Avena saliva . . . . . . . . . . . . . . . . . . . . . . . Rye. . .» . . . . . . . . . . . . . . . . . . . . . . . . . Secale cereale . . . . . . . . . . . . . . . . . . . . . Rice . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oryza saliva . . . . . . . . . . . . . . . . . . . . . . . . Sand-bur . . . . . . . . . . . . . . . . . . . . . . . . Cenchrus tribulo-ides . . . . . . . . . . . . . . . . . Shallu . . . . . . . . . . . . . . . . . . . . . . . . . . . Andropogon sorghum . . . . . . . . . . . . . . . . Sorghum . . . . . . . . . . . . . . . . . . . . . . . . Andropogon sorghum . . . . . . . . . . . . . . . . Sor 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . Andropogon sorghum . . . . . . . . . . . . . . . . Spe t . . . . . . . . . . . . . . . . . . . . . . . . . . . Triticum satwum var. spella . . . . . . . . . . Sugar Cane . . . . . . . . . . . . . . . . . . . . . . Saccharum oflicinarum . . . . . . . .‘ . . . . . . . Wheat . . . . . . . . . . . . . . . . . . . . . . . . . . Triticum vulgare . . . . . . . . . . . . . . . . . . . . Wild Oat . . . . . . . . . . . . . . . . . . . . . . . . Avena fatua . . . . . . . . . . . . . . . . . . . . . . . . om >>> w>>wwn >>>> 0O >3’ UU>I>D>UU U >>>>>>>K>>>l>>>>1>i>>>>>>>>>>>>>>>>>i>i>> TEXAS RooT RoT. 23 Table 3. Relative resistance or susceptibility of various hosts to Texas root rot —Continued. _ _ Relative Common name Scientific name resistance or susceptibility Family Grossulariaceae. Currant . . . . . . . . . . . . . . . . . . . . . . . . . Ribes rubrum. . . . .~ . . . . . . . . . . . . . . . . . . A Gooseberry . . . . . . . . . . . . . . . . . . . . . . Ribes grossularia . . . . . . . . . . . . . . . . . . . . B Family Hamamelidaceae. _ _ i Gum . . . . . . . . . . . . . . . . . . . . . . . . . . . . Liquidambar styraciflua . . . . . . . . . . . . . . D Gum, Formosa . . . . . . . . . . . . . . . . . . . Liquidambar formosa . . . . . . . . . . . . . . . . D Family Iridaceae. Crocus . . . . . . . . . . . . . . . . . . . . . . . . . . Crocus spp . . . . . . . . . . . . . . . . . . . . . . . . . A Gladiolus . . . . . . . . . . . . . . . . . . . . . . . . Gladiolus spp . . . . . . . . . . . . . . . . . . . . . . . A Iris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Iris spp . . . . . . . . . . . . . . . . . . . . . . . . . . . . A (‘?) Family J uglandaceae. n ecan . . . . . . . . . . . . . . . . . . . . . . . . . . . Hicoria pecan._ . . . . . . . . . . . . . . . . . . . . . A ‘ Walnut, Black . . . . . . . . . . . . . . . . . . . Juglans nigra. . . . . . . . . . . . . . . . . . . . . . E Walnut, Japan . . . . . . . . . . . . . . . . . . . Juglans sieboldii . . . . . . . . . . . . . . . . . . C Family Labiatae. _ Basil, Sweet . . . . . . . . . . . . . . . . . . . . . Ocimum basilicum . . . . . . . . . . . . . . . . . . A Catnip . . . . . . . . . . . . . . . . . . . . . . . . . . Nepeta cataria . . . . . . . . . . . . . . . . . . . . . . A Mint . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mentha spicata . . . . . . . . . . . . . . . . . . . . . A Sage . . . . . . . . . . . . . . . . . . . . . . . . . . . . Salvia ofiicinalis . . . . . . . . . . . . . . . . . . . . A Savory, Summer . . . . . . . . . . . . . . . . . . Satureia hortensis . . . . . . . . . . . . . . . . . . A Family Leguminosae. _ _ _ Acacia . . . . . . . . . . . . . . . . . . . . . . . . . . Acacia nerifolia . . . . . . . . . . . . . . . . . . . . E Alfalfa . . . . . . . . . . . . . . . . . . . . . . . . . . Medicago saliva . . . . . . . . . . . . . . . . . . . . . D Alfalfa, German. . . ._. . . . . . . . . .. Medicago sp . . . . . . . . . . . . . . . . . . . . . . .. B Bean, allgarden varieties . . . . . . . . . . Phaseolus vulgaris . . . . . . . . . . . . . . . . . . C to D Bean, FPIJOlB . . . . . . . . . . . . . . . . . . . . . Phaseolus so .' . . . . . . . . . . . . . . . . . . . . . . D Bean, Jack . . . . . . . . . . . . . . . . . . . . . . Dolichos lablab . . . . . . . . . . . . . . . . . . . . . . C Bean, Japanese Sword . . . . . . . . . . . . Canavalia gladiata . . . . . . . . . . . . . . . . . . B Bean, Mexican Pinto . . . . . . . . . . . . . Phaseolus sp . . . . . . . . . . . . . . . . . . . . . E Bean, Mung . . . . . . . . . . . . . . . . . . . . . Phaseolus radiatus . . . . . . . . . . . . . . . . . . B Bean, Te ary . . . . . . . . . . . . . . . . . . . . Phaseolus lalifolius . . . . . . . . . . . . . . . . . . C Bean, Ve vet, var. Osceola . . . . . . . . . Stizolabium sp . . . . . . . . . . . . . . . . . . . . . . A Bean, Velvet, var. Speckled. . . . . . . . Stizolabium sp . . . . . . . . . . . . . . . . . . . . . . B Bean, Velvet, var. Bush . . . . . . . . . . . Stizolabium sp . . . . . . . . . . . . . . . . . . . . . . B Bean, Velvet, var. 100 Day . . . . . . . . Stizolabium sp . . . . . . . . . . . . . . . . . . . . . . B Bean, Velvet, var. Extra Early. . . . . Stizolabium sp . . . . . . . . . . . . . . . . . . . . . . B Bean, Velvet, var. Bunch . . . . . . . . . . Stizolabium sp . . . . . . . . . . . . . . . . . . . . . . B Cowpea. .r . . . . . . . . . . . . . . . . . . . . . . . Vigna sinensis . . . . . . . . . . . . . . . . . . . . . D Clover, Black Medic . . . . . . . . . . . . . . Medicago lupulina . . . . . . . . . . . . . . . . . . C Clover, Yellow Sweet . . . . . . . . . . . . . Melilotus ofiicinalis . . . . . . . . . . . . . . . . . C Clover, Sweet White . . . . . . . . . . . . . . Melilolus alba . . . . . . . . . . . . . . . . . . . . . . C Clover, Burr . . . . . . . . . . . . . . . . . . . Medicago obicularis . . . . . . . . . . . . . . . . . B Guar . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cyamopsis tetragonoloba . . . . . . . . . . . . . A to B Locust, Black . . . . . . . . . . . . . . . . . . . . Robinia pseucloacacia . . . . . . . . . . . . . . . . B Locust, Honey . . . . . . . . . . . . . . . . . . . Gleditsia triacanthos . . . . . . . . . . . . . . . . . B Pagoda Tree, Japanese . . . . . . . . . . . . Sophora Japonica . . . . . . . . . . . . . . . . . . . E Partridge Pea . . . . . . . . . . . . . . . . . . . . Casia chamaecrista . . . . . . . . . . . . . . . . . . C Pea, Garden . . . . . . . . . . . . . . . . . . . . . Pisum sativa . . . . . . . . . . . . . . . . . . . . . . . A to B Peanut . . . . . . . . . . . . . . . . . . . . . . . . . . Arachis hypogea . . . . . . . . . . . . . . . . . . . . B to C Soybean, Ito San . . . . . . . . . . . . . . . . . Glycine hispida . . . . . . . . . . . . . . . . . . . . . E Soybean, Duggar . . . . . . . . . . . . . . . . . Glycine hispida . . . . . . . . . . . . . . . . . . . ._ . E Soybean, Japanese Black . . . . . . . . . . Glycine hispida . . . . . . . . . . . . . . . . . . . . . E Vetch . . . . . . . . . . . . . . . . . . . . . . . . . . . Vicia spp . . . . . . . . . . . . . . . . . . . . . . . . . . A Sweet Pea . . . . . . . . . . . . . . . . , . . . . . . . Lathyrus odoratus . . . . . . ., . . . . . . . . . . . . A to B Wild Vetch . . . . . . . . . . . , . . . . . . . . . . Vicia angustifolia . . . . . . . . . . . . . . . . . . . C Family Liliaceae. Asparagus, Early Argentueil . . . . . . , Asparagus ofiicinalis . . . . . . . . . . . . . . . . A Asparagus, Palmeto . . . . . . . . . . . . . . . Asparagus ofiicinalis, . . . . . . . . . . . . . A Garlic, all varieties . . . . . . . . . . . . . . . Allium sp . . . . . . . . . . . . . . . . . . . . . . . . . . A Garlic, Wild. . . . . . . . . . . . . . . . . . . . . Allium canadense . . . . . . . . . . . . . . . . . . . A Hyacinth . . . . . . . . . . . . . . . . . . . . . . . . Hyacinthus orientalis . . . . . . . . . . . . . . . . A Leek . . . . . . . . . . . . . . . . . . . . . . . . . . . . Allium sp . . . . . . . . . . . . . . . . . . . . . . . . . . A Lily . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lilium longiflorum . . . . . . . . . . . . . . . . . . A Lily, Calla . . . . . . . . . . . . . . . . . . . . . . . .Araceae spp . . . . . . . . . . . . . . . . .~ . . . . . . . A Onion, Red Creole . . . . . . . . . . . . . . . . A.llium sp . . . . . . . . . . . . . . . . . . . . . . . . . . A Onion, Silverskin . . . . . . . . . . . . . . . . . Allium sp . . . . . . . . . . . . . . . . . . . . . . . . . . A Onion, Denver’s Yellow . . . . . . . . . . . Allium sp . . . . . . . . . . . . . . . . . . . . . . . . . . A Onion, Crystal Wax . . . . . . . . . . . . . . Allium sp . . . . . . . . . . . .' . . . . . . . . . . . . . . A Union, Shallot Ever reen . . . . . . . . . . Allium sp . . . . . . . . . . . . . . . . . . . . . . . . . . A Onion, tian, inter . . . . . . . . . . Allium sp . . . . . . . . . . . . . . . . . . . . . . . . . . A Onion, i . . . . . . . . . . . . . . . . . . . . . Allium vinale . . . . . .~ . . . . . . . . . . . . . . . . A Tulip . . . . . . . . . . . . . . . . . . . . . . . . . Tulipa spp . . . . . . . . . . . . . . . . . . . . . . . . . A Yucca . . . . . . . . . . . . . . . . . . . . . . . . . . . Yucca filamentosa . . . . . . . . . . . . . . . . . . . A 24. Table 3. BULLETIN N0. 307. Continue . Relative resistance or susceptibility of various hosts to Texas root rot Common name Scientific name Family Magnoliaceae. _ agn ia . . . . . . . . . . . . . . . . . . . . . . . . Magnolia grandiflora . . . . . . . . . . . . . . . . Tulip Tree . . . . . . . . . . . . . . . . . . . . . . . Lirzodendron lulipefera . . . . . . . . . . . . . . Family Malvaceae. _ A t ea . . . . . . . . . . . . . . . . . . . . . . . . . . Hibiscus syriacus . . . . . . . . . . . . . . . . . . . Bladder Ketmia . . . . . . . . . . . . . . . . . . Hibiscus trionum . . . . . . . . . . . . . . . . . . . Cotton . . . . . . . . . . . . . . . . . . . . . . . . . . Gossypium spp . . . . . . . . . . . . . . . . . . . . . . Hollyhock._ . . .. . . . . . . . . . . . . . . . . . . . Althea rosea . . . . . . . . . . . . . . . . . . . . . . . . Mallow, High . . . . . . . . . . . . . . . . . . . . Malva sylveslris . . . . . . . . . . . . . . . . . . . . . allow, L_ow . . . . . . . . . . . . . . . . . . . . M alva rolundi olia . . . . . . . . . . . . . . . . . . Okra, White Velvet . . . . . . . . . . . . . . . Hibiscus escu entis . . . . . . . . . . . . . . . . . Okra, Dwarf Green . . . . . . . . . . . . . . . Hibiscus esculenlis . . . . . . . . . . . . . . . . . . Sida . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sida hederacea . . . . . . . . . . . . . . . . . . . . . . Sida . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sida spinosa . . . . . . . . . . . . . . . . . . . . . . . Star Mallow . . . . . . . . . . . . . . . . . . . . . M alvaslrum coccinum . . . . . . . . . . . . . . . . Velvet Leaf . . . . . . . . . . . . . . . .' . . . . . . Abutzlon avicennae . . . . . . . . . . . . . . . . . . Famil Meliaccae. _ . C ina Berry Tree . . . . . . . . . . . . . . . . Melza azedarach. . . . . . . . . . . . . . . . . . . . Family Moraceae. _ Fig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ficus carica. . . . . . . . . . . . . . . . . . . . . . . Mulberry . . . . . . . . . . . . . . . . . . . . . . . . M orus lartarica . . . . . . . . . . . . . . . . . . . . . Osage Orange . . . . . . . . . . . . . . . . . . . . Toxylan pomiferum . . . . . . . . . . . . . . . . . Family Myctaginaceae. _ _ Four-O’Clock . . . . . . . . . . . . . . . . . . . . Mzrabilis Jalapa . . . . . . . . . . . . . . . . . . . Family Myriaceae. _ _ Crape Myrtle . . . . . . . . . . . _. . . . . . . . . Myrzca cerifera . . . . . . . . . . . . . . . . . . . . . Family M yrlaceae. _ Pomegranate . . . . . . . . . . . . . . . . . . . . . Pumica granatum . . . . . . . . . . . . . . . . . . . Family Oleaceae. _ _ Ash, American White . . . . . . . . . . . . . Fraxznus americana . . . . . . . . . . . . . . . . . Ash, Green . . . . . . . . . . . . . . . . . . . . . . Fraxinus lanceolala . . . . . . . . . . . . . . . . . Privet . . . . . . . . . . . . . . . . . . . . . . . . . . . Lzguslrum spp . . . . . . . . . . . . . . . . . . . . . . Family Oxalidaceae. xalis . . . . . . . . . . . . . . . . . . . . . . . . . . . Oxalis bowiei . . . . . . . . . . . . . . . . . . . . . . . Sorrel, Wood . . . . . . . . . . . . . . . . . . . . . Oxalis violacea . . . . . . . . . . . . . . . . . . . . . . Sorrel, Sheep . . . . . . . . . . . . . . . . . . . Rumex acetosella . . . . . . . . . . . . . . . . . . . . Family Polemoniaceae. Phlox . . . . . . . . . . . . . . . . . . . . . . . . . . . Phlox drummondii . . . . . . . . . . . . . . . . . . Family Polygonaceae. Rhubarb . . . . . . . . . . . . . . . . . . . . . . . . Rheum oflicinale . . . . . . . . . . . . . . . . . . . . Family Primulaceae. Primrose . . . . . . . . . . . . . . . . . . . . . . . . Primula vulgaris . . . . . . . . . . . . . . . . . . . . Family Ranuriculaceae. Larkspur. . . . .. . Delphinium, sp.. . . . . . . . .. Family Rhamnaceae. _ Jujube, T. S. 5095 . . . . . . . . . . . . . . . Zizyphus saliva . . . . . . . . . . . . . . . . . . . . . J ujube, T. S. 36854 . . . . . . . . . . . . . . . Zizyphus saliva . . . . . . . . . . . . . . . . . . . . . Jujube, T. S. 38245 . . . . . . . . . . . . . . . Zizyphus saliva . . . . . . . . . . . . . . . . . . . . . Jujube, T. S. 22686 . . . . . . . . . . . . . . . Zizyphus saliva . . . . . . . . . . . . . . . . . . . . . Jujube, T. S. 38249 . . . . . . . . . . . . . . . Zizyphus saliva . . . . . . . . . . . . . . . . . . . . . Family Rosaceae. pp . . . . . . . . . . . . . . . . . . . . . . . . . . . Pyrus malus . . . . . . . . . . . . . . . . . . . . . . . Blackberry, Dallas . . . . . . . . . . . . . . . . Rubus sp . . . . . . . . . . . . . . . . . . . . . . . . . . . Dewberry, Austin Mays . . . . . . . . . . . Rubus sp . . . . . . . . . . . . . . . . . . . . . . . . . . .. Dewberry, Louisiana . . . . . . . . . . . . . . Rubus sp . . . . . . . . . . . . . . . . . . . . . . . . . . . Dewberry, Haupt . . . . . . . . . . . . . . . . Rubus, sp . . . . . . . . . . . . . . . . . . . . . . . . . . Peach . . . . . . . . . . . . . . . . . . . . . . . . . . . Prunus persica . . . . . . . . . . . . . . . . . . . . . Pear . . . . . . . . . . ._ . . . . . . . . . . . . . . . . . Pyrus communis . . . . . . . . . . . . . . . . . . . . Raspberry, Cordial . . . . . . . . . . . . . . . Rubus slrlgosus . . . . . . . . . . . . . . . . . . . . . ose . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rosa spp . . . . . . . . . . . . . . . . . . . . . . . . . . . Spiraea . . . . . . . . . . . . . . . . . . . . . . . .. Spiraea- spp, . . ._ . . . . . . . . . . . . . ..~.... Strawberry, Lady Thomson . . . . . . . . Fragaria chiloensis . . . . . . . . . . . . . . . . . . Strawberry, Aroma . . . . . . . . . . . . . . . Fragaria‘ chiloemis . . . . . . . . . . . . . . . . . . Strawberry, Klondike . . . . . . . . . . . . . Fragaria chiloemus . . . . . . . . . . . . . . . . . . Relative resistance _or susceptibility W?’ O EDWOOUUUUWUUUO > I>UU D> f> I>I>I> UUJU I> >>>wnomw>>>>u UUOOO TEXAS Room Rom. 25 Table 3. Relativefiesistance or susceptibility of various hosts to Texas root rot —Cont1nued. _ _ _ Relative Common name Scientific name resistance or susceptibility Family Rubuceae. Cape Jasmine . . . . . . . . . . . . . . . . . . . . Family Salicaceae._ Poplar, Carolina . . . . . . . . . . . . . . . . . . Poplar, Lombardy . . . . . .‘ . . . . . . . . . . Poplar, Norwegian . . . . . . . . . . . . . . . . Willow . . . . . . . . . . . . . . . . . . . . . . . . . . Family Sapinciaceae. B loon Vine . . . . . . . . . . . . . . . . . . . . . Family Scrophulariaceae. Snapdragon . . . . . . . . . . . . . . . . . . . . . . Family Solanaceae. Buffalo-Bur . . . . . . . . . . . . . . . . . . . . . . Bull Nettle . . . . . . . . . . . . . . . . . . . . . . Eggplant, Spineless . . . . . . . . . . . . . . . Pepper; B_ull Nose . . . . . . . . . . . . . . . Pepper, Pimento. ._ . . . . . . _. . . . . . . . . Pepper, Chinese _Giant . . . . . . . _. . . . . Pepper, Ruby King . . . . . . . . . . . . . . . Pepper, Long Red Cayenne . . . . . . . . Petunia. ._ . . . . . . . . . ._ . . . . . . . . . .. Potato (Irish) all varieties) . . . . . . . . Tobacco . . . . . . . . . . . . . . . . . . . . . . . . . Tomato . . . . . . . . . . . . . . .' . . . . . . . . . . Family Sierculiaceae. _ Varnish Tree, Chinese. . . . . . . Family Tamaricaceae. Tamarisk, Common . . . . . . . . . . . . . . . Family Ulmaceae. , Elm, Cork Elm, Native . . . . . ._ . . . . . . . . . . . . . . . Elm, American White . . . . . . . . . . . . . Hackberr _ Hackberry, Chinese . . . . . . . . . . . . . ., Family Umbelliferae. Anise . . . . . . . ._ . . . . . . . . . . . . . . . . . Carrot, all varieties . . . . . . . . . . . . . . . Chervil. ., . . . . . . . . . . . . . . .- . . . . . . . . Dill . . . . . . . ._ . . . . . . . . . . . . . . . . . . . . . Fennel, Italian. . . . ." . . . . . . . . . . . . . . Fennel, Sweet . . . . . . . . . . . . . . . . . . . . Parsley, Plain . . . . . . . . . . . . . . . . . . . . Parsley, Double Curled. . . . . . . . . . . . Parsley, Curled . . . . . . . . . . . . . . . . . . Parsaip, Imperial Hallow . . . . . . . . . . o u a o o u - - - - - Q - - - - - - - . . - n n n u Q Q » - - - » ¢ ¢ | - ¢ - - - - - 0 - Family Urticaceae. Hemp, Kymington . . . . . . . . . . . . . . . 'amily Vaccinaceae. Cranberry, Small . . . . . . . . . . . . . . . . . Cranberry, Large . . . . . . . . . . . . . . . . . Family Valerianceae. ~ Corn, Salad . . . . . . . . . . . . . . . . . . . . . . Family Violaceae. Gardenia veitchii . . . . . . . . . . . . . . . . . . . . Populus eugenia . . . . . . . . . . . . . . . . . . . . Populus nigraitalica . . . . . . . . . . . . . . . . . Populus sp . . . . . . . . . . . . . . . . . . . . . . . . . Salix nigra . . . . . . . . . . . . . . . . . . . . . . . . Cardiospermum halicacabum . . . . . . . . . . Antirrhinum majus . . . . . . . . . . . . . . . . . Solarium rostratum . . . . . . . . . . . . . . . . . . Solarium elaeangifolium . . . . . . . . . . . . . . Solarium melongena . . . . . . . . . . . . . . . . . Capsicum annum . . . . . . . . . . . . . . . . . . . Capsicum annum . . . . . . . . . . . . . . . . . . . Capsicum annum . . . . . . . . . . . . . . . . . . . Capsicum annum . . . . . . . . . . . . . . . . . . . Capsicum annum; . . . . . . . . . . . . . . . . . . Petunia sp . . . . . . . . . . . . . . . . . . . . . . . . . Solarium tuberosum . . . . . . . . . . . . . . . . . N icotiana tabacum . . . . . . . . . . . . . . . . . . Lycopersicum esculentum . . . . . . . . . . . . . . Sterculia platanifolia . . . . . . . . . . . . . . . . Tamarizi: gallica . . . . . . . . . . . . . . . . . . . . Ulmus racemosa . . . . . . . . . . . . . . . . . . . . Ulmus virginiana . . . . . . . . . . . . . . . . . . . Ulmus Americana . . . . . . . . . . . . . . . . . . Celtis occidentalis . . . . . . . . . . . . . . . . . . . Celtis chinensis . . . . . . . . . . . . . . . . . . . . . Pimpinella anisum . . . . . . . . . . . . . . . . . . Daucus carota . . . . . . . . . . . . . . ., . . . . . . . Anthriscus cerefolium . . . . . . . . . . . . . . . . Anethum graveolens . . . . . . . . . . . . . . . . . Foeniculum vulgare . . . . . . . . . . . . . . . . . . Foeniculum ofiicinale . . . . . . . . . . . . . . . . Petroselinum hortense . . . . . . . . . . . . . . . . Petroselinum hortense . . . . . . . . . . . . . . . . Petrqselinum hortense . . . . . . . . . . . . . . . . Pastinaca sativa . . . . . . . . . .- . . . . . . . . . . Cannabis saliva . . . . . . . . . . . . . . . . . . . . . Vaccinium oxycoccus . . . . . . . . . . . . . . . . Vaccinium macrocarpon . . . . . . . . . . . . . Valerianella olitaria . . . . . . . . . . . . . . . . . Viola tricolar . . . . . . . . . . . . . . . . . . . . . . . Viola odorata . . . . . . . . . . . . . . . . . . . . . . . i> > UJOUU 11> U W>I>>OOOOOO>> O On U >> > >> U 03o3>>>>3> >>w>w no m 2-6 BULLETIN N0. 307. IS THERE A DIFFERENCE IN RESISTANCE IN DIFFERENT VCARIETIES? It has already been shown in Table 3 that certain hosts seem to resistant, while others are either slightly 0r entirely susceptible to thejl; Texas root rot disease. During the course of this work, we felt it i‘. necessary to determine if possible whether 0r not there actually exists a definite resistance in different varieties of the same species and genusfi Accordingly, tests were made with various field crops, chief of which were cotton, okra, and certain legumes. In referring to Table 4, one sees that of the cotton varieties tested during 1919, which was really a very favorable year for Texas root’ rot, it seems that there is prob-i; ably a difference in resistance of some of the cotton varieties. however, cannot be stated with certainty unless these trials are re- j peated for a number of years, which, because of lack of funds and lack a of sufficient land, we were forced to discontinue for the present at least. What is true of cotton seems also to apply to the legumes tested, as shown in Table 4. Table 4i Susceptibility of some legume and cotton varieties—1919. This, _ Total _ Total Host and name of variety per cent Host and name of variety per cent s, root rot root rot z i Cotton v Legumes 1i Bank Account . . . . . . . . . . . . . . . . . . . . . 43 CowpeaflGroit) . . . . . . . . . . . . . . . . . . 31 i5 Matchless (extra early big boll) . . . . . . 37 Cowpea (U right) . . . . . . . . . . . . . . . . 40 g} Broadwell’s Double-jointed . . . . . . . . . . 4O Cowpea (C ay) . . . . . . . . . . . . . . . . . . . 33 Allen’s Express . . . . . . . . . . . . . . . . . . .. 46 Cowpea (Iron crossed with black- Early King . . . . . . . . . . . . . . . . . . . . . . . 30 eyedlpea) . . . . . . . . . . . ._ . . . . . . . 37 .3 Sure _Crop . . . . . . . . . . . . . . . . . . . . . . . . 65 Cowpea Slron crossed with whip- 5 Hasting’s Upright . . . . . . . . . . . . . . . . . . 55 poor-wi l) . . . . . . . . . . . . . . . . . . . . . .34 Union Big Boll . . . . . . . . .' . . . . . . . . . . . 55 Cowpea (Red Ripper) . . . . . . . . . . . . . 45 Belton-Rowden . . . . . . . . . . . . . . . . . . . . 55 Cowpea (Brabham) . . . . . . . . . . . . . . . 45 Belton-Rowden . . . . . . . . . . . . . . . . . . 80 Cowpea (Iron) . . . . . . . . . . . . . . . . . . . 38 Rowden . . . . . . . . . . ; . . . . . . . . . . . . . . . 60 Cowpea (New_ Era) . . . . . . . . . . . . . . . 31 Cleveland . . . . . . . . . . . . . . . . . . . . . . . . . 65 Soy- ean (Ohio grown) . . . . . . . . . . . . 60 Cook's Silk . . . . . . . . . . . . . . . . . . . . . . . 70 Soy-bean (Ito San) . . . . . . . . . . . . . . . _ 75 Mebane . . . . . . . . . . . . . . . . . . . . . . . . . . 43. Soy-bean (Ebony) . . . . . . . . . . . . . . . . 90 Mebane. ., . . . . . . . . . . . . . . . . . . . . . . . . 40 Yokahoma Bean . . . . . . . . . . . . . . . . . . 18 Peterkin . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Velvet Bean . . . . . . . . . . . . . . . . . . . . . 15 Cleveland Big Boll . . . . . . . . . . . . . . . . . 34 Befri (Origin, British India) . . . . . . . 22 oykin . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 uar . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Cotton (Belton) . . . . . . . . . . . . . . . . . . . 51 Peanut (Tenn_. Red) . . . . . . . . . . . . . 23 Peanuts (Spanish) . . . . . . . . . . . . . . . . 13 Peanuts (Valencia Improved) . . . . . . 16 As concerns the fruit trees, there seems to be no difference in sus-i ceptibility between various varieties. varieties of pears and six varieties of apples seem to show that they are all equally susceptible and that fruit trees when planted usually begin to die the very first year they are put out. Dying becomes more pronounced as the years succeed each other and as the dead trees replaced by healthy ones the following season. catedin Tables 5 and 6, which are self-explanatory and which show that wherever a pear or an apple tree dies from the Texas root rot disease no other pear or apple tree should follow in the same place? until all living carriers are eliminated, as it will likely die either the? same season in which it it put out, or after two or three years at the most. Trials made with five different This is clearly indi- TEXAS R001: R01‘. 27 Table 5." Susceptibility of pears to Texas root rot. _ Plat and i Name of variety No. of Year Year Year Year Year tree planted killed killed killed killed {iefier . . . . . . . . . . .1 . . . . . . . . . . . . . 1 1917 1919* 1920* 1921 . . . . . . .. Kieffer . . . . . . . . . . . . . . . . .’ . . . . . . . 2 1917 1919* 1920* 1921 . . . . . . .. {iefier . . . . . . . . . . . . . . . . . . . . . . . . 3 1917 1919* 1920* 1921 . . . . . . .. Kiefier . . . . . . . . . . . . . . . . . . . . . . . A 4 1917 1919* 1920* 1921 . . . . . . . . Kieffer . . . . . . . . . . . . . . . . . . . . . . .. 5 1917* 1918* 1919*. 1920* 1921 fiieffer . . . . . . . . . . . . . . . . . . . . . . . . 6 1917* 1918* 1919* 1920* 1921 Kieffer . . . . . . . . . . . . . . . . . . . . . . . . 7 1917* 1918* 1919* 1920* 1921 Kieffer . . . . . . . . . . . . . . . . . . . . . . . . 8 1917* 1918* 1919* 1920* 1921 Kieffer . . . . . . . . . . . . .., . . . . . . . . .. 9 1917 1919* 1920* 1921* . . . . . . . . Kieffer . . . . . . . . . . . . . . . . . . . . . . .. 10 1917* 1919* , 1920* 1921* 1921 Kieffer . . . . . . . . . . . . . . . . . . . . . . . . 11 1917* 1921 l . . . . . . . . . . . . . . . . . . . . . . . . Kieffer . . . . . . . . . . . . . . . . . . . . . . . . 12 1917 1919* 1920* 1921 . . . . . . .. Kieffer . . . . . . . . . . . . . . . . . . . . . . .. 13 1917 1919* 1920* 1921 . . . . . . . . Kieffer . . . . . . . . . . . . . . . . . . . . . . . . 14 1917 1921 . . . . . . . . . . . ." . . . . . . . . . . . . Kieffer . . . . . . . . . . . . . . . . . . . . . . .. 15 1917 1919* 1920* 1921 i . . . . . . . . Kieffer . . . . ..‘ . . . . . . . . . . . . . . . . .. 16 1917 1920* 1921 . . . . . . . .1 . . . . . . .. Kieffer . . . . . . . . . . . . . . . . . . . . . . . . 17- 1917 1919* 1920* 1921 i . . . . . . . . Kieffer . . . . . . . . . . . . . . . . . . . . . . . . 18 1917* 1919* l 1920* 1921 i . . . . . . . . Bartlett . . . . . . . . . . . . . . . . . . . . . . . 1 1917 1919* 1920* 1921 . . . . . . . . 2 1917 1918* 1921 . . . . . . . . . . . . . . . . 3 1917 1918* 1919* 1920* 1921* 4 1917 1919* 1921 . . . . . . . . . . . . . . . . 1 1917 1918* 1919* 1920* 1921* 2 1917 1920* 1921 . . . . . . . . . . . . . . . . 3 1917 1919* 1920* 1921 . . . . . . . . 4 1917 1921 . . . . . . . . . . . . . . . . . . . . . . . . 1 1917 1918 1919* 1920* 1921 2 1917 1919* 1920* 1921 . . . . . . . . 3 1917 1918* I 1919* 1920* 1921 4 1917 1918* 1919* 1920* 1921 1 1917 1918* l 1919* 1920* 1921* 2 1917 1919* 1920* 1921 . . . . . . . . 3 1917 1919* 1920* 1921 . . . . . . . . » 4 1917 1919* 1920* . . . . . . . . . . . . . . . . *Trees died that year and were replaced by the same variety the following spring. Table 6. Susceptibility of apples to Texas root rot_ _ Plat and I " i Name of variety No. of Year Year Year Year Year tree planted killed killed killed killed Arkansas Black . . . . . . . . . . . . . . . . 1 1917 1918* i 1919* 1920* 1921 Arkansas Black . . . . . . . . . . . . . . . . 2 1917 1918* 1919* 1920* ,1921 Arkansas Black . . . . . . . . . . . . . . . . 3 1917 1918* 1919* 1920* 1921 Arkansas Black . . . . . . . . . . . . . . . . 4 1917 1918* 1919* 1920* 921 Arkansas Black . . . . . . . . . . . . . . . . 5 1917 1919* 1920* 1921 . . . . . . . . Arkansas Black . . . . . . . . . . . . . . . . 6 1917 1919* 1920* 1921 . . . . . . . . Ben Davis . . . . . . . . . . . . . . . . . . . . . 1 1917 1919* 1920* 1921 . . . . . . . . Ben Davis . . . . . . . . . . . . . . . . . . . . . 2 1917 1921 . . . . . . . . . . . . . . . . . . . . . . . . Ben Davis . . . . . . . . . . . . . . . . . . . . . 3 1917 1918* 1919* 1920* 1921 Ben Davis . . . . . . . . . . . . . . . . . . . . . 4 1917 1919* 1920* 1921 . . . . . . . . Ben Davis . . . . . . . . . . . . . . . . . . . . . 5 1917 1919* 1920* 1921 . . . . . . . . Ben Davis . . . . . . . . . . . . . . . . . . . . . 6 1917 1918* 1919* 1920* 1921 Junuuer Queen . . . . . . . . . . . . . . . . . 1 1917 1918* 1919* 1920* 1921 Jiummer Queen . . . . . . . . . . . . . . . . . 2 1917 1919* 1920* 1921 . . . . . . . . I§>ummer Queen. . .- . . . . . . , . . . . . . . 3 1917 1918* 1919* 1920* 1921 Igiummer Queen . . . . . . . . . . . . . . . . . 4 1917 1918 919* 1920* 1921 Summer Queen . . . . . . . . . . . . . . . . . 5 1917 1919 1920* 1921 . . . . . . . . Summer Queen . . . . . . . . . . . . . . . . . 6 1917 L921 . . . . . . . . . . . . . . . . . . . . . . . . Kinard Choice . . . . . . . . . . . . . . . . . 1 1917 1919* 1920* 1921 . . . . . . . . Kinard Choice . . . . . . . . . . . . . . . . . 2 1917 1919* 1920* 1921. . . . . . . . . Klnard Choice. . . . . . . . . . . . . . . .. 3 1917 1919* 1920* 1921 . . . . . . .. Kinard Choice . . . . . . . . . . . . . . . . . 4 1917 1918* 1919 1920* 1921 Kinard Choice . . . . . . . . . . . . . . . . . 5 1917 1918* 1919 1920 1921 Kinard Choice . . . . . . . . . . . . . . . . . 6 1917 1918* i 1919* 1920* . . . . . . .. Red June . . . . . . . . . . . . . . . . . . . . . . 1 1917 1919* 1920* 1921 1921 Red June . . . . . . . . . . . . . . . . . . . . .. 2 1917 1918* 1919* 1920* 1921 Red June . . . . . . . . . . . . . . . . . . . . . . 3 1917 1919* 1920* 1921 . . . . . . . . Red June . . . . . . . . . . . . . . . . . . . . .. 4 1917 1918* 1919* 1920* 1921 Red June . . . . . . . . . . . . . . . . . . . . .. 5 1917 1918* 1919* 1920* 1921 Red June . . . . . . . . . . . . . . . . . . .. 6 1917 1919* 1920* 1921 . . . . . . . . Yellow Transparent . . . . . . . . . . . . . 1 1917 1919* 1920* 1921 . . . . . . . . Yellow Transparent . . . . . . . . . . . . . 2 1917 1918* 1919* 1921 i . . . . . . . . Yellow Transparent. , . . . . . . . . . . . 3 1917 1919* 1920* 1921 . . . . . . . . Yellow Transparent . . . . . . . . . . . . 4 1917 1918* 1919* 1920* 1921 Yellow Transparent . . . . . . . . . . . . . 5 1917 1919* 1920* 1921 . . . . . . . . Yellow Transparent . . . . . . . . . . . . . 6 1917 1920* 1921 . . . . . . . . . . . . . . . . *Trees died. that year and were replaced by the same variety the following spring. .28 BULLETIN N0. 307. It should be added that where the- pear and apple varieties were planted as indicated in Tables 5 and 6, cotton was grown between the trees for a number of years in succession; and each year the cotton in the same orchard died from the Texas root rot. Furthermore, none of the living cotton roots were pulled out, but were allowed to remain in the soil during the Winter; thus the Texas root rot fungus had a chance to pass over winter "on those cotton roots which escaped sum- mer infection and which remained alive during the Winter months. Likewise, no attempt was made to kill out the roots of the small- flowered pink morning glory (I pomoea trichocarpa). From these roots evidently the Texas root rot fungus passed over to the roots of the pear and apple trees. ARE THERE ANY RESISTANT STRAINS? Cotton growers are well aware of the fact that where the Texas root rot disease is very prevalent in any one cotton field the disease usually works in more or less definite spots, sometimes killing every plant within the infected area. At other times, however, there are healthy plants standing up here and there in close proximity to plants that have died of infection. Frequently it is seen that when several cotton plants grow together in the same hill one may remain alive while all the others near or next to it will die from the Texas root rot disease. It, therefore, occurred to the writers that there might possibly be a certain inherent resistance in those individual cotton plants which seem to stand up while others succumb. Accordingly, a large quantity of seed.from individual cotton plants apparently resistant was selected and planted in a field known to be badly infected with the Texas root rot disease. Side by side with that, seeds from unselected plants were planted in the same field as checks for comparison. These tests were carried on for a period of four years with the result, apparently, that the plants from the selected strains were no more resistant than those that came from the check or unselected plants. On the other hand, the amount of root rot in both selected and resistant strains seemed to have been determined primarily by the amount of rainfull during the season. This is clearly shown in Table '7, which indicates that during 1918, which was a dry year, there was practically no root rot present in either of the strains of cotton whether coming from seeds of healthy but ‘non-selected plants, or those coming from seeds of plants killed by root rot, or those which were selected for ap- parent resistance. Likewise, during 1919, which was a very wet sum- mer, the amount of root rot depended primarily upon the rainfall, and upon the incidental appearance of root rot spots where the selected and unselected cotton seed were planted. ‘ ' From Table 7, it seems evident that it is apparently useless to try to-select a cotton which is altogether immune to the disease. However, inasmuch as there seems to be certain cotton plants or strains which do stand up and escape root rot infection during the summer months, it becomes therefore apparent that it may be possible to select such strains as are able to withstand the disease the longest time during TEXAs R001‘ Rom. 29 the season. In other words, those strains which become infected very late in the season may be those worthy of promise, in the sense that cotton strains may be developed through selection that would take the root rot very late, in which case the crop would practically mature and be unhurt by the disease. Table 7. Susceptibility offselected cotton strains. l Total per cent. Source of seed for planting Year l root rot l Sept. 25. Belton cotton—healthy plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 None Belton cotton——killed by root rot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 None Belton cotton-apparently resistant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 None Mebane cotton—healthy plants . . . . . . . . . . . . . . . . . . . . . . . . . . . ; . . . . . . . 1918 None Mebane cotton—plants killed by root rot . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 None Mebane cotton——apparently resistant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 None Rowden cotton—healthy plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 None Rowden cotton-plants killed by root rot . . . . . . . . . . . .\ . . . . . . . . . . . . . . 1919 None Rowden cotton—apparently resistant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 None Belton cotton——healthy plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 8O Belton cotton—killed by root rot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 3 Belton cotton——apparently resistant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 3 Belton cotton—apparently resistant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 6O Belton cotton—healthy plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 2O Mebane cotton—healthy plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 24 Mebane cotton—plan'ts killed by root rot . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 43‘ Mebane ootton—apparently resistant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 y 17 l DOES A SUSOEPTIBLE CROP ONE YEAR INFLUENCE THE AMOUNT OF ROOT ROT IN ANOTHER SUSOEPTIBLE CROP THE NEXT YEAR? It has been observed repeatedly that year in and year out certain crops seem to be more susceptible to the Texas root rot disease than others. For instance, sweet potatoes when grown in infected land will yield a larger percentage of diseased hills than a similar field planted to cotton. The reason, it seems, is probably the fact that when plants of a certain crop are grown close together in the same hill, as is the case with the sweet potato, carrots, and beets, which are planted close in the row, they are more susceptible to root rot than plants which require more spacing. With this in mind, it was desir- able to determine what would be the effect of planting cotton, for. in- stance, following a very susceptible crop like the sweet_ potato. Al- though this test was carried out during 1917 and 1918, both very dry years, in which cotton root rot was very limited, it was nevertheless found that a very susceptible crop like the sweet potato decidedly in- creased the root rot in cotton when the latter followed the sweet pota- toes, but that was apparently not the case when sweet potatoes fol- lowed cotton. This is well shown in Table 8, which is self-explanatory. From this table it is seen that the sweet potato in 1917 in the trial plat showed a total of 41 per cent. infection from root rot. In 1918, when cotton followed in place occupied by sweet potatoes in 1917, the total per cent. of root rot was 52 as compared to 22 per cent. for the cotton check in 1917, and 5 per cent. for the cotton check in 1918. Likewise, when cotton was grown in an experimental plat in 1917, the total per cent. of root rot that year was only 14. When this same 30 . BULLETIN N0. 307. place was occupied by sweet potatoes in 1918, the total per cent. of root rot that year was 14., indicating that there Was no increase of root rot in sweet potatoes due to the cotton previously grown in the same plat. While the figures in Table 8 are at best only indicative, they seem to have a practical application. The up-to-date cotton grower will take every precaution to prevent planting his cotton after those crops which are known to be highly susceptible to root rot. Of such crops may be mentioned the sweet potato, alfalfa, or sweet clover, which are excellent carriers of the Texas root rot during the winter months. ~ Table 8. Effect of root rot from one susceptible crop one year on another susceptible crop the following year. Total Date counted, per cent root rot per Host Year cent ;June 25, July 10, July 30, Aug. 15 Sept. 10, Oct. l, root i 1917 1917 1917 1917 , 1917 1917 rot Sweet potato . . . . . . . . 1917 None 3 6 7 12 13 4'1’ (Nancy Hall) June 25, July 10, July 30, Au . 15, Sept. 10, Oct. 1, 1918 1918 1918 1 18 1918 1918 Cotton (Belton). . . . . 1918 2 5 8 1O 12 15 52 _ June 25, Julg 1o, Julg 3o, Au .15, Sept. 10, Oct. 1, 1917 1 17 1 17 1 17 1917 1917 Cotton (Check). . . . . 1917 None None 1 4 9 22 (Belton) June 25, Julg 10, Julg 30, Au . 15, Sept. 10, Oct. 1, 1918 1 18 1 18 1 18 1918 1918 Cotton (Check). . . . . 1918 None None None 1 2 2 5 (Belton) June 25, July 10, Julg 30, Aug. 15, Sept. 10, Oct. 1, 1917 1917 l 17 1 17 1917 1917 Cotton (Belton). . . . . 1917 None None 1 2 5 6 14 June 25, Julg 10, July 30, Aug. 1 5, Sept. 10, Oct. 1, 1918 1 18 1918 1918 1918 1918 Sweet potato. . . .. 1918 1 1 5 3 2 2 14 (Nancy Hall) CONDITIONS FAVORING OR RESTRICTING THE SPREAD OF TEXAS ROOT ROT. From a practical consideration it is necessary that we have informa- tion on the conditions which favor the spread or restriction of the Texas root rot disease. Various observations and studies were made in order to determine more or less definitely what these conditions were. These studies were made on cotton and also on a small scale on the okra. Whether the same results would apply to other crops, especially trees, as they are subject to the Texas root rot disease, is as yet difficult to foretell. Effect of Climate on Texas Root Rot. Climatic conditions are im- portant factors in restricting or increasing the spread of the Texas root rot disease. Other things being equal, the disease is more prevalent in some years than in others. This prevalence or absence seems to a great extent determined not only by soil ‘conditions, but also to a large i TEXAS Roor Rom. 31 extent by climatic conditions during the summer season and by the number of winter carriers permitted to live over in the soil. Repeated observations and statements by progressive farmers have indicated that the damage from the Texas root rot disease, other things being equal, is far more serious during wet than during dry seasons (see Tables 9, 10, and 12). Percentages of root rot counts were made by the writers in several cotton and okra fields during a period of six years with the result that the average of these counts clearly indicates the greater preponderance of root rot during a Wet summer over the dry one. This is shown in Table 9, which is a typical sample of Wet years. During the dry season of 1918, the percentage of root rot ‘with okra varied from one to three per cent., and in 1919, a wet season, the percentage of root rot varied from 66 to 83 per cent. What is true with okra also holds with cotton and other crops of a similar root system. Table 9. Root rot as affected by seasonal differences. Total a per cent Host Year of root rot ' Sept. 30. Okra (White Velvet) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 2 Okra (Perkin’s Long Pod) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 1 .5 Okra (Dwarf Green) .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 3 Okra (Dwarf Whit . . ._ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 2 Okra (Kleckley’s Favorite) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1918 Okra (White Velvet) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 66 Okra (Perkin’s Perfect, Long Pod) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 82 Okra (Dwarf Green) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 75 Okra (Dwarf White) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 66 Okra (Kleckley’s Favorite) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 79 Okra (Kleckley’s Giant) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1919 83 Efiect 0f Irrigation 0n Texas Root Rot. It has already been indi- cated in Table 9 that the Texas root rot disease is far more prevalent and more serious during a wet summer than during a dry one. Rains during June and July invariably bring out more root rot than if these two months were comparatively dry. This, then, seems to indicate that the presence of moisture during these months is an important factor in favoring a better root system and hence in insuring under- ground contact, which seems to favor the spread of the Texas root rot disease. In order to make more certain of this, experiments were carried out during several years with a view of determining the effect of irrigation in favoring or restricting Texas root rot during dry and wet summers. The irrigations were tried on okra and cotton, both of which are susceptible hosts. From one to four irrigations were given in order to determine whether frequent waterings will mean increased percentages of the disease. The results are indicated in Table ~10. From this table it is seen that in 1918, which was a dry year, the okra check which had no irrigation showed a total of only 6 per cent. of Texas root rot that year and likewise the cotton check with no irrigation, a total of 2 per cent. of root rot. On the other hand, one irrigation increased the total percentage of root rot on okra to 15 per cent. and on cotton to 6 per cent. Three irrigations in- creased the total percentage of root rot in okra to 23 and in cotton 32 a BULLETIN N0. 307. to 25 per cent. Four irrigations increased the total percentage of root rot in okra to 49 and in cotton to 1'7, apparently, a decrease over the three irrigations in cotton. Nevertheless, it is very evident that during a dry year when moisture is artificially added to the soil, Texas root rot increases in proportion as the number of irrigations is in- creased. Similarly, in 1919, which was a wet year, the check plat of okra which received no irrigation gave a total percentage of 66% per cent. of root rot, whereas ‘one watering increased the total percentage of root rot to 83 per cent. This clearly indicates that even in a wet year when root rot is prevalent, the addition of more water in the form of irrigation will make it still more so. From these experiments it seems plainly established that moisture is one of the important fac- tors in favoring the spread of Texas root rot. 33 TEXAS R001" R012 2.02020 2Q. 2015002 02 2002220220: 0: 2.002. n0». 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It became evident that it was necessary to determine the effect of both the air and the soil temperatures on the possible in- crease or decrease of the Texas root rot disease. Accordingly, soil thermometers measuring 1, 3, 6, 12, 24, 36, and 48 inches were in- stalled at Substation No. 5, Temple, Texas. These thermometers (Fig. 15, b) were placed in the same field where most of the experi- ' mental work was carried out, and the readings taken three times a -day. Likewise, and in addition to outdoor and soil temperatures, the daily and the monthly precipitations were also taken into consideration. The recording of the soil temperatures began in 1917 and was con- tinued during 1918, 1919, 1920, 1921, 1922, and will be continued in the future as a soil temperature project. Since these data are to be published elsewhere, they will be referred to only indirectly. Because of limited space, we have compared and studied the soil temperatures and precipitation data of July, August, and September during the dry year of 1918, with similar months of the wet year of 1920. This was done for the purpose of tracing the relationship, if any, of soil tem- peratures to the prevalence or absence of Texas root rot. These studies are summarized in Table 11. Briefly stated, the temperatures for July, August, and September during a dry year such as 1918 at a soil depth of one to three inches were much hotter on the whole than the outdoor temperatures during the same dates in these three months. This is evidently due to the fact that the black waxy soils in Texas are capable of absorbing heat and holding it. On the other hand, as we go down deeper, the temperature decreases considerably, especially at the depths of 36 and 48 inches, but not enough to con- siderably cool the soil at these depths. In contrasting the data for a dry year in 1918 with those of a wet year in 1920 as shown in Table 11,‘ one will see that the outdoor and the soil temperatures are lower in a wet season than is the case in a dry summer. This is no doubt due to the cooling effect of the rain. Furthermore, it has been ob- served repeatedly that infection in most cases first begins at the tip end of the root system and gradually works up to the laterals, where it spreads to adjacent roots which happen to touch those of infected plants. This, then, would seem to indicate that moisture and a tem- perature varying from '70 to '78 degrees, as it occurs at a depth of 24 to 36 inches during a wet year, is most favorable for infection. On the other hand, during a dry year the temperatures for 36 and 48 inches during July to September are 5 to 15 degrees higher, and this prob- ably checks infection or retards the activity of the causal organism. This would perhaps seem to indicate that the deeper soiltemperatures, together with moisture, are important factors in determining the ‘ severity of the disease each season. This, of course, is to be verified and duplicated on indoor soil temperature boxes in the greenhouse where moisture and temperatures are under control. 35 TEXAS Room Row. ‘H555 »». mars: m5» 5:53 5m55:5 m5» 55»5:5 mo: »m5»5:.m5~mm 5:. 0:5. >:m:m» m5» $58858 @555 »0»w m5» »0M0 0:252. » 5% w 525m 0 525m 5 55am w» 5A5? w» 55am 5 55mm Wamflvfim- a. . 405m». Z555 zmx? g5? g5»? g5? gmx? BS5? g5»? g5? Z55? g5? 25x? g5? g5»? g5? g5»? g5? mwwiw 5:5 5:5 5:5 5:5 5:5 5:5 5:5 5:5 5:5 5:5 5:5 5:5 5:5 5:5 5:5 5:5 »0»w 0:5. . . . 2. . 0» 3 0< :w:m» . . . . . . . . . . . . . . 0» 5 0< << 0w ww 0» ww 0» w0 w0 w0 ww ww m» ww 5 5 5 5 5 5 5 . 5 5 5 5 5 5 5 5 5 0.0< 8w <0 »00 0w 5w 00 0w 0w 0w 0w 0w 00 ww ww ww wm »0m0 >:w:m» . . . . . . . . . . . <0 0w 9... Zo. 2.90 @309. 0.9. 9.3 0.09.0 0.. <09... . 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M00399... 00 . . . . . . . . . . 00.0 000.Q0 88.5.... .6929; 0000 . . . . . . . . . . . . . . . . . . . . .. 0 Q > Q0100 . . . . . . . . ..... 00000.9. 00. . . . . . . . . . .. Q.0 000.00 Q00 000.00 0000 . . . . . . . . . . . . . . . . . . . . .. 0 Q > Q0100ZI... . . . . .. 0300...... 00. . . . . . . . . . .. 00.0 000.00 000. . . . . . . . . . . . . . . . . . . . . .. 0 Q 0w Q0100. . . .. . . . . . . .. 0300.9. 00 . . . . . . . . . . .. 0.00 000.00 46 BULLETIN No. 307. Table 15. Effect of non-rotation on Texas root rot of cotton. Average Total yield Average yield Root Bot pounds per cent pounds Year Acre No. seed cotton root rot seed cotton Date counted Per cent per acre per acre 1916 C 33 . . . . . . . . . . . .. October 25 . . . . . . .. 28.5 516.79 1917 C 33 . . . . . . . . . . .. October 1 . . . . . . . .. 14.54 289.37 1918 C 33 . . . . . . . . . . .. September 25 . . . . .. 8.50 98.59 7 non- 7 non- 1919 C 33 . . . . . . . . . . . . October 20 . . . . . . . . 45.00 555.31 rotations rotations 1920 C 33 . . . . . . . . . . .. October 25 . . . . . . .. 37.50 612.50 19.77 451.40 1921 C 33 . . . . . . . . . . . . September 19 . . . . . . 3.00 700.00 1922 C 33 . . . . . . . . . . . . October 24 . . . . . . . . 1.40 387.30 1916 F 14 . . . . . . . . . . . .. October 25 . . . . . . .. 32.00 510.03 1917 F 14 . . . . . . . . . . . .. October 1 . . . . . . . .. 17.43 335.00 1918 F 14 . . . . . . . . . . . .. September 25 . . . . .. 5.25 117.18 7 non- 7 non- 1919 F 14 . . . . . . . . . . . . . October 20 . . . . . . . . 60.00 316.87 rotations rotations 1920 F 14 . . . . . . . . . . . . . October 25 . . . . . . . . 55.00 668.75 39.19 355.49 - 1921 F 14 . . . . . . . . . . . .. September 19 . . . . .. 78.00 175.00 1922 F 14 . . . . . . . . . . . . . October 24 . . . . . . . . 26.70 365.60 1919 G 1-20 . . . . . . . . . . October 20 . . . . . . .. 28.00 . . . . . . . . . . 4 non- 3 non 1920 G 1-20 . . . . . . . . . . . October 25 . . . . . . . . 96.00 760.70 rotations rotations 1921 G 1-20 . . . . . . . . . . September 19 . . . . . . 56.00 511.50 48.63 557.59 1922 G 1-—20 . . . . . . . . . . October 24 . . . . . . . . 14.55 400.57 1916 A 61-70 . . . . . . . . .. October 25 . . . . . . .. 15.00 1012.70 1917 A 61—70.......... Octoberl . . . . . . . .. 6.68 366.43 1918 A 61-70 . . . . . . . . .. September 20 . . . . .. 8.00 392.50 7 non- 7 non- 1919 A 61-70. . . . . . . . . . October 20 . . . . . . . . 28.00 451.83 rotations rotations 1920 A 61-70 . . . . . . . . . . October 25 . . . . . . . . 44.50 696.00 24.03 552.12 1921 A 61-70 . . . . . . . . . September 19 . . . . . . 58.33 482.33 1922 A 61-70 . . . . . . . . . October 24 . . . . . . . . 7.76 463.06 Texas farmers have, of course, practiced crop rotation with the hope of reducing or controlling the Texas root rot disease of cotton. No matter where tried, nor how persistent, crop rotation has not always given the results which were claimed for it. We do not intend to give the impression that we are condemning the idea of crop rotation. However, from our life history studies as seen on page 72, we are now able to explain why this practice has not in the majority of cases given the results which it was hoped it would give and where, in the light of our own studies, success may take the place of failure. Perhaps the only plausible explanation of this failure is the fact that wherever crop rotation was religiously practiced, one important factor was un- consciously overlooked, or neglected, namely, clean culture. We shall herein discuss on page 89 the fact that where clean culture is not practiced, a chance is given to certain susceptible perennial weeds to carry over the root rot fungus on the living roots during the winter months. It is this fact, which until now, has not been definitely known, that may explain the failure of crop rotation. We shall now refer to various types of crop rotation advocated or practiced which ' have not given the desired results and we shall point out the probable cause of the failure. We have stated that Heald (9) recommended a one-year rotation of corn and cotton. This rotation has actually been tried out by many farmers with varying results. In most cases, how- ever, where weeds are not thoroughly killed out, there is as much root rot after the corn as if that crop had not been grown. For this reason this system of rotation is generally condemned by many. Any- one who is familiar with the methods in vogue in Texas in producing a corn crop will realize that the farmer usually goes to the trouble TEXAS Roor Ror. 47 to prepare the land and keep the crop fairly clean as long as he can penetrate with his tools and work ‘it. However, as soon as the corn is made and the ears mature, the field is left to itself without further attention or cultivation. The result is that nearly all of the corn fields in Texas become a veritable weed garden immediately after the last cultivation and beginning with the ripening of the corn crop. The corn is thus left in the field sometimes until late in the fall, when it is harvested and nothing further done to the field until the follow- ing spring. If there is any doubt about this, let anyone go into the average corn field during the summer, fall, or Winter months and see if he cannot find there one or more types of susceptible weeds, espe- cially the cocklebur, Xanthium spp., in various stages of dying from the Texas root rot and also numerous instances of living roots of perennial weeds, especially I pomoea trichocarpa, which carries over the causal organism during the winter months. To support the above contention, we shall cite a specific illustration. On October 24, 1922, an average corn field was picked out in Bell County, Texas. Counts were made of the number of cocklebur plants in the field which were alive and those which died from Texas root rot. The results of this count are shown in Table 16, which is self-explan- atory. Table 16. Cockleburs in a corn field. Row Row Condition of plants No. 1 No. 2 Average Per cent l I ’ l Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 77 93.0 100.0 Died from Texas root rot . . . . . . . . . . . . . . . . . . . 49 14 31 .5 33.8 Alive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 63 61 .5 66.2 Cases of unsuccessful three-year rotations may be mentioned-pats or wheat, corn, and cotton. Here again, the failure may be traced to a lack of clean culture in the rotation system. For instance, as soon as the oats or wheat is harvested, the stubble is generally plowed up and the land is not planted to a crop until the following year, when it is planted to corn. This fallow stubble land, as is frequently the case, becomes overrun by a number of susceptible weeds which maintain the Texas root rot organism during the summer, fall, and winter months. This is especially true of I pomoea trichocarpa, the roots of which remain alive in the soil and sprout with the least moisture. Further- more, the corn crop the second year, likewise, furnishes sufficient weed flora to carry the Texas root rot to the cotton the third year. Believing that a three-year rotation is not always effective in con- trolling root rot, farmers in many cases have practiced a four-year rotation with the hope of reducing the ravages from the Texas root rot disease, but with no better results. In a four-year rotation such as: (a) cowpeas; (b) corn; (c) wheat, and (d) cotton, the- causes of failure at control may be explained as for the other rotations. To begin with, cowpeas planted during the first year are highly susceptible to Texas root rot. After the cowpeas are harvested, and the vines 48 BULLETIN No. 307. turned under, there are usually enough susceptible weeds left over to perpetuate the root rot fungus during the winter months. Likewise, during the second year the weeds which are permitted to thrive after the last cultivation of the corn and those found the third year on the wheat stubble are suflicient to maintain the disease for the cotton crop the fourth year of the rotation. There may be any number of crop rotations practiced, but whenever the question of clean culture is overlooked, and by this we mean a clean culture not only during the period in which the crop is grown, but also clean culture of the fallow land during the fall and winter months, the system of rotation practiced may be a failure or give only partial results under root rot conditions. Effect 0f Lime 0r Sulphur on Texas Root Rot. Claims are fre- quently made by farmers and fertilizer concerns that lime or sulphur when used alone or in combination act as a check to the disease. In order to determine the effect of the two elements, a cooperative experi- ment was undertaken uiith the Division of Agronomy, this Division testing its effect on the growth and production of seed cotton per acre and the Division of Plant Pathology and Physiology studying the effect of these applications on the possible control of the Texas root rot disease. The object in this experiment was to determine the effect, if any, of soil acidity or alkalinity on the Texas root rot and as brought about by the applied lime or sulphur. The amounts used and the results obtained during the last three years are indicated in Tables 1'7, 18, and 19. It should be added that the years 1920 and 1921 were both favorable for the Texas root rot because of the prevalent showers during June and July. On the other hand, during 1922 there was a scarcity of rainfall during these two months, resulting in little root rot. Table 17. Efiect of sulphur onITexas root rot. _Total yield _ Per cent in pounds of Year Acre No. Plat Amount 1n pounds per acre root rot seed cotton per acre per acre 1 Check . . . . . . . . . . . . . . . . . . . . . . . 20 496.0 1920 At Cater’s farm. . 2 Sulphur 100 . . . . . . . . . . . . . . . . . 28 608.0 3 Sulphur 100 . . . . . . . . . . . . . . . . . 24 632.0 4 Sulphur 600 . . . . . . . . . . . . . . . . . 18 776.5 1 Check . . . . . . . . . . . . . . . . . . . . . . . 81 .6 720.0 2 Sulphur 1 .000 . . . . . . . . . . . . . . . 63.4 1380.5 3 Sulphur 500, acid phosphate 400 74.4 960.2 4 Sulphur 25 . . . . . . . . . . . . . . . . . . 83.3 600.0 1920 G 1-20 . . . . . . . .. 5 Check . . . . . . . . . . . . . . . . . . . . . .. 96.0 760.7 6 Sulphur 50, acid phosphate 400. 72.4 900.0 7 Acid phosphate 400 . . . . . . . . . . . 85.4 680.2 8 Sulphur 50 . . . . . . . . . . . . . . . . . . 82.4 940.7 9 Check . . . . . . . . . . . . . . . . . . . . . . . 92.8‘ 684.2 *Yield data furnished by the Division of Agronom , Texas Agricultural Experiment Station. gieellsgggtllzgyiiggzl?) E. B., and Leidlgh, A. H. Sulp ur as a fertilizer for cotton. Soil Science TEXAS R001‘ R01‘. Table 18. Effect of lime or sulphur on Texas root rot.* 49 i Total yield _ Per cent 1n pounds of Year Acre No. Plat Amount 1n pounds per acre root rot seed cotton No. per acre per acre 1 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 792 2 Lime 500 . . . . . . . . . . . . . . . . . . . . . . . . . . 26 660 3 Sulphur 500 . . . . . . . . . . . . . . . . . . . . . . . 35 550 4 Lime 500. sulphur 500 . . . . . . . . . . . . . . 53 418 5 Lime 2,500 . . . . . . . . . . . . . . . . . . . . . . . . 61 396 6 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 374 7 Sulphur 2,500 . . . . . . . . . . . . . . . . . . . . . . 98 27.5 1921 G 1-20 8 Lime 2,500, sulphur 2,500 . . . . . . . . . . . 69 24.05 9 Lime 5,000 . . . . . . . . . . . . . . . . . . . . . . . . 7O 108.62 10 Sulphur 5,000 . . . . . . . . . . . . . . . . . . . . . . 89 110 11 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . s2 286 12 LIIIIB . ,00O, sulphur 5,000 . . . . . . . . . . . 73 275 13 Lime 10,000, sulphur110,000 . . . . . . . . . 45 396 14 Sulphur 10,000 . . . . . . . . . . . . . . . . . . . . . 28 396 15 Lime 10.00 . . . . . . . . . . . . . . . . . . . . . . . . 26 484 16 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 594 1 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 558 2 Lime 500 . . . . . . . . . . . . . . . . . . . . . . . . . . 24 864 3 Sulphur 500 . . . . . . . . . . . . . . . . . . . . . . . 17 800 4 Lime 500, sulphur 500 . . . . . . . . . . . . . . 16 880 5 Lime 2,500 . . . . . . . . . . . . . . . . . . . . . . . . 13 887. 5 6 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 880 7 Sulphur 2,500 . . . . . . . . . . . . . . . . . . . . . . 12 704 1921 E 1-10 8 Lime 2,500, sulphur 2,500. . .. . . .. . . . . 7 770 9 Lime 5,000 . . . . . . . . . . . . . . . . . . . . . . . . 5 902 10 Sulphur 5,000 . . . . . . . . . . . . . . . . . . . . . . 4 704 11 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 748 12 Lime 5,000, sulphur 5,000 . . . . . . . . . . . 16 671 13 Lime 10,000 . . . . . . . . . . . . . . . . . . . . . . . 8 814 14 Sulphur 10,000. . . . .' . . . . . . . . . . . . . . . . 12 638 15 Lime 10,000, sulphur 10,000 . . . . . . . . . 9 792 16 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682 *Yie1d data furnishedlby Division of Agronomy, Texas Agri cultural Experiment Station. 50 BULLETIN No. 307. Table 19.: Effect of lime or sulphur on Texas root rot.* l F“ Total yield r _ Per cent in pounds of Year Acre No. Plat Amount in pounds per acre root rot seed cotton No. per acre per acre 1 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 539.0 2 Lime omitted . . . . . . . . . . . . . . . . . . . . . . 9. 1 506.0 3 Sulphur 500 . . . . . . . . . . . . . . . . . . . . . . . 16.3 453.6 4 Lime omitted. sulphur 500 . . . . . . . . . . . 32.6 410.9 5 Lime omitted . . . . . . . . . . . . . . . . . . . . . . 19.8 401.2 6 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 346.2 g 7 Sulphur 2.500 . . . . . . . . . . . . . . . . . . . . . . 21 .4 269.2 1922 G_ 1-20 8 Lime omitted, sulphur 2,500 . . . . . . . . . 16. 1 273.2 9 Lime omitted . . . . . . . . . . . . . . . . . . . . . . 23.9 262.2 10 Sulphur 5,000 . . . . . . . . . . . . . . . . . . . . . . 22.4 266.6 11 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.9 326.9 12 Lime omitted, sulphur 5,000 . . . . . . . . . 20.9 295.6 13 Lime omitted . . . . . . . . . . . . . . . . . . . . . . 4.6 380.6 14 Sulphur 10,000 . . . . . . . . . . . . . . . . . . . . . 0.9 345.4 15 Lime omitted, sulphur 10,000 . . . . . . . . 1.4 336.6 16 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 0.9 390.2 1 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.6 622.82 2 Sulphur 50 . . . . . . . . . . . . . . . . . . . . . . . . 27.5 589.16 3 Sulphur 100 . . . . . . . . . . . . . . . . . . . . . . . 20.2 655.16 4 Sulphur 200 . . . . . . . . . . . . . . . . . . . . . . . 19.7 634.04 5 Sulphur 300 . . . . . . . . . . . . . . . . . . . . . . . . 11.5 700.70 6 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 683.32 7 Sulphur 400 . . . . . . . . . . . . . . . . . . . . . .. 4.0 619.08 1922 E 1-10 8 Sulphur 500 . . . . . . . . . . . . . . . . . . . . . . . 3.0 689.04 9 Sulphur 1,000 . . . . . . . . . . . . . . . . . . . . . . 1 . 1 630.3 10 Sulphur 1,500 . . . . . . . . . . . . . . . . . . . . . . 7.3 619.08 11 Chec . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2. 1 642.40 12 Sulphur 2,000 . . . . . . . . . . . . . . . . . . . . . . 2.3 617.32 13 Sulphur 2,500 . . . . . . . . . . . . . . . . . . . . . . 2.9 513.70 14 Sulphur 3,000 . . . . . . . . . . . . . . . . . . . . . . 4.7 457.16 15 Sulphur 4,000 . . . . . . . . . . . . . . . . . . . . . . 1 .3 423.06 16 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 490.82 1 Check . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14.3 615.88 2 Sulphur 50 . . . . . . . . . . . . . . . . . . . . . . .. 15.3 20.2 3 Sulphur 100 . . . . . . . . . . . . . . . . . . . . . . . 10.8 526.43 4 Sulphur 200 . . . . . . . . . . . . . . . . . . . . . . . 28.3 442.11 5 Sulphur 300, . . . . . . . . . . . . . . . . . . . . .. 29.3 479.51 6 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.0 436.25 7 Sulphur 400 . . . . . . . . . . . . . . . . . . . . . . . 18.8 408.39 1922 C D E ~ 8 Sulphur 500 . . . . . . . . . . . . . . . . . . . . . . . 43.7 291.81 01-010 9 Sulphur 1,000 . . . . . . . . . . . . . . . . . . . . . . 38.8 278.75 10 Sulphur 1,500 . . . . . . . . . . . . . . . . . . . . .. 12.6 291.81 11 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 289.61 12 Sulphur 2,000 . . . . . . . . . . . . . . . . . . . . . . 4.1 397.39 13 Sulphur 2,500 . . . . . . . . . . . . . . . . . . . . .. 2.8 194.29 14 Sulphur 3,000 . . . . . . . . . . . . . . . . . . . . . . -9.0 173.76 15 Sulphur 4,000 . . . . . . . . . . . . . . . . . . . . . . 3.6 261.75 16 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 252 .95 *Yield data furnished by Division of Agronomy, Texas Agricultural Experiment Station. In carefully studying Tables 1'7 to 19 one sees that neither lime nor sulphur has controlled 0r reduced the Texas root rot in cotton. It should be remembered, however, that these tests are not as yet final, as there is a possibility that the amount of sulphur used was not as yet sufficient to overcome the soil alkalinity and render it suffi- ciently acid to control the disease. In fact, acidity tests of the treated plats carried out by Mr. Reynolds of the Division of Agronomy bear this out. This means that these experiments must be carried on for sev- eral more years before We can adopt or discard the use of sulphur in the control of the Texas root rot. As to the lime, its use in this con- nection has been discontinued during 1922. Lime has apparently no efiect in increasing or diminishing the disease. TEXAS R001" R01‘. 51 EFFECT OF FERTILIZER AND INOOULATED SULPHUR ON TEXAS ROOT- ROT. From time to time, claims were made that the application of cer- tain fertilizers to infected land will materially help t0 reduce the rav- ages of the root rot disease. Pammel (15) states a case near Brenham, Texas, in which two infected acres were heavily top-dressed with ma- nure with the result that the percentage of the dead cotton decreased decidedly. He further cites a case Where the use of cotton seed meal resulted not only in the production of a bale of cotton per acre, but it materially helped to reduce the Texas root rot disease. Likewise, he tried out various fertilizers or fungicides as agents in controlling Texas root rot, which were as follows: kainit, chloride of potash, sul- phate of magnesium, cotton seed meal, chloride of lime, sulphate of iron, alum, copper sulphate, sodium chloride, white arsenic, ve-rdigris, lac-sulphur, carbolic acid, lime, salt and lime, lime and copper sul- phate (dry), lime and copper sulphate (solution), sodium chloride and kainit. Of all these, not a single one tried Was able to check the root rot, with the exception perhaps of the chloride of lime. How- ever, where this was used, very little cotton was produced. Curtis (3), too, recommends the application of salt and coal oil (kerosene) in con- trolling Texas root rot in cotton or alfalfa. As to the amount of salt to use, he advises that enough should be applied to the young plants to make the surface of the treated soil thoroughly white in appearance. As for the coal oil, he recommends that a sufiicient amount be used to thoroughly drench the treated land. While we have not tried out the use of either salt or coal oil, it is very doubtful if they will con- trol root rot when used in small doses, and when used in excess, plant growth may be prohibited altogether. Table 20. Effect of fertilizer on Texas root rot.* . _'I‘otal yield _ Per cent 1n pounds of Year Acre No. Plat Amount 1n pounds per acre root rot seed cotton No. per acre per acre 1 Nitrate of soda 160 . . . . . . . . . . . . . . . . . 78 145 . 2 Nitrate of soda 80 . . . . . . . . . . . . . . . . . 67 80 1921 3 Acid phosphate 400 . . . . . . . . . . . . . . . . . 33 490 4 Acld phosphate 200 . . . . . . . . . . . . . . . . . 29 440 5 Lime 10.000, manure 20.000 . . . . . . . . . 22 540 6 Manure 20,000 . . . . . . . . . . . . . . . . . . . . . 34 490 1 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 302.77 2 Guano 300 . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 256.85 3 Nitrate of soda 100 . . . . . . . . . . . . . . . . . 2.7 235.67 4 Sulphur 300 . . . . . . . . . . . . . . . . . . . . . . . 1.9 168.30 1922 C 35-40 5 Sulphur, Toyah Valley, 400 . . . . . . . . . . 3.1 160.30 6 Brown Ore 20 A. P . . . . . . . . . . . . . . .. 4.5 161 .42 7 Brown Ore 200 A. P . . . . . . . . . . . . . . . . 4.8 160.05 8 Manure 14,000 . . . . . . . . . . . . . . . . . . . . . 6.4 203.50 9 Inoculated agricultural sulphur 400. . . 12.8 142.17 10 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10.6 166. 10 *Yield data furnished by the Division of Agronomy, Texas Agricultural Experiment Station. . Fertilizer experiments during the last two years carried on by the writers in cooperation with the Division of Agronomy of this Station have not yielded anything definite. In referring to Table 20, one is 52 BULLETIN N0. 307. convinced of the necessity of carrying on these experiments for a number of years before reaching definite conclusions. The data ob- tained so far are conflicting and inconclusive. Efiect of Soil Disinfectant on Texas Root Rot. Mention has already been made of the work of Pammel (15) in trying out various chemicals and their effect as soil sterilizers with but little or no results. The writers realize that no amount of soil treatment by chemicals would be possible or practical on a large scale. However, when we consider the great damage occasioned by Texas root rot disease to various out- door ornamentals, it becomes evident that some standard soil disin- fectant may be practical on a small scale. Since we had no steam facilities at Substation No. 5, it was decided to try out the effect of formaldehyde, chlorophol, and Seed-O-San. The formaldehyde was used during 1921 and 1922 at the rate of one pint in twenty gallons of water and the solution was applied at the rate of two gallons per square foot. The soil treated was protected by a wooden frame, and ten days after treatment okra was planted, since this host is extremely sus- ceptible to the root rot disease. A check plat which was untreated was also sown to okra next to and adjoining the formaldehyde-treated plat. The chlorophol and the Seed-O-San were used at the‘ rate of one pound in twenty gallons of water, and tried during 1922 only. From Table 21, it is seen that during 1921, the formaldehyde appar- ently reduced considerably the percentage of the disease. However, it should not be taken as conclusive since this only represented one year’s trials. Nevertheless, these results are interesting in the sense that the treated plat actually showed a decided decrease in the disease com- pared to the check. This work will be duplicated for several more years and tried on various crops with root systems which penetrate more or less deeply into the soil. On the other hand, the treatments with the chlorophol and Seed-O-San during 1922 did not show any- thing because there was no root rot on the treated and check plats. But it was evident that the proportions of one pound in twenty gal- lons was strong, as it stunted the growth of the okra and reduced the yield in pods. _ _ Table 21. Effect of soil disinfectants on Texas root rot.* Per cent. Yield in Plat _ _ root rot pounds Year No Kind of soil disinfectant used ppr plat, of okra ov. 15 per plat 1921 1 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 . . . . . . . . . . . . 2 Formaldehyde . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 . . . . . . . . . . . . 1 Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 0 1 .75 1922 2 Chlorophol . . . . . . . . . . . . . . . . . . . . . . . . . ._ . . . . . . . . 0 6.00 3 Seed-O-San . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 8.50 4 Formaldehyde . . . . . . . . . . . . . . . . . . . . . . . . .' . . . . . . . 0 12.50 *Yield data furnished by the Division of Agronomy, Texas Agricultural Experiment Station, C»! 03 TEXAS Roor Ror. IS A TEXAS ROOT BOT SPOT PERSISTENT FOR A NUMBER OF YEARS. Farmers frequently claim that as far as cotton is concerned, a root rot spot one year does not necessarily mean the reappearance of the same spot the following year. Duggar (4) states, “In a field grown two or more years to cotton, one notices the disappearance of some of the small spots of the previous year.” Scofield (19), in his work on dead spots of cotton in Texas, likewise found that a root rot spot one year does not necessarily mean a root rot spot another year if the same susceptible host is grown on that land. The writers have studied this question for a period of five years with the result that we can safely corroborate the statements of the workers mentioned above. In gen- eral, it is safe to state that a root rot spot one year does not necessarily mean a root rot spot another year (compare Fig. 6, a and b), if a susceptible host is grown again on that same land the following year. However, it must be further added that the reason‘ for this is un- doubtedly the fact that the disease is able to kill out all susceptible hosts grown in any one spot during any one year. If, for instance, in any given cotton root rot spot, all the cotton is killed out as is usually the case, and if in addition all other annual and perennial susceptible weeds are also killed out, leaving no winter carriers, then the same spot will certainly not reappear the following year, no matter what favorable weather conditions may prevail. On the other hand, as it sometimes happens, some of the cotton plants or susceptible hosts are not all killed out in a spot; in which case there will be winter car- riers, and a root rot spot one year will reappear again the following year, given a favorable climatic condition for the disease. From this it becomes more evident that the causal fungus does not apparently live over in the soil, because if it did, it would maintain itself indefi- nitely there. Furthermore, a root rot spot would last as long as a susceptible crop was grown there. CAUSE OF THE TEXAS ROOT ROT DISEASE. Various Claims. Practically every cotton grower has at one time or another entertained certain ideas of his own regarding the cause of the Texas root rot disease. Even today, there are quite a few growers who believe that the trouble is caused by alkali in the soil. As seen in Table 22, soil analyses of various root rot spots do not show that there is enough alkali in those spots to be responsible for the dying of the cotton grown there. From Table r22 it is, therefore, very evident that the alkali theory is untenable. The work of Stewart (24) seems to indicate that cotton will stand a considerable amount of alkali and will even grow when the water table is within a short dis- tance of the surface of the land. The chief ill effect of alkali on cotton is that it causes the seed to germinate poorly. However, those seeds which do germinate grow fairly well and seem to produce normal plants and normal yields. 54 BULLETIN N0. 307. ' ||'|||||| ' | || I . I | ' I | a I I I Cowou Rom‘ R01‘ SPQTS ||l||| - , E __ ""' I I I A _ H ..|,,| ||||| I. ll I . I I l9\9 I. M . I I i . I I ' corrou R00’! R0": spars l9 2.0 FIGURE 6. a and b. Comparing a root rot spot during 1919 and 1920, both of which years were favorable for the disease. The black lines represent dead cotton plants in the rows. TEXAS R001‘ RoT. ' 55 Table 22. Chemical analyses of soil from root rot spots.* Active _ _ _ _ Percent phos- Act.1ve Acid Soluble Sample No. Origin of spots Nltro- phoric potash con- salts a gen acid parts_ per sumed parts per parts per million per cent. IIllll10I1 million 2 Okra dying from root rot. . . . 0 153 21 3 375.0 100 0 107 Subsoil to No. 2 Subsoil to No. 2 . . . . . . . . . . . . 0 143 16 9 287 5 100.0 82 Healthy okra plant . . . . . . . .. 0 152 17 5 295 0 100 0 61 Subsoil to No. 3 Subsoil to No.3 . . . . . . . . . . . . 0 128 9 4 88 7 100 0 81 4 Apple tree dying from root rot . . . . . . . . . . . . . . . . . . . .. 0 156 22 5 376 9 100 0 70 Subsoil to No. 4 Subsoil to No. 4 . . . . . . . . . . . . O 157 16 9 276 2 100 0 70 - 5 Healthy apple tree. . . . . . . . . . 0 137 17 7 273 1 100 0 39 Subsoil to No. 5 Subsoil to N0. 5 . . . . . . . . . . . . 0 129 12 5 278 7 100 0 67 Healthy cotton plant . . . . . .. 0 140 26 3 268 1 100 0 78 Subsoil to No. 6 Subsoil to No. . . . . . . . . . . . . 0 143 34 4 138 7 99 7 50 7 Cotton plant dying from root rot . . . . . . . . . . . . . . . . . . . .. 0 134 14 8 225 0 99 7 38 Subsoil to No. 7 Subsoil to No. 7 . . . . . . . . . . . . 0 175 16.9 118 7 100 0 20 9 Dead grape killed by root rot._ . . . . . . . . . . . . . . . . . . .. 0 112 6.8 159 3 100 0 31 Subsoil to No. 9 Subsoil to No. 9 . . . . . . . . . . . . 0 110 5.0 63 7 100 0 45 10 Healthy grape . . . . . . . . . . . .. 0 113 5.6 174 3 100 0 34 Subsoil to No. 10 . . . . . . . . .. Subsoil to No. 10 . . . . . . . . . .. 0 100 5.0 48.7 100 0 48 *Th_ese analyses were made by Dr. G. S. Fraps, Chief Chemist of the Texas Agricultural Experiment Station. Pammel (15) refers to claims by growers that the Texas root rot disease is brought about by soil acidity—probably sulphuric acid in the heavy black lands. This acid is believed to be formed by the de- composition of iron sulphate present in the soil. Through the in- fiuence of sunlight and air, the iron sulphate is brought up to the surface by the cultivator or the plow. Through the action of air and sunlight, it is finally transformed into free sulphuric acid, which kills the plants. Such acid spots, it is claimed, grow wider and wider as the iron sulphate increases. Experiments by Pammel (15), however, show that cotton may tolerate as much as 2%; per cent. solution of iron sulphate Without dying. It might be interesting to further add that some growers believe that when the land is plowed Wet the plants in that land will die from the root rot disease. Others claim that Texas root rot is brought about when cultivation of the cotton is suddenly stopped for two or three weeks and this is followed by heavy rains, and the land is worked when still wet. Others still believe that the rains during June and July are directly responsible for the dying of the cotton. For this reason, it is not uncommon to find people claim~ ing that an overflow in heavy, bottom lands will cause the Texas root rot disease. FUNGOUS NATURE 0F THE DISEASE. Pammel (15) was the first to have suspected and to believe that Phymatotrtchum omnivorum (Ozonium omnivorum) was the cause of the Texas root rot disease of cotton, as he states that “It has been amply proved that Ozonium (Phymatotrichum) is the cause of root rot. (Experimental proof not stated.) It is universally admitted that where the disease is once established, cotton will die year in and year out unless checked. If sweet potatoes, grapes, mulberries, apples, 56 BULLETIX No. 307. \ FIGURE 7. a. Showing method of isolating Phymatorrichuwz omnivorumr by dropping in a sur- face sterilized section of freshly infected cotton root into a sterile tube slant of agar agar. b. Same as a, two weeks later, showing growth of the causal organism. c. Test tube cultture of P. omnivorum on sterilized mulberry stem. d. Same as c, two weeks older, showing sclerotia formation at the mouth end. e. Showing strand forma- tion on glass wall of a culture of P. omnivorum. f. P. omnit-orum grown on Tsteril- ized slices of Irish potato. g. On sweet potato slices. h. On potato starch. i. On navy beans. j. On rice. k. On crushed cotton seed (e to 1c, cultures grown in 500 c.c. Ehrlmayer flasks). l m“ ~ .. “mwnzhk. i TEXAS Roor Rorr. 57 chinaberry trees, cowpeas, andother susceptible crops will follow each other, they will all die in the same way and from the same cause, namely, Ozonium.” We shall soon show that Pammel Was correct in his belief of the fungous nature of Texas root rot. Isolation of Phymatotrichum Omnivorum. It has already been men- tioned that Pammel (15) strongly suspected that Ozonium (Phyma- totrichum omnivorum) was the cause of the Texas root rot disease. He attempted to grow the organism on artificial media, but without suc- cess, as he would nearly always wind up with contamination of a varied mycological flora, consisting of such fungi as Tricothecium, Verticil- lium, Cladosporium, species of Mucor, and putrefying bacteria, but no Ozonium. Atkinson in writing to Curtis (3) states, “I am trying to l obtain a pure culture of Ozonium, but I find it much more difficult to transplant with success.” However, be it said to the credit of Atkin- son (1) that he was the first to have succeeded in growing Phyma- totricltum omn/ivorum in pure culture by adopting the following rather crude method. He first secured fresh material of infected cotton stalks from Texas, and then rinsed'the roots of these plants in distilled water. He then cut the roots into small pieces and placed them on sterilized filter paper which was lying on sterile sand in a moist chamber. In a few days, the Ozonium (Phymatotrichum). strands grew out from the infected tissue over the paper on the sterilized slides. He then took bits of sterilized cotton roots and placed them in contact with the advancing hyphae. When the hyphae started to grow on the ster- ilized bits of cotton roots they were transferred to various media. That Atkinson (1) grew the fungus on culture media there seems no doubt. However, the senior writer in duplicating this method found it very tedious and not always reliable, as secondary infection would readily get in in spite of the greatest precaution. Not only did Atkinson have difficulty in isolating the Ozonium (Phymatotrichum) fungus in pure culture, but Duggar (4) states that “The organismlis none too readily isolated.” Shear (20) and Shear and Miles (21 and 22) do not state whether or not they have ever grown Ozonium in pure culture. However, Miles has written to one of us stating that he had no trouble whatsoever in growing Phyma- totrichum omnrivorum in pure culture. The first attemptby the senior writer met with considerable disap- pointment. In-fact, during 1917 and 1918, it is doubtful if we ever had the organism growing pure on media. However, and after dis- carding numerous methods, we adopted Atkinson’s method of isolation, but modified it as follows: Freshly infected cotton plants were secured from Temple, Texas, and immediately shipped to College Station. These plants after arriving at destination, were carefully Washed in running tap water to remove every trace of soil particles, and the tops cut off and discarded. These roots were then cut up into small pieces and everything discarded except bits one-half inch‘ long, which were taken from the area immediately adjoining the healthy tissue, and con- sisting of partly healthy and partly diseased tissue. These pieces were then disinfected for one-half minute in an ordinary test tube in a solu- 58 BULLETIN No. 307. tion made up of equal parts of 1-1000 mercuric chloride and 50 per cent. alcohol. The disinfectant was thendrawn off and the pieces of root tissue Washed four times in sterilized water to remove all traces of the disinfectant. After this each piece of the root tissue thus treated was inserted in a slanted tube of solidified sterilized agar agar media. (Fig. '7, a.) After three to five days the Ozonium would grow out on the surface from the tissue within (Fig. '7, b) ; then on the agar slant. It was necessary, each time, to make a large series of cultures before the organism was finally obtained. During each attempt 100 to 300 tube cultures were thus made, and out of these, on an average, only 5 per cent. gave a growth of Phymatotrichum omnivorum. From these tubes the fungus was then transferred to other tubes of sterilized agar agar media or to various vegetable media '(Fig. '7, c to k) and in this way and by repeated transfers, accompanied by microscopical examina- tions, it was made certain that the Phymatotrichum omnivorum fungus was isolated pure. Once a pure culture of Phymatotrichum omnivorum is obtained, it may be transferred to practically all sorts of sterile media consisting of agar agar or of cooked vegetables, etc. We have already mentioned the difficulty met with, especially by beginners, when attempts are made to isolate Phymatotrichum omniv- orum in pure culture. In this connection, it should be added that the writers were not able to isolate the causal organism from any suscep- tible roots which had been dead more than two or three weeks. ARTIFICIAL INOOULATION. Pammel (15) not only desired to isolate the causal organism, but he also tried some artificial inoculations with the hope of proving that the Ozonium (Phymatotrichum omnivorum) was the cause of the Texas root rot disease. Pammel (15) noticed that plants that died from the Texas root rot disease were always superficially covered by threads of the causal fungus. However, since he found it diflicult to isolate the organism, he, of course, did not prove its parasitism. Duggar (4) states, “It seems that no successful inoculation experiments have been reported with this fungus (Phymatotrichum omnivorum). During two seasons, I have attempted to transfer the disease to potted cotton plants in the greenhouse. Diseased roots of cotton and alfalfa show- ing an abundance of the fungus were placed beneath the soil in contact with the healthy roots of half-grown plants. In every case, the fungus failed to spread and after a few months seemed to be dead.” Duggar (5), in a further attempt to carry on artificial inoculations, writes, “It should be said that no inoculations carried out in the greenhouse up to the present have given positive results. As a source of infection, I have employed (a) diseased cotton roots, fresh from the field (show- ing the Ozonium in abundance) ; (b) fresh conidia of Phymatotrichum omnivorum, and (c) cultures from diseased roots.” It thus seems that although various workers have considered Phymatotrichum omniv- orum to be the cause of the Texas root rot disease, yet this was only merely through circumstantial evidence, as proof was still lacking. TEXAS Roor R01‘. 59 The circumstantial evidence of the fungous nature of Texas root rot may be summarized as follows: (a) Phymatotrichum omnivorum from its field behavior does not seem t0 be a wound parasite, but seems to be able to penetrate its host either by breaking through the cell wall of the epidermis or through some lenticle. (b) From our own studies we believe that Phymatotr-ichum omnivorum is unable to subsist on dead plants or on organic matter in the soil. At least, it cannot do so through its fungus threads only. On the other hand, it lives and thrives continuously on live susceptible roots which it infects during the summer months, and on living but dormant susceptible roots dur- ing the Winter months, indicating its probable parasitic nature. (c) Phymatotrichum omnivorum always seems to start from a given center of infection and progresses in a definite way killing healthy plants as the fungus spreads and reaches out to the roots of adjoining healthy plants. (d) When a susceptible host is killed by the so-called Texas root rot disease, the typical fungus threads of Phymatotrichum omniv- orum- are always present and can be seen evenwith the naked eye on the affected roots. (e) Affected plants die progressively, one by one, and in the same ratio as the mycelium of Phymatotrichum omnivorum is able to reach out from the infected plant which overlaps and touches the roots of another adjoining healthy, susceptible host. (f) All sus- ceptible plants when infected exhibit symptoms common to all. (g) Phymatotrichum omnivorum seems to kill its host by means of an enzyme. This is evidenced by the fact that there is always a dark area preceding the area in which the Phymatotrichum fungus is found. This dark area as far as has been tested, seems to be sterile, that is, free from fungus hyphae. (h) Young plants may die without affect- ing adjacent plants while older plants with a better developed root system generally die progressively within a few days from the out- break of the infection of the first plant due no doubt to an overlapping of the root system. 6O BULLETIN No. 307. FIGURE 8. a and d. Wilting of cotton plants artificially inoculated with Phymatotriciz-izm omnivorum. b and e. Later stages of a and d, showing bare stalks, the leaves of which dropped off as a result of the successful inoculation. c. Check, uninoculated and healthy. f. Pure culture of Phymatotrichuan omnivomm on sterilized soil in 1000 c.c. Ehrlmayer flasks, in which the conidia spores were obtained. g. Photo of f showing areas where conidia spores are formed. This picture was taken by remov- ing the cotton plug 0f f, and by focusing the camera into the flask. ‘July 15, 1919 College Station Placed freshly-infected beet. roots TEXAS Roor RoT. 61 Table 23. Unsuccessful inoculation experiments. No. of Date Place of _ plants Inoculated Inoculation Method of inoculation inoculated Results Aug. 4, 1918 Substation No. 5 Placed roots of freshly-infected cotton plants near roots healthy scratched plants and _ _ _ covered with soil. . . . ._ . . . . . . . . 15 No infection Sept. 7, 1918 Substation No. 5 Placed roots of freshly-infected cotton plants near roots healthy scratched plants and _ _ covered with soil . . . . . . . . . . . . . 32 No infection July 7 , 1919 Substation No. 5 Placed freshly-infected beet roots near healt y scratched cotton roots and moistened with sterile _ water . . . . . . . . . . . . . . . . . . . . . . . 17 No infection July 15, 1919 College Station Placed freshl -infected cotton Greenhouse roots near ealthy scratched cotton roots growing in galva- nized tank in steam sterilized soil and moistened with steri- _ _ lized water . . . . . . . . . . . . . . . . . . 48 No infection July 15, 1919 College Station _ _ Greenhouse Checks . . . . . . . . . . . . . . . . . . . . . . . . 10 checks No infection Greenhouse near cotton roots growing in galvanized tank in steam steri- lized and moistened with steri- _ lized water . . . . . . . . . . . . . . . . . . 52 No infection Sept. 5, 1920 College Station Placed bits of mycelium from a Greenhouse tube (pure culture) Phymato- trichum omnivorum near healthy scratched cotton roots_ growing in galvanized tanks in_steam sterilized soil and moistened _ _ with sterilized water . . . . . . . .. 43 No infection Sept 5, 1920 College Station Greenhouse Check . . . . . . . . . . . . . . . . . . . . . . . . . 1O checks No infection Unsuccessful Inoculations. In 1918, 1919, and 1920, the senior writer attempted to carry out inoculation experiments on cotton grown both in the field at Temple, Texas, and in the greenhouse, but with negative results (see Table 23). Soil collected directly from spots where cotton died in the field was shipped from Temple, Texas, to College Station and placed in six galvanized tanks of a capacity each of 4x3x212~ feet. Cotton was then planted in all the six tanks during 1918, 1919, and 1920. The methods of inoculation and the negative restslts obtained are indicated in Table 23, which is self-explanatory. Successful Inoculations. Our new method of inoculation was as follows: Transfers oi pure cultures of Phymatotrichum omnivorum were made on pieces of sterilized stems of either mulberry or cotton roots in tubes. After ten days from the time of the original transfers, the fungus grew very luxuriantly on these vegetable plugs in the tubes (Fig. 7, c and d). At the same time cotton plants six weeks old which were more or less Woody, apparently healthy, and fairly well developed were carefully washed in running tap water, without bruis- iiig any parts of the plant; then the roots were quickly dipped into a solution consisting of equal parts of 50 per cent. alcohol and 1-1000 mercuric chloride, and again dipped in sterilized water to remove all traces of the disinfectant. Each of these plants was then planted, singly in bottles (Fig. 8, a and c) which contained steam-sterilized soil. The bottles (Fig. 8, c) were closed with a cork, the center of which was burned out by a hot iron rod to permit the ready introduc- 62 BULLETIN N0. 307. tion of the root of the cotton plant above mentioned (Fig. 9, a). Eight bottles were thus planted each with one individual cotton plant and permitted to remain for four weeks until we were fully satisfied that the transplanted cotton plants were fully alive and had actually developed new roots and leaflets, the older foliage in most cases having dropped off through the shock of transplanting. On December 30, 1921, actively-growing pure cultures of Phymatotrichum omnivorum on either sterilized mulberry stems or cotton roots were used for inocu- lation purposes (Fig. '7, c and d); One tube was used to inoculate one bottle at a time. Under aseptic conditions, the entire mulberry stem or cotton root, as the case might have been, containing vigorous growth of Phymatotrichum omnivorum, was taken out from the tube and introduced into the bottle in which the healthy plant grew. This was done by carefully removing the perforated cork of the bottle, which slid back with ease on the cotton stem (Fig. 9, a). Then a pure culture of Phymatotrichum omnivorum that had been grown on a sterilized mulberry stem in a test tube (Fig. '7, c) was introduced into the bottle and placed on the soil at the foot of the cotton plant (Fig. 9, a). With a sterilized cool/glass rod, this culture was gently pressed into the soil and the cork of the bottle closed again. Six bottles with six cotton plants were thus inoculated and two were left as checks. On January 3, 1922, wilting (Fig. 8, a andd) of all the inoculated plants became evident. "On January 4, wilting of the in- oculated plants was very pronounced. On January 5, the leaves began to shrivel. On January 10, the leaves of all inoculated plants dropped off (Fig. 8, b and e). When the inoculated plants were examined, they were all found to be killed and the foot end of the inoculated plant was overrun by Ozonium threads, whereas the two checks re- mained alive (Fig. 8, c) and remained so for five months, when they were used for other experimental purposes. Three of the inoculated plants were then chosen with a view of recovering the original fungus used for inoculation. The method employed was similar to that de- scribed for isolating the organism from infected plants secured from the field (see page 5'7’). The results of the re-isolations were posi- tive to the extent that out of 25 tube cultures made of the roots of these three inoculated plants, 14 yielded growth of Phymatotrichum omn-ivorum. The others did not show any growth whatsoever. Not content with the first series_of inoculations, it was decided to duplicate the experiments. Accordingly, on January 3, 1922, eight more healthy cotton plants, five weeks old, were secured and planted in sterilized soil in bottles, the same method being used here as was used in the first inoculation experiment. On February 3, 1922, four of the plants in the bottles were inoculated, the same method being used as was described in the first experiments, and four were left as checks. On February 6, all inoculated plants began to wilt, and on February 9 all inoculated plants were dead, exhibiting the typical root rot symp- toms as found in the field,-Whereas the checks remained alive. As in the first series of inoculations, the fungus was again recovered. From these artificial inoculation ‘experiments, it was proved for the first time that not only Pammel, but all the other workers referred to in TEXAS Roor R01‘. 63 this work, were correct in assuming that Ph/ymatotrichum omnivorum is the true cause of the so-called Texas root rot disease of cotton and all other susceptible hosts. These inoculation experiments seem to prove that Phymatotrichum omnioorum is the cause of Texas root rot. Natural Methods of Field Infection. We have already stated above that we have been able to induce artificial infection by placing the inoculum near the foot of a non-injured healthy cotton root. This would indicate that Phymatotrichum omnivorum is not necessarily a wound parasite. Duggar (5) believes that field infection is probably effected by penetration of the mycelium in the lenticles of the cotton roots. He further states that in all cases of infection, a depression of the bark on the root is immediately noticed, which would indicate the area of penetration of the organism into the root tissue. We have fixed and imbedded in paraffin over 150 specimens of cotton roots as well as sweet potato roots which show early stages of natural infection in the field. These imbeddings were made with the hope of finally sectioning and staining them so as to make out whether in- fection is by meansof fungus hyphae penetrating through lenticles in the roots, or through actual breaking through the epidermal cell wall. However, we have not as yet been able to section and stain these speci- mens ; hence these must be reserved for future work. Like Duggar (5), we have noticed time and again on okra, cotton, sweet potatoes, castor bean, and many other susceptible hosts that during early infections, there first appear slight depressions where freshly infected root touches the living healthy root and where the fungus threads of Phymato- trichum omnivorum bridge over from a recently infected host to a neighboring, adjacent healthy one. This depression is probably due to enzymic activity which the causal organism secretes before actually penetrating the host. This, however, is to be further verified by care- ful study. Repeated field observations on cotton seem to indicate two methods of infection: (a) The first method is that in which the main tap root is first affected. In this case the tap root usually comes into contact with some infected roots of a susceptible weed host in the soil. Once the tap root is infected, the disease spreads and advances upward, encroaching on nearly all the lateral roots and sometimes working up one or two inches above ground on the foot of the plant. (b) The second method is that in which one or more lateral roots are first at- tacked and the fungus gradually works and spreads downward to the main tap root and to the other laterals. In this case, infection of the laterals usually begins when roots of a healthy cotton plant which happen to touch the laterals of a neighboring cotton plant recently infected by the Texas root rot disease. This is the common occurrence in the field during the summer months. Whether infection starts first at the tap root or with the laterals, the infected herbaceous host suc- cumbs and is completely dead within two or three days after infection. With trees, it probably must require weeks and may be months before the causal organism is able to attack and to invade the great mass of the entire root system. A ‘ 64 BULLETIN N0. 307. NAME OF THE CAUSAL ORGANISM. Pammel (14) was the first to describe and to name the fungus of the Texas root rot disease as Ozonium auricomum Link. Curtis (3), quoting a letter from Professor G. F. Atkinson, then of the Alabama Agricultural Experiment Station, states (Atkinson’s statement): “The fungus was determined by Pammel as Ozonium auricomum, but I have my doubts about that being the proper determination and I think also that Pammel has.” "It is thus seen that Atkinson was practically the first to question PammePs correctness in naming the fungus of the Texas root rot disease. Shear (20), like Atkinson, did not think that PammePs Ozonium found in Texas was the same as the Ozonium auri- comum which is very prevalent in Germany. Fortunately, Shear (20) after his trip to Berlin and examining Link’s type of Ozonium auri- comum, convinced himself that this fungus was quite different from the one found by Pammel in Texas. Consequently, Shear renamed PammeYs Ozonium Ozonium omnivorum (Pammel) Shear. Accord- ing to Shear (20) both Ozonium auricomum and O. omnivorum slightly resemble each other in color but differ markedly in every other respect. Ozonium auricomum produces mycelium, which is more loose and lacks entirely the slender tapering branches which arise at right angles and which are so characteristic of Ozonium omnivorum. Ac- cording to Shear (20), Ozonium omnivorum is a species universally prevalent in the black lands of Texas, and furthermore, that Ozonium auricomum is also present in this state probably as a saprophyte. The writers have as yet been unable to find Ozonium auricomum. Suffice it to say that the above species is distinct from Ozonium omnivorum and, even if present in Texas, does not seem to be connected in any way with the true Texas root rot disease. It should be further added that Ozonium omnivorum is the namegiven to the sterile stage of this fungus. CONIDIA SPORE STAGE. Plant pathologists and mycologists in studying plant pathogens al- ways endeavor to work out and to connect up the various possible spore stages which the organism may have. This is not only valuable from a systematic point of view, but is of utmost importance in studying the life history of the parasite and the various methods with which it per- petuates itself. With reference to the Texas Ozonium, Pammel (15) believed it to be connected with some spore-forming Pyrenomycete. He based his conclusions on observations of infected sweet potato speci- mens on which he found typical Ozonium mycelium as well as numer- ous black perithecia-like bodies. Shear and Miles (21 and 22) state that the root rot fungus is suspected on strong circumstantial evidence of producing one or more spore stage forms through which it may be spread about broadcast. However, they neither described or named any such spore stages. Thornber (27) was really the first one to have met with and described a fruiting stage of Ozonium omnivorum, which occurred on affected alfalfa plants, but which he did not name. The following is his own statement: “It develops continuously on the ground along the outer margin of the zone of dying plants and TEXAS Roor R01‘. 65 immediately above the matted fungus mycelium which develops on the surface of the ground during hot, moist periods from July to September or October. This fruiting stage is developed and matures in the course of a few days, after which it disappears. It first appears as a flattened cushion-like filamentous mass varying in extent of about 2 to 10 or more inches in diameter, and about one-fourth inch in thick- ness. When young, it is creamy white in color, surrounded by a series of white radiating hyphae. With age it becomes light yellowish brown and soon breaks up into a fine powdery spore mass which imparts to the immediate area a characteristic, fawn color. Near the cushion is found the characteristic Ozonium mycelium. Among this mycelium appear hyphae Whose branches thicken at the extremities and the spores develop laterally and terminally, singly and in clusters. The spores are smooth, nearly colorless, globose to ovate. The spores range from 10 to at least 36 to the conidiophore, and these are growing over the entire swollen portion of the conidiophore. The spores measure about 4% to .7 microns in diameter. The conidiophores are about i492- to 25 microns in diameter.” Among the many other claims in connecting Ozonium with various fruiting stages of fungi, may be mentioned that of Schroeter, who be- lieved that some species of Ozonium developed into Ooprinus radians, one of the common toad stools. Penzig (16) believed that Ozonium developed into a species of Coprinus which he named Ooprinus inter- medius. Saccardo (17) and Winter (82) believed that Ozonium was connected with Agaricus deliquescens. Duggar (5) found the same conidial form in the field which Thornber had already found and de- scribed, but without naming it. Duggar decided that this conidial form belonged to the Hyphomycete group and to the genus Phyma- totrichum, which he named P. omnivorunt (Shear) Duggar. Duggar (5) connected up the genetic relationship of Ozonium omn/ivorum with Phymatotrichum omnivorum on the following observations: (a) the presence in the conidial layer of hyphae and strands (bearing conidia) found to be identical with the characteristic mycelium on the roots of affected plants; (b) the identity in artificial culture of a mycelium originating, on the one hand, on diseased roots and on the other, on the germination of the conidia as found in the field. It is thus seen that full evidence was lacking, because it was necessary to produce the Phymatotrichum stage from a pure culture of Ozonium omnivorum which was previously isolated from an infected plant in the field. This Duggar has not done. Duggar, however, was correct in his as- sumption that the Phymatotrtchum omnivorum fungus was the conid- ial spore stage of Ozonium, because the senior writer was able to pro- duce the conidiospore stage in a pure culture grown on steam-sterilized soil in a flask in the laboratory. Of six such flasks, one developed the typical Phymatotrichum omnivorum stage (Fig. 8, f and g). In the field, the conidia spores were at first formed on conidiophores at irregular intervals, which usually arise as short assurgent branches. The conidia are formed at the tip end of the swollen conidiophores. Later, spores are formed on any swollen branch of the various hyphae strands. Finally, spore production appears to involve practically the 66 BULLETIN No. 307. FIGURE 9. a. Showing" method of growing cotton plant in sterilized soil in bottle. The cork stopper is perforated and slides on the cotton stem without bruising it. To introduce the inoculum, the cork is moved up, and then pushed down again. b, c, d, h. and i. Photomicographs of typical strands of Phymatotrichum as found on infected plants in the field. g. Conidia spores of P. oqnmlvorum. f. Drawing of a strand to show structure and relationship of both young and old threads (f. and g. after Duggar). Texas Roor Ror. 67 whole mass of mycelium. This then Winds up in a pulverulent mass of conidia which are carried away by the wind. The conidia are sessile, or at best are formed on What may appear as minute sterigma. MORPHOLOGY OF PHYMATOTRICHUM OMNIVORUM. From a scientific consideration, the morphology of this organism is interesting, because such a knowledge helps to distinguish it from other closely related species. Our morphological studies, with but few exceptions, bear out Duggar’s (5) description. P. ontnivorum appears in five different forms. The first form is that of Rhizoctonia-like hyphae, made up of large cells (Fig. 10, g and h) which are formed in a stroma- like cushion. This condition is found both in pure culture (Fig. 11, a and b) and on the host, and resemble pseudo-sclerotia (Fig. 11, b). The individual mycelial cells (Fig. 10, g and h) are thin-Walled and frequently take on various shapes from round to elongated, hyalin to deep yellow. The second form is that of hyphae strands (Fig. 9, b to f, h, and i) which are found mostly on the surface of the affected host. These are made up of several to many anastamized fungus threads con- sisting largely of thick-Walled cells. These contain What appear to be various oils and food materials, Which give it the yellowish color. Because of their superficial location, the strands act as an anchor to the host and as means in ‘spreading the causal organism. According to Duggar (5), they may also function as conidial stroma. From the structure of these strands, the writers are inclined to believe that they not only are capable of withstanding the effect of drying a little longer, but they probably assist in absorbing moisture from the exterior sur- roundings. This assumption is based on observations of the organism in pure culture. These strands invariably groW out from the substrata on the inner surface of the glass (Fig. '7, e) where they are usually surrounded by drops of Water. The third is an acicular type, which on the host is invariably borne on the hyphae strands or on the pseudo- sclerotia. They consist of loose branches which are in pairs, that is, opposite and at right angles to the mother thread. Not infrequently, too, branching is verticillate. In either case, these branches are very characteristic in appearance, as they are needle-like, rigid, and taper to very fine filaments (Fig. 10, a to f). Duggar (5) states that this type is found only on the roots of infected hosts. We have repeatedly found it in pure cultures that are several Weeks old covering the sur- face of the pseudo-sclerotia Which form more or less abundantly When the causal organism is grown on various vegetable or agar agar media. However, this acicul.ar type of mycelium does not seem to be present in young cultures nor on the strands Which are abundantly formed on the glass surface in culture media. The Writers firmly believe that the function of the acicular type of mycelium is to serve as anchors of at- tachment of the hyphae strands on the root of the host which they pene- trate. The anchoring in this case is due to the penetration of these acicular branches into the host tissue. When numerous acicular branches meet, as they frequently do, they unite and form new secondary hyphae strands. The fourth is that of conidia spores (Fig. 9, g), which are formed at irregular intervals in the field and in pure culture (Fig. 6s BULLETIN No. 30v. 8, f and g). The morphology of the conidial spore stage (Fig. 9, f and g) was fully described by Duggar and bears no repetition here. Fifth, the senior writer has on one occasion met in pure culture with what appeared to be an immature ascus stage which failed to mature. Like- wise, Shear in a recent letter to us stated that he found another spore stage of Ozonium omnivorum, the nature of which was not disclosed. PHYSIOLOGY OF PHYMATOTRIOHUM OMNIVORUM. In the study of any plant disease which is induced by parasitic bac- teria or fungi, it is always helpful to study not only the disease itself, ¢ FIGUURE 10. a to f. Acicular type of mycelium of Phymatotrichum omnivorum. g and h. Rhizoctonia-like hyphae of P. omnivommn. i, j and k. Showing method of breaking down of individual cells of mycelial strands. This is quite common in pure culture and on the host. but also the behavior of the causal organism. Such studies may fre- quently throw new light on the limitations of the parasite and usually open the way for promising methods of control. Our studies on the physiology of Phymatotrqlchum omn/ivorum are as yet incomplete and will form part of a future publication. As a preliminary statement, however, it might be said that when this fungus is handled by begin- TEXAS Roor RoT. A 69 ners it is difficult to isolate. However, when once obtained in pure cul- ture, it will grow on a variety of food. Of the many kinds of media used, we found that it grows well on cooked beans, cooked rice, cooked Irish and sweet potatoes, cooked crushed cotton seed, mulberry stems, cotton stems, and roots, rose stems, chinaberry stems, and okra stems (Fig. '7, e to k; Fig. 11, a to e). It also grows well on soil agar,* bean agar, and potato agar. On vege- table plugs, especially on sterilized stems of cotton, okra, rose or mul- berry, growth in each case is slow, but later copious, white at first, forming a dense mat which seldom arises more than two or three mm. above the substratum and is never fluffy in appearance on the vegetable plug itself. The same is true when this fungus is grown on the other media mentioned; that is, growth at first is very slow, but after ten to fifteen days it becomes rapid and white at first, gradually turning yel- lowish-gray, with numerous pseudo-sclerotia-like bodies, formed singly or in large masses, fiat or slightly raised. When grown on bean or potato agar mediaj the pseudo-sclerotia appear as flufiy masses of mycelium scattered here and there, which are at first white, becoming yellowish-gray with age, and formed above the substratum and held by aerial mycelial branches. One of the peculiar characteristics of Phymatotrichum omnivorum in pure culture is the fact that on certain media it secretes black liquid drops (Fig. '7, i), which vary in amount with the media used. On ordi- nary cooked beans, for instance, or on crushed cotton seed, the black liquid drops become so numerous and abundant as to inundate the sur- . face of the culture. Another peculiarity of this fungus is the fact that it produces considerable water of condensation, which collects on the surface of the interior wall of the glass, and this surface becomes imme- diately invaded by hyphal strands which grow out from the substratum and cover the sides of the glass. These strands assume various forms of tree-like structure (Fig. '7, e). The fungus frequently attempts to produce pseudo-sclerotia on the strands on the glass, but these seldom develop to the same extent as they do on the substratum. Phymatotrichum omnivorum grows very poorly on sterilized soil (Fig. 11, c to be compared with a, b, d, and e), and in liquid media. It grows fairly well on potato starch, on which it forms a shiny, glossy layer which is fiat and compact. After two or more weeks of growth, the starch is broken down and a copious amount of liquid formed in the glass, the substratum changing color and becoming slightly yellowish to light ochraceous. We do not as yet know the conditions necessary for the development of the conidial stage in pure culture. As already stated, page 6'7, we have met with but one instance of conidia and that was in a pure culture grown on sterilized soil in 1000 c.c. Ehrlmayer flask (Fig. 8, f and g). Oonidia have also been obtained very sparingly on cultures *Made of 1000 c.c. soil broth decoction and 30 grams agar agar’. TIn every case (Where agar agar was added to the medium 30 grams of it was used to each 1000 c.c. of the liquid broth. '70 BULLETIN No. 307. ...... .. FIGURE 11. Pure culture of Phymatotrichum omnivorum, three weeks old, grown on soil b. Same as a, a. agar, showing strands, and beginnings of pseudo-sclerotia formation. but two weeks later, showing nature of flat growth with darkish fiat pseudo-sclerotia. c. P. ommvorum grown on steam-sterilized soil showing meager growth of scattered surface strands. (a, b, c, grown in 1000 c.c. Ehrlmayer flasks, the walls of which were broken off to make the photographs.) d. P. omnivorum grown on bean agar, and e. Grown on white potato agar. TEXAS R001‘ Ror. l 71 grown on various agar media, but in these cases the production of spores was very meager indeed. One fact remains very pertinent in connection with the conidia of Phymatotrichum omnivorum, and that is, that a satisfactory method of germinatingthem is still Wanting. Duggar (5) states, “Germination in any particular medium has been on the whole erratic.” We have made several attempts at germinating conidia spores, fresh material being secured from Professor Brown of the Arizona station, with practically negative results in every attempt. Various ways were adopted: some of the spores were plated out in agar agar media and others were inocu- lated in Van Tiegheim hanging drop cells in liquid broth made of soil decoction, in sugar solution, etc., with not a single instance showing germination. Professor Thornber of the Arizona station, in correspond- ing with the writer under date of December 21, 1921, states, “I made a careful study of these (conidia) as best I could and tried in every way possible to germinate them, but without success.” Professor Brown of the Arizona station, in a letter dated December 13, 1921, states, “I have made about-ten cultures on nutrient agar and none of the spores germinatec.” Dr. Shear in a letter dated February 28, 1922, states: “We have never had much success in germinating these spores. In fact, I am not sure that we ever actually demonstrated their ger- mination. Whatever growth we got might perhaps have arisen from bits of hyphae.” We have purposely referred to these statements of other workers to show that there must be some fundamental require- ment or condition favoring the conidia spores in nature, where they probably do germinate. This much is evident, that without being able to germinate the conidia, we cannot definitely explain their function. . It should be stated that in growing Phymatotriciium omnivorum in pure culture, we have tried vegetable plugs as tube cultures, agar agar media in petri dishes and on sterilized plant material. We found that after a comparatively short time-—say five or eightweeks,—the causal organism would dry up in tube cultures and more especially in petri dishes. However, when grown in Ehrlmayer flasks, whether using plant material or agar agar, we have been able to maintainthe fungus alive in the flasks for over six months without resorting to fresh transfers. We found that a 500 c.c. Ehrlmayer flask answered the purpose well. When agar agar was used, we placed 300 c.c. of the media in each flask, and when vegetable material was used, 100 to 200 grams. We have not, as yet, definitely determined how long Phyma- totrichum omnivorum will retain its viability in old cultures and whether it loses its power of infection when grown on artificial media for one or more generations. These are phases to be worked out in ~ the future. A further peculiarity of the P. omnivoru-m fungus is that the hyphal cells readily break down and die through plasmolosis of the cell con- tent. This is also met with under pure culture conditions when the older growth dies and is superseded by new cells (Fig. 10, i, j and k). '72 BULLETIN N0. 307. EFFECT OF THE TEXAS ROOT BOT DISEASE ON THE HOST. Mention has already been made on page 63 that, as a result of the first penetration and invasion of the causal organism, wilting begins and after twenty-four to forty-eight hours the epidermis and the cam- bium layer of the roots and the foot end of the affected plant become softened and in time may peel ofi’ readily. Shear and Miles (21) and Stevens (23) state that the fungus destroys the rootlets and the ex- ternal surface of the roots, invading the fibro-vascular system. The writers believe that the causal organism first invades the cambium layer, which results in the killing of the affected root. From the cambium, the fungus continues t0 Work inward into the fibro-vascular bundles and the pith. Dying of the host results after the tap root and most of the secondary roots and rootlets have been invaded. MYCOLOGIOAL FLORA ISOLATED FROM INFECTED DEAD COTTON ROOTS. Mention has already been made of the fact that a pure culture of Phymatotrichum omnivorum may be obtained from freshly infected cotton plants. However, as soon as the host has been thoroughly killed after a period of ten to fifteen days, the causal organism disappears and a rich mycological flora takes its place. The following fungi have been repeatedly isolated by us from dead cotton roots after the Phyma- totricltum omnivorum had disappeared: Fusarium; a species of Den~ dryphium, identified by Miss A. E. Jenkins of the United States De- partment of Agriculture, as D. cladosporoides, Ell. and Ev.; Cepha- lothecium roseum; Tricothecium roseum; Penicillium sp.; Aspergillus glaucus; Penic/illium glaucum; a species of Sphearopsis; a species of Alternaria; and a species of Verticillium. LIFE HISTORY STUDIES. From previous discussions, it is evident that nearly every phase of the Texas root rot disease, especially as it concerns practical methods of control are based on a thorough knowledge of the life history of Phymatotrichum omnivorum. In connection with these studies, it became apparent that control methods depended on a solution of the following phases: Is PHYMATOTRICHUM OMNIVORUM A STRICT PARASITE, A SAPROPHYTE, OR A SEMI-PARASITE? Pammel (14) believed that Phymatotricltum omnivorum might probably maintain itself from year to year as a saprophyte on dead organic matter. His conclusions were based on field observations at . Independence, Texas, where a number of cotton fields were badly in- fected with the Texas root rot disease during 1888. These same, fields were devoted to corn in 1887. Since corn was not a susceptible host, Pammel reasoned that the causal organism must have lived over in the soil or dead organic matter as a saprophyte. Furthermore, he be- lieved that the Phymatotricltum omnivorum fungus might probably live even on the dead corn stalks and roots. This, however, is not TEXAS Roor Ror. '73 true, and We suggest that the reason cotton dies in the fields where corn grew the year previous is that, as is generally the case, susceptible- weed hosts are nearly always present in the corn field and around the fences (Fig. 12, a to c, and Fig. 13, a), and these Weeds may main- tain the causal organism until the following year when cotton fol- lows corn. In order to definitely determine whether or not Phymatotrichum omnivorum remains viable on dead cotton or other susceptible hosts after they are killed by it, a series of experiments were undertaken with a view of ascertaining Whether or not it is possible to isolate the fungus from affected plants which were killed and remained dead in the field for various lengths of time. Of the many cultures carried out, only the 1921 data are given and these practically bear out the results of culture Work during 1919 and 1920. From Table 24, it is evident that Phymatotriclzium onmivorum seems to die with the even- tual death of its host, since at no time were We able to isolate a fresh viable culture from dead cotton plants or any other susceptible host after it had been killed by the disease more than ten to twenty days. Similar results are further emphasized in Tables 25 and 26. Table 24. Longevity of Phymatotrichum on undisturbed dead plants in the field. Per cent tubes Source of material Date cultured showing viable Phymatotrichum Freshly infected cotton roots . . . . . . . . . . . . . . . . . . . . . . . . . . . July 15 , 1921 1O Cotton roots killed by root rot andfremaining for'26 days undisturbed 1n the field . . . . . . . . . . . . . . . . . . . . . . . . . . . July 15 , 1921 0 Freshly infected cotton roots . . . . . . . . . . . . . . . . . . . . . . . . . . . Sept. 23 , 1921 9 Cotton roots killed by root rot and remaining for 40 days undisturbed 1H thefield . . . . . . . . . . . . . . . . . . . . . . . . . . . Sept. 23 , 1921 DOES PHYMATOTRICHUM OMNIVORUM LIVE OVER IN THE SOIL? In referring to the literature on Phymatotrichum omnivorum, one finds occasional statements to the effect that the causal organism of the Texas root rot disease does live over in the soil. Thompson and Wood (26) claimed that the causal organism of root rot of cotton (re- ferring to Phymatotrichum root rot) is capable of living over in the soil from year to year. However, no experimental data were given to support this statement. Duggar (5) in speaking of the strand hyphae of Phymatotrichum omnivorum states, “They are also more or less sclerotial and are doubtless an important factor in the persistence of the fungus in the soil.” It is true that Phymatotrichum omnivorum does produce on the host and in pure culture sclerotia-like bodies. These, however, are much of the nature of pseudo-sclerotia, and do not seem to be able to survive during the Winter months on a dead host or in the soil. All our evidence on hand tends to show that Phymatotrichum omnivorum is unable to live as such in the soil as ordinary mycelium Without the presence of a living host. If this were not so, a root rot spot one year would invariably mean a root rot spot another year if a susceptible host were grown again on that same spot. We have already referred on page 53 to the fact that very 74 BULLETIN N0. 307. FIGURE 12. a. Experimental corn field kept free from weeds through clean culture. b. The same field as a, but corn harvested and stalks cut down. Notice that in spite of the clean culture, there is scattered growth (in front and in right-hand corner) of Iponwea trichocarpa. c. An average corn field as it is infested by cocklebur and other suscep- tible weeds after the corn is made. Is there any wonder that Texas root rot hangs on where corn is used as a rotation crop? TEXAS Roor BOT. l‘ 75 frequently a root rot spot one year is not necessarily a root rot spot another year, if every susceptible host, including Weeds, happened to be killed out by the disease in that spot during the previous year. Those Who have studied the Texas root rot disease as it affects alfalfa FIGURE 18. a. Small-flowered Pink Morning Glory (Ipomoea trichocamsa) trailing on fences. In this way the survival of this weed is doubly insured, namely, by producing large quantities of seed, and through its fleshy undisturbed perennial roots in the soil. b. Ipomoea trichocarpa trailing on cannas and acting as a carrier of Texas root rot in the flower garden. c. View of a portion of a plowed up wheat stubble. One good rain after the plowing of the stubble land caused the Ipomoea trichocarpa to sprout from pieces of roots of this weed unharmed by the previous wheat crop. are familiar with the fact that a root rot spot increases in area as the years succeed. each other. In this Way there is not a single living alfalfa plant in the interior, although the disease spreads gradually from the interior of the spot to the outer periphery. Furthermore, in '76 BULLETIN N0. 307. order to minimize the losses from this disease, alfalfa growers are in the habit of re-sowing the dead spots in order to obtain some kind of a fair yield. Immediately, and as soon as this spot is re-sown, -the plants remain healthy and alive for nearly two years until the disease begins to work and crowd in from the exterior of the spot into the interior. If Phyvnatotricltum omnivormn could live in the soil inde- pendent of any living host, the reseeded alfalfa would have died the same year. As a further evidence, we might cite the following ob- servation. Ordinarily, we assume that when cotton is grown for a number of years on the same land that the Texas root rot disease would become worse from year to year. This, however, does not seem to be the case. On permanent cotton, and for a period of years, weather conditions being favorable, the disease fluctuates. If it begins mildly, it winds up with a high percentage of root rot and then grad- ually lessens. On the other hand, when the disease reaches the peak, it ends with very little root rot in the same field and then again in- creases. The reason seems obvious, because when the disease is at its highest during the summer, it generally succeeds in killing out not only most of the cotton but also the winter weed carriers, which nat- urally reduces the root rot to a minimum the following summer. This isrwell shown in Table 15 and in Fig. 14. It, then, seems pretty well evident that Phymatotrichum ownnivorum does not apparently live in the soil without the presence of a livi11g host. Even under pure culture conditions, the causal organism grows far better on nutrient media or on various sterilized vegetable plugs than it does on sterilized or unsterilized soil. In order todefinitely determine whether or not Phymatotrichum omnivorum does or does not live over in the soil in- dependent of a living host, it was decided to try to isolate the causal organism from the soil taken directly from badly infected spots in which the disease is very active and near cotton plants which had recently died from infection. This soil was secured from Substation No. 5, Temple, Texas, and brought into the laboratory within two days after it had been collected and was immediately cultured. The method em- ployed was as follows: One gram of soil was placed in a sterilized eight-ounce baby bottle to which was added 50 c.c. of sterilized water i equivalent to 1/50. The bottle was corked with a flamed stopper and shaken with an electric revolving apparatus for thirty minutes. Then with a sterile pipette, one c.c. of the 1/ 50. solution was taken out and placed in another sterilized baby bottle which contained 20 c.c. of sterilized water. This made a dilution equivalent to 1/100, that is, one gram of soil diluted in 1/100 c.c. of water. Again with a sterile pipette one c.c. of the original 1/ 50 was now put in a sterilized baby bottle which contained 200 c.c. of sterilized water, making a dilution of 1/1000, that is, one gram of soil to 1/1000 c.c. of water. This, then, gave two dilutions, one of 1/ 100 and the other 1/1000, both of which were plated out in agar media in the ordinary way and poured into sterilized petri dishes, some of which received an addition of one drop of a 5 per cent. lactic acid to prohibit bacterial growth while others were made without the acid. The plates from the 1/ 100 dilu- ~tion were marked A and the plates from the 1/000 dilution were TEXAS Room R01“. '77 marked B. Over 5000 such soil isolations were made of both series, A and B, and at no time were we able to find in even a single instance, growth of Phymiaitotrichum omnivorum. If this fungus lives in the soil, it would seem probable that from so large a series of soil platings we certainly would obtain at least a small percentage with viable cul- tures, but We did not. It is, of course, conceivable that strands of m R001" Rot m PERMANENT Corrow m“ 19m 19w 191a 1910 10201921 19m ‘IO s i: ‘ ’ m 4o ll/ l \/ its / 1\ IO_®_\ FIGURE 14. Graph showing the rise and fall of Texas root rot in permanent cotton from 1916 to 1922, inclusive. F represents plat No. F14; C represents plat No. C33; and A represents plat No. A61-70. Phymatotrichum omnivorum are occasionally found in the soil, espe- cially on the surface, in connection with conidia spores, but these un- doubtedly are strands which have been broken when pulled from the infected host, or strands which grew from the roots of an affected host which launched out in search of a neighboring host. From our own observations, we have never yet been able to find viable strands of 78 BULLETIN No. 307. Phymatotrichum omnivorum in the soil unless they were directly at- tached to an infected host or within its immediate neighborhood. This, then, seems pretty strong evidence that Phymatotrichum 0m- n/ivorum does not probably live in the soil as viable fungus mycelium without the presence of a living host. Neither is it apparently capable of living over in the soil as pseudo-sclerotia. Cultures of affected cotton roots showing the presence of these bodies as found on the dead roots and exposed in the field for several weeks or more did not yield any growth. If Phymatotrichum omnivorum is carried over in the soil, it is probably carried over as some form of spore stage which we have not as yet been able to determine or to verify. Unless further studies tend to show otherwise, it is safe to assume that Phymatotricltum omnivorum does not live over in the soil as a saprophyte, but that it needs the presence of a living susceptible host. HOW DOES PHYMATOTRICHUM OMNIVORUM LIVE OVER WINTER? In searching diligently through the literature, we have been unable to find a single statement as to how it lives over winter. During the first two years of our studies of Plz/ymlatotrichum omnivorum, we have observed time and again that the first severe frost kills 100 per cent. of all of the tops of the cotton plants, but the roots ofgthese plants are invariably unaffected and remain alive in the soil for the greatest part of the winter months. A great many of the wintered-over cotton roots were found alixre even as late as the following spring when the land was ready to be bedded _and planted again to cotton. Likewise, these roots would readily send out new roots and tops when placed in soil or in water (Fig. 15, a and c). Furthermore, we have also ob- served that such living roots when pulled out during the winter months do show evidences of Texas root rot infection at the‘ tip ends and that viable mycelium threads may actually be seen with the naked eye or cultured in the laboratory. I11 order, therefore, to definitely estab- lish whether or not the causal organism is capable of living over on roots of susceptible hosts during the winter months, it was decided to make a series of isolatio11s from infected cotton roots not only in the summer months during active growth of the cotton plant, but also during the winter months in which the roots remain alive but appar- ently in a dormant condition. The experiment was intended to find out whether Phymatmfrichum omnivorum would remain alive (a) if its infected host was pulled out and exposed to air-drying un-der lab- oratory conditions; (b) when the infected host is pulled out from the ground and exposed to air-drying of outdoor conditions, and (c) when the susceptible roots of a living host remain in the field undisturbed during the winter months. This latter experiment especially has a practical application inasmuch as it is customary among tenant farm- * ers, especially negroes, to leave their cotton fields undisturbed after the last picking of the cotton and to plow up that field very late in the winter, or just before planting time the following spring. Texas Roor Ror. 79 Table 25. Viability of Phymatotrichum omnivorum asinfluenced by exposure of infected cotton roots to indoor con-ditions. Date when Date when Per cent of Date when Date when Per cent of pulling culturing tubes showing pulling culturing tubes showing infected material in Phymato- infected material in Phymato- roots laboratory trichum roots laboratory trichum July 10, 1921 July 15, 1921 11 2 Nov. 17, 1921 Mar. 15, 1922 O July 10, 1921 July 30, 1921 2 4 Nov. 26, 1921 Nov. 30, 1921 9.6 July 10, 1921 Aug. 10, 1921 0 Nov. 26, 1921 Dec. 29, 1921 0 Aug. 15, 1921 Aug. 19, 1921 8 8 Nov. 26, 1921 Jan. 18, 1922 0 Aug. 15, 1921 Aug. 29, 1921 4 Nov. 26, 1921 Feb. 15, 1922 0 Aug. 15, 1921 Sept. 16, 1921 O Nov. 26, 1921 Mar. 15, 1922 O Sept.19, 1921 Sept. 23, 1921 6.4 Dec. 3, 1921 Dec. 7, 1921 4 Sept. 19, 1921 Oct. 2, 1921 4 Dec. 3, 1921 Dec. 14, 1921 3.2 Sept. 19, 1921 Oct. 26, 1921 0 Dec 3, 1921 Jan. 1 , 1922 0 Oct 9, 1921 Oct. 14, 1921 7.2 Dec , 1921 Feb 15, 1922 0 Oct 9, 1921 Oct. 28, 1921 1.6 Dec , 1921 Mar 15, 1922 0 Oct. 9, 1921 Nov. 20, 1921 0 Dec 10, 1921 Dec. 4, 1921 2.4 Nov 4, 1921 Nov. 8, 1921 11.2 Dec 10, 1921 Dec 22, 1921 1.6 Nov 4, 1921 Nov. 19, 1921 0.8 Dec 10, 1921 Jan 18, 1922 O Nov 4, 1921 Nov. 30, 1921 0 Dec 10, 1921 Mar 15, 1922 (J Nov 4, 1921 Dec. 14, 1921 O Jan 12, 1922 Jan 8, 1922 7.2 Nov 4, 1921 Jan. 18, 1922 0 Jan 12, 1922 Feb 15, 1922 0.5 Nov 4, 1921 Feb. 15, 1922 0 Jan 12, 1922 Mar 5, 1922 0 Nov. 4, 1921 Mar. 15, 1922 0' Feb 1 , 1922 Feb 15, 1922 1 Nov.17, 1921 Nov. 21, 1921 5.6 Feb 12, 1922 Mar 15, 1922 1 Nov.17,l921* Dec. 29, 1921 O Feb 12, 1922 Mar 28, 1922 0 Nov.17, 1921 Jan. 18, 1922 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Nov. 17, 1921 Feb. 15, 1922 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Table 26. Viability of Phymatotrichum as influenced by time exposure in the field of freshly infected cotton roots. | l l Date of No. of l l Date of Per cent of pulling killing l Date of killing frosts l culturing tubes showing infected frosts l during exposure ‘ material in Phymato- roots during l l laboratory trichum exposure l l l l _ _ Nov. 15, 1921 14 lNov. 19, 1921, Nov. 20, Nov. 21, l l Nov. 28, Dec. 5, Dec. 10, Dec. l 11, Dec. 12, Dec. 18, Dec. 24, l Dec. 25, Dec. 26, Jan. 5, 1922, Jan. 12, 1922 . . . . . . . . . . . . . . . .. Jan. 16, 1922 O Nov. 15, 1921 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Nov. 18, 1921 3 Dec. 21, 1921+‘ 2 l . . . . . . . . . . . . . . . . . . . . . , . . . . . . . .. Jan. 1s, 1922 0 Dec. 27, 19ml 0 l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Jan. 2, 1922. 4.5 *After being pulled, the plants were left in the field until November 28, 1921. The tops were then cut off and t_he roots placed in the weather ca e at Substation No. 5, Temple, Texas. TThese giants before being pulled went through 12 illing frosts, killing the tops without affecting t e roots. The dead tops were clipped off, and the living, infecte roots were placed in the weather cage at Substation No. 5. That Phymatotrichum omnivorum is unable to remain alive very long after its susceptible host has been pulled out from the ground and exposed to drying of indoor conditions, is shown in Table 25. From this table it is seen that every time a freshly-infected host Was pulled out from the ground and isolation cultures made, a certain percentage of viable cultures of Phymatotrichum omnivorum was obtained; that on the other hand, and just as soon as the roots were pulled out, and exposed to drying under indoor conditions, the causal organism would die within ten to twenty days. This is true no matter what time of the year such freshly-infected roots are pulled out and exposed to dry- ing. The same is also true when freshly-infected roots are pulled out and exposed to drying of outdoor conditions. This is shown in Table 26, which is self-explanatory. From these two tables, it is evident that 8O BULLETIN N0. 307. the organism dies with the death of its host. However, Phymatotrichum omnivorum remains alive during the entire winter on cotton roots in a field if infection has taken place during a winter which does not result in the complete killing of the host, and if the roots are not pulled out from the soil as shown in Tables 24 and 2'7. From Table 27, it is seen that when live cotton roots remain undisturbed in the field dur- ing the winter months, they will show a higher percentage of infection the longer they remain in the field. * From the above studies, the following deductions are made. During the summer months the Phymatotrichum omnivorum fungus dies with the death of its host and to maintain its further existence, it must reach for the roots of neighboring healthy susceptible hosts. This actually occurs in the field from early in March until the first killing frost in the fall. During the winter months the causal organism is not as active as during the summer, but it nevertheless spreads slowly by contact from living root to root of cotton and perennial weeds, and maintains itself by invading only part of the root, killing only the parts attacked. Furthermore, during a wet fall, when fall plowing does not kill the cotton roots, or if plowing is delayed until the following spring, the disease will be given the best means to maintain itself during the winter months. This is seen in Table 2'7, which shows conclusively that the causal organism remains active during the entire A winter, if given a live host, though it seems to work much more slowly in winter. S1 TEXAS R001‘ RoT. 0.00:0 8. ‘H0000 0.00» 0.0» :0 00072400 40:02:05,400 00300 00. £000 20000000 S.:0:00m~.00v. 0200202 00. 5E 1000.003‘ 0. :00 02 000» . W00. 000» E000 o». 300% E000. W044 Z0. W004 .20. 300$ W00? 160$ W030 .0:40 0:40 500.8 . 0:40 0:40 0:40 I030 0001.03.00 5000.20 080 500F300 000200 0000 20mg 8000.6 0.020 000.. @0300. A6000. 00300. . . . . . . . . . . . . . . . 0 3 m0 o w w ww 0 00200 . . . . . . . . . . . . . . . . w 8. 8 0 0 m w» o 00.300. . . . . . . . . . . . . . .. 0 . . . . . . . . . . . . . .. . . . q o 30 0. 00...»00......... . . . . . . .. 0 . . . . . . . .. .. . . . . .. .. 0 0 S0 O ~000~000~20>000~00..... . . . . . . . . . . . 0 0.0. 00.0 0 . ~005000~20:02=00..... . . . . . . . . . . . . . . . . . .. w 5 M0 .0 >00: 0. Zww >01: S. :00 . w=€$so= Z0. m. AMBEPrAdxmm. . . . . 00300 . . . . . . . . . . . . . . . . 0 w» 0w ww 0 0 00.3 00.00. 00500.. . . . . . . . . . .. . .. . . . . . . . . . . . . . . . . . . . . . . . .. m. 0 00.0» 3.5 00030.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. 0 0 00.00 0.0.3 $55000 0260000200. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . w “$15 00.00 0 82 BULLETIN No. 307’. WINTER CARRIERS OF THE TEXAS ROOT ROT FUNGUS. In the early part of this Bulletin, page 19, we have already referred to the large number of hosts which the Texas root rot disease is capable of attacking during the summer months. We have also shown that the causal organism continues its activity, although more slowly per- haps, during the winter months on roots of certain susceptible hosts. It should not be forgotten that of the large number of hosts which are susceptible to the Texas root rot disease during the summer months, many are fortunately annuals which cannot hibernate the causal organ- ism because they die with the first fall killing frost. Such plants can- not, therefore, act as carriers of the Phymatotrichum omnivorum fun- gus, because as we have already shown, this organism is apparently incapable of maintaining itself on a dead host. It is, therefore, of extreme practical importance to determine which are the biennial or perennial hosts whose roots are capable of maintaining the causal fungus during the winter months, because 0n this point depends the success in control methods. If we are to succeed in controlling the Texas root rot disease, We must have definite methods of eliminating entirely from the soil all living roots of all susceptible hosts, whether cultivated or weeds, during the winter months. To allow the causal organism to maintain itself during the winter is merely to give it a chance for a new lease in life the following year. Our studies, so far, have definitely established the fact that the following hosts are winter carriers ‘of the Texas root rot fungus: cotton, okra, pepper, sweet po- tato, carrots, beets (garden or stock), wild morning glory roots, Ipomoea. trichocarpa (Fig. 5, d to g), and susceptible shrubs and trees, whether ornamental or fruit. In this case, the causal organism attacks the living but dormant root and it is capable of slow but steady spread. This is seen in Table 27, which shows that the disease is active on cotton and on I pomoea trichocarpa during the winter, but it cannot be detected since all tops are killed by frost, and hence there is no wilting apparent. The following spring when the land is plowed up and devoted to a susceptible crop or even to a non-susceptible crop, but one in which susceptible weeds are permitted to thrive without molestation, the causal organism may continue its activity without in- terruption. It is especially peculiar with Ipomoea trichocarpa that cutting off the top of this plant with a hoe or cultivator during active growth does not necessarily kill the roots. These, on the other hand, will soon send out new sprouts and continue to thrive (Fig. 15, f). WHAT IS THE BEST TIME FOR FALL PLOWVING? When it had been established that Phymatotrichum omnivorum passes the winter on roots of susceptible hosts, some preliminary tests were carried out with a view of determining which was the best time for fall plowing in order to destroy the roots of the cotton. We have already referred to the fact that Shear and Miles (21 and 22) have claimed that fall plowing controls root rot and we have also referred to our own work, Table 12, in which we have indicated that as long as the roots of the cotton are permitted to remain in the ground, fall TEXAS Room Ror. 83 plowing Will have little effect on the control of Texas root rot. This does not mean that we were ready t0 condemn fall plowing, but it became more and more evident that we were in need of a cultural method which would permanently destroy the cotton roots and thus prevent them from becoming carriers of the causal organism during the winter months. We have repeatedly observed as we have studied fall plowing carried out by various farmers in Bell County, for a period of several years, that actual fall plowing does not necessarily kill the cotton roots as long as the soil is moist. On the other hand, fall plow- ing during a period of drouth during the fall actually kills a large per cent. of the cotton roots because in this case the disturbed roots remain in a dry mulch, and for lack of moisture, they fail to revive or to strike new rootlets. This means that we may sometimes control root rot through fall plowing if the plowing is carried out during a period of prolonged drouth and not during a rainy spell as is frequently done in the fall by the majority of farmers. In order to test this out, a field was selected which was practically free from the Texas root rot disease. Such a healthy field was necessary in order to determine the effect of the plowing on killing healthy non-infected cotton roots. The field chosen for this experiment was Plat G 1-10 at Substation No. 5, which only showed a trace of root rot. The results are indicated in Table 28. From this table it is seen that the first plowing carried out during November 21, 1921, resulted in the actual killing out of 96 per cent. of the cotton roots. In this connection it should be stated that this plowing was done during a dry spell and that the soil itself was very dry during the plowing and for some time after plowing. On the other hand, the second plowing, which was carried out on December 19, 1921, resulted in killing only 12 per cent. of the cotton roots; the plowing done on December 21, 1921, killed only 8 per cent. of the cotton. In both of these last two plowings there was consid- erable moisture in the soil from previous rains and this explains the small percentage of dead cotton roots in spite of the plowing at that time. These percentages were obtained on January 29, 1922. In fur- ther referring to Table 28, and to the percentage count taken during February, 1922, one will see that the greatest percentage of dead roots resulted from the early plowing on November 21, which was done dur- ing a dry spell. Table 28, although representing only preliminary plowing tests of one year, nevertheless points to a very promising method of control; namely, that cotton growers should watch weather conditions and plow up the cotton only during a dry spell in the fall and after the last cotton picking. If this is not possible, as is often the case during a wet fall, a different procedure is to be tried, which will be referred to under “Control” on page 90. 84 BULLETIN N0. 307. ‘ FIGURE 15. a. Cotton root as it lives over in the soil during the winter. The blackened top shows part of the dead stem killed by frost. b. Soil thermometers for studying soil temperatures. c. Same root as a, placed in water in the laboratory to show that it is alive and capable of sending out new roots. d. Blossoms of Ipomoea trichocao~pa to show the prolific nature of this weed. e. Fleshy trailing perennial root of Ipomoea trichocarpa, f. Root of I. tr/ichocarpa with the top cut offrby hoe, and the appear- ance of new sprouts. g. Leaves, seed pods, and seed of I. trichocarpa. h. Leaf, seed pods, and seed of Ipomoea hederagea, an annual weed. TEXAS Roor Ror. 85 Table 28. Field killing of cotton as affected by time of plowing during the fall months! Per cent of live or dead roots as a result of fall pjowing during Date of fall plowing Jan. 29, 1922 Feb. 9, 1922 Per cent Per cent Per cent Per cent live roots dead roots live roots dead roots Nov. 21 , 1921 . . . . . . . . . . . . . . . . . . .. 4 96 8 92 Dec. 19, 1921 . . . . . . . . . . . . . . . . . . .. 88 12 52 48 Dec. 31, 1921 . . . . . . . . . . . . . . . . . . . . 92 8 68 32 *The cotton field of this experiment c-1-10 was practically free_ from Texas root rot. The dead plants referred to in Table are those killed as a result of disturbance 0r exposure from plowing and not from Texas root rot. or WHAT IMPORTANCE ARE THE CONIDIA SPORES IN’ THE LIFE CYCLE or PHYMATOTRIOHUM OMNIVORUM? We have already referred to the work of Thornber (27) and that of Duggar (5) and our own in which we have shown that we have already obtained conidia of Phymatotrichum omnivorum from a pure culture grown on sterilized soil in the laboratory. Under discussion of the physiology of Phymatotrichum, page 68, it has already been stated that attempts at germinating the conidia of this fungus failed. It is, therefore, difficult to tell just what role they play in the life cycle of the causal organism. Are they capaable of germinating only immediately after they are formed or are they able to retain the germination power a long time and thus pass the winter months in a dormant ‘condition? How important are these spores in spreading broadcast the causal organism in the same field and from field to field and from state to state? The-se questions will be answered only when a satisfactory method of germination is developed. In the meantime, it is safe to assume that the conidia, at "least in the summer, do help to spread about the causal organism, but to what extent is as yet unknown. . HOW noes ournoon AND SOIL TEMPERATURES DURING THE WINTER MONTHS AFFECT THE LIFE CYCLE or PHYMATOTRIOHUM ~ OMNIVORUM? References have already been made to the possible influence of out- door and of soil temperatures during the growing months in the sum- mer. We have also referred to the fact that while the first killing frost during the fall immediately kills all the top parts of the cotton plant and other susceptible weeds, the roots of these plants usually remain alive and pass over the winter months in great numbers. We have further shown that during the winter months the causal organism is active, although to a lessiextent than is the case during the summer months. We have also indicated that infection may take place at any time during the fall and winter months. It became necessary to study the soil temperatures, during the coldest days of both fall and winter with a view of gaining some idea as to why both the roots of the sus- ceptible host and especially the causal organism itself are not killed in spite of low outdoor temperatures. The soil temperature studies 86 BULLETIN N0. 307. were continued during the fall and winter months for a period of several years. We shall, however, refer only to studies during 1918 which are typical. From reference to Table 29, it is seen that during the coldest days in January, November, and December of 1918, no matter how cold the outdoor temperature was at any one day, the soil temperatures, especially those of 24 to 4L8 inches deep, never went be- low 59 degrees Fahrenheit. Because of this fact it becomes very evi- dent that the relative moderate soil temperatures during the fall and winter months protect the cotton roots or the roots of other susceptible hosts from dying. This also explains why the causal organism itself is not inhibited, but instead is still capable of activity during the winter months irrespective of outdoor weather conditions. 87 TEXAS R001‘ Rom.‘ H.555? ww. mo: 555565.555 wowmmummlLiwmicm 255559. 55.5w 5w5m m» M55555 Zo. m. .5655? 525m. 5<5 55 055005. 5 5055 m 5055mm m 55mm 5w 505E w~5 525w mm 555w ~5m 55.55am o5» . .5355? .5<55- .5555? 5S5- .5<5x| 5S5- .5557 .5<55| .755? .755- .3557 .755- .3557 .5<5.5| .5<55T .5<55| _5:5 55:5 5E5 55:5 55:5 _5:.5 5E5 55:5 .5555 555.5 5E5 55:5 55:5 _5s5 5555 5E5 555555 .m . . . . . . . . . . . . . . . . . . . . . . . . .. m0 ww m0 Q0 Qm Qw Q~5 Qm Qw Qw Qw Q5 Q0 mw mm mm 5555555 Q . . . . . . . . . . . . . . . . . . . . . . . . . . mQ 5m m5 mw mm m5 Q0 m Q0 mQ. 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Considering the importance of the Texas root rot disease as it affects many economic crops, it is necessary to know whether or not this organ- ism is carried about with cotton seed or the seed of any other sus- . ceptible host. There are but two possible ways in which it might be carried with the cotton seed, namely, with fungus hyphae and with conidia. In previous discussion, page 14, we have already shown that Phymatotrichum omnivorum attacks only the roots of its host, and as far as is known none of the parts of the plant above ground. Further- more, the fungus dies as the result of drying. This, then, would re- move entirely the possibilities of its being carried as adhering mycelial threads on the exterior of the seed coat or even in the interior of the seed itself. There remains, therefore, one possibility and that is that the conidia of Phymatotrich-um omnivorum may be carried on the exterior of the seed coat of cotton seed as viable spores. Proof of this, however, is lacking and it is very doubtful whether this actually is the case. Pammel (15) actually sowed seed from infected plants which had died from theTexas root rot disease. He found that, from the seed germinated, in no case did the Texas root rot appear, al- though, as he states, many of the seedlings died from otherrots. In our own work (Table 2), we have already referred to the fact that plantings made of cotton seeds from both healthy and afiected plants germinated and in no case did the Texas root rot appear. Unless fur- ther research prove different, and we do intend to look into this matter more thoroughly, it is safe to make this statement, subject to change, that Phymatotrichum omnivorum is not probably carried over on the seed as viable conidia. If it were, the disease would certainly be intro- duced in many of the Southern States where Texasroot rot is at yet unknown, since Texas is exporting a great deal of seed cotton to the many other Cotton States. SUMMARY <55 LIFE HISTORY. From the above studies, it is safe to summarize the life cycles of the causal organism as follows: Very early in the spring (beginning, say, in March or April) Phymatotrichum omnivorum is found to be active underground and to infect the roots of the morning glory (Ipomoea trichocarpa) or other susceptible weeds. During the latter part of April and the first part of May, many of the cockleburs in the ground have germinated and some of the seedlings are fairly well ad- vanced in growth. When these plants are pulled out, some of them will be found to be infected with the Texas root rot disease. The in- fection in this case may be traced to the dormant but infected roots of the morning glory (I pomoe trichocarpa) in the soil which happened to be near enough to the roots of the young cocklebur plants. In this case, the infection of the cocklebur roots is more or less localized to the secondary rootlets or to the tip end of the main root without, ap- parently, killing outright the young weed itself. As the season ad- vances and when cotton is planted, the young plants may become in- fected if they happen to be near enough to previously infected roots TEXAS RooT Rotr. 89 of Ipomoea or the cocklebur. This latter weed may be killed by cul- tivation, but the roots of I pomoea trichocarpa remain alive, although its tops are cut off (Fig. 15, f) when the soil is Worked. It is, there- fore, the continual presence of the roots of this wild morning glory or of other susceptible Weeds in the cotton patch that insures infection of the cotton plants during the summer months. Once the cotton becomes infected, the disease begins to spread, slowly at first and more rapidly later, depending on the season. In this way, the disease con- tinues to spread during the summer months, attacking and killing not only cotton, but also other susceptible annual or perennial hosts. In this connection it is strange that although cotton, okra, black-eyed peas and many other hosts are killed outright when infected during the summer months, the morning glory (Ipomoea trichocarpa) ex- hibits a decided resistance in the sense that although infection does take place, the disease remains localized to certain parts of the roots and kills only a small percentage of the affected plants. In Bell County, this Weed is one of the worst pests, carrying as it does the, causal organism of root rot during the winter months, as well as dur-' ing the summer. In this case, it acts as a bridge-over to carry the infection to the cotton or other susceptible hosts Which it meets in its Way. The rapidity of the spread of Texas root rot during the summer months depends on the amount of rainfall during July and August, and to a certain extent on the root system of ‘the host itself. Fields of black-eyed peas, for instance, when sufficiently advanced, may be killed out to an extent of 8O to 100 per cent. The same is true of okra, castor bean, alfalfa, sweet clover, and other susceptible hosts which possess a well-developed system of lateral roots. With cotton, on the other hand, the spread of the disease will depend on the fertility and moisture conditions of the soil, both of which directly influence a scant or copious root system. For this reason, during a dry summer, there may be very little Texas root rot in cotton and a tremendous amount in sweet clover, for instance, all because of a dif- ference in root system, the latter favoring root contact in the soil, and the former not. ' In the fall, just as soon as the first frost kills the tops of the cotton plants as well as the tops of all other perennial, susceptible hosts, it becomes difficult if not impossible to tell outwardly whether or not the Texas root rot disease is active. However, although the tops of these plants are killed by frost, the roots in many cases remain alive and afford a means for the causal organism to live on. These roots act as carriers of Phymatotrichum, ominiworum, and help it to live over the winter months. It is, therefore, seen how unsafe it is not to de- stroy the roots of cultivated susceptible hosts as well as those of the weeds. Methods of accomplishing this are indicated under “Control Methods” on page 90. It cannot be emphasized too strongly that con- trol methods must depend on a thorough knowledge of the hosts which carry over the causal organism during the winter months. When this is definitely established, the next step is to develop practical "methods in destroying these winter carriers. For instance, it is not an easy matter to destroy the perennial roots of the morning glory (I pomoea 90 BULLETIN ‘No. 307, trichocarpa), which constitutes such a menace in many counties in. Texas. It may turn out to be a more difficult task to eradicate this Weed than the Texas root rot. On the other hand, there are prob- ably other perennial Weed carriers in Texas Whose destruction may e not be as difficult. This will be determined by later studies. l As soon as the causal organism passes the Winter months on the a roots of living susceptible hosts, either cultivated plants or Weeds, it starts anew its life cycle in the spring and summer months in a man- ner outlined in the beginning of this summary. It seems very doubt- ful Whether the causal organism can maintain itself in the soil with- out the presence of a living host. Consequently, the eradication of the causal organism and the control of the disease becomes a possibility i and in fact a reality as We shall soon see. METHODS OF CONTROL. What is uppermost in the minds of cotton growers in Texas is how % to control the ravages from the Texas root rot disease. There have 5 been various claims from time to time as to the best methods of con- trolling this disease. We have already referred to the Work of Shear and Miles (21 and 22) and to the fact that deep plowing has gener- ‘ ally failed to control the disease. We have also shown that deep plow- ing in the fall Will not control root rot as long as the cotton roots remain in the soil during the Winter months and if the land happens to be moist during the plowing time. There also have been various claims made especially by Shear and Miles (21 and 22) to the effect that crop rotation will control the Texas root rot disease. We have already indicated the fact that crop rotation did not in most cases give results hoped for. No control methods for the Texas root rot are possible unless these methods are based on a thorough and fundamental knowledge of the life history of Phymatotrichum omntoorum, the cause of the Texas root rot disease. We have gone at length to present every bit of evidence obtained through systematic and careful research, evidences which are based altogether on the study of the life cycle of the Texas root rot fungus. Our recommendations for controlling the Texas root rot dis- ease, therefore, are based entirely on the results of these studies, and it is believed that although future Work may to a certain extent pos- sibly modify some of our present recommendations, yet we feel that the main features of the life cycle of Phymatotriclzum omnivorum as worked out justify the following recommendations: In the light of our present knowledge, it seems evident that as long as the Texas root rot disease is perpetuated during the Winter months on living dormant roots of the cotton, okra, and some of the roots of perennial Weeds, it is certain that this disease will reappear during the following summer if a susceptible crop is grown on that land and weather conditions are favorable. Even though non-susceptible crops such as cereals or grain are grown on that land as a rotation, the root rot disease may reappear if we overlook the fact that through a lack of clean culture which would permit the development of susceptible Weed hosts, Texas root rot will have a chance to thrive as though TEXAS RooT RoT. 91 cotton had been grown there. It becomes, therefore, clear that the first attempt at controlling the Texas root rot disease should aim to kill out during the fall and Winter months not only the roots of the cotton plants Which ‘ remain alive in the Winter months in the soil, but also the living roots of perennial Weeds. This, it seems to us, is the key- note to practical methods of controlling the Texas root rot as it ap- plies to the cotton and to the many other herbaceous susceptible crops. In attempting to control the Texas root rot disease, We should con- sider two methods of procedure, determined by Whether the ‘fields are (a) badly infected, or (b) slightly infected, each case requiring a different treatment. CONTROLLING TEXAS ROOT BOT DISEASE IN BADLY INFECTED LANDS. Assuming that during 1921 a cotton field had died to an extent of '70 to 80 per cent., What are We to do? Immediately after the last pick- ing of cotton is made during the fall of 1921, the cotton plants should be killed, by being pulled out and exposed to the air for drying. This may be done With a “middle buster” or the kind of plow that is used to dig out sweet or Irish potatoes. Such a plow will uproot the plants and expose them to air-drying. If all the cotton roots have not been exposed by this plowing, they should actually be pulled out, the farmer using the cheapest possible methods at his command to accomplish this. Sometimes hand pulling may be equally as cheap. The pulled- ~out cotton plants should remain in the field for about a month or six Weeks and exposed to at least one or more severe freezes. The ground could then be plowed 5 inches deep and all trash, dead cotton stalks and roots Worked under. In this case there Will be no difficulty what- soever in turning under .the refuse of the dead cotton plants because -dead cotton plants subjected to the effect of one or two freezes will break up very readily when gone over with a harroW. This second plowing should in preference be carried out during a dry spell, al- though it is not always necessary if Weather conditions will not permit it. The land so plowed should remain untouched for a Week or two, -or longer, without being harrowed or disced until all growth, especially weeds, has been dried and killed. After this, the land should be disced and left alone for two or three weeks until evidence of weed growth begins to appear. Such a condition may be looked for in some of the southern parts of the State. Immediately, and as soon as new weed growth appears, the land should be disced and harrowed to a depth of about three or four inches so as to make a fine top mulch. The field will then need no further treatment until February, 1922. At that time, the land should be plowed again about 5 inches deep, exposed for a Week or two for drying, and then disced, harrowed, and planted to oats. The oat crop xvill be ready to be harvested during May or June of 1922, depending on the locality, and immediately after har- vesting (not later than one or two weeks) the stubble land should be plowed up to a depth of about five inches. All through the summer and fall months, the now-fallow land should be given frequent cultiva- tions (three or four inches deep) so as to keep d‘own every pos- sible weed growth, especially to uproot and to expose the roots of 92 BULLETIN No. 397. the morning glory (Ipomoea trichocarpa). During the fall of that year (1922) that land may be plowed up and planted t0 wheat. The following spring of 1923 and after the Wheat is harvested, the land is again plowed to Work under the stubble and this is followed by fre- quent cultivations during the summer, fall, and winter months so as to keep down every possible growth of weeds. During the spring of the third year, that is, 1924, the land should be free from Texas root rot and ready for cotton again. The above drastic control measure, it is seen, calls for a succession of plowings and shallow cultivations during the fall and'winter months so as to kill out all possible weed carriers. A more drastic method may be applied in dealing with a badly infected field and that is, to leave the land fallow the first year. In- stead of devoting the infected land to some grain immediately after the cotton crop, the land is kept fallow for one year, in which the soil is persistently worked and cultivated to keep down all possible growth. The loss in crop during the fallow year will be more than compensated in the increase of cotton the next year. This drastic measure may not always be necessary on lightly in- fected fields. For this reason each farmer should pick out his worst infected land and adopt this method of one year fallow together with persistent cultivations. His other fields which are less infected may be treated as hereinafter indicated. There are regions in Texas where wheat and oats do not thrive. These regions include parts of the extreme southern and southwestern counties in Texas and counties in the Central Gulf Coast region. There the procedure under these drastic methods would consist in a one-year fallow accompanied by clean culture. After that the land may be devoted to corn, sugar cane, or resistant truck crops such as cabbage, lettuce, spinach, or onions. This is true especially for the Rio Grande Valley. When the land has thus been cleared of the Texas root r_ot, it may then be devoted to alfalfa, or even cotton. In carrying out the drastic treatment and keeping in mind the clean culture idea, we should not overlook the fact that trees and certain- perennial shrubbery around the edges of the field may act as per- vsistent carriers of the Texas root rot disease. If these are permitted to remain unmolested, all our efforts at clean culture or at fallow clean culture may be practically defeated. It is, therefore, of extreme im- portance that all turn rows and all hedges on the roads should be persistently clean-farmed every year. Once a field has been cleared of the causal organism of Texas root rot, any one system of crop rotation may be adopted that is best suited to the particular locality in which the Texas root rot disease is preva- lent. Here, too, we must-insist that in starting with a clean land and with a system of rotation, one should never neglect clean, culture; if he does, the land will be reinfected. We shall soon suggest a few pos- sible systems of rotation to be adopted after the land is cleared of the Texas root rot. Each farmer will modify these rotations to suit best crop conditions of his own locality. As regards controlling Texas root rot in fields which are lightly TEXAS R001‘ R01‘. 93 infected, there is but one thing to do and that is to kill out both cotton plants and perennial roots of susceptible weeds during the winter months, carrying out the cultivation idea as outlined above and then devote that land to some system of rotation, the kind of which will depend on the locality and the inclination of the farmer, the clean culture idea always being kept in mind. , Sometimes a one- year rotation of corn, or sorghum, or any other of the grain crops in which the land is plowed under and clean fallow practiced during the fall and winter months, will accomplish the desired results. Beginning with a field which was cleared of root rot, the following system of rotations are suggested: One-Year Rotation. 1921——C’otton. 1922—Either corn or grain sorghum; or wheat planted in the fall; or oats planted the previous fall or spring; after the grain crop has been harvested, the land is to be plowed up and all stubble worked under, and during the summer, fall, and Winter months frequent cultivations given to destroy all weed vegetation. 1923—U0tt0n. Two-Year Rotation. 1921—C’otton, followed by wheat or oats in the fall or oats in the spring ' of 1922. 1922——When the wheat or oats are harvested the land is devoted to clean fallow during the summer, fall and winter months. 1923—Corn, followed by clean culture during the summer, and clean fallow during the fall and winter months. 1924—Cotton. Three-Year Rotation. 1921-—O0tton. 1922—Corn, wide rows, clean cultivate until harvesting; harvest early, plow under stubble deep, keep clean fallow, plant wheat or oats in the fall. 1923—Wheat or oats harvested, stubble worked in deep, kept clean fallow in summer, fall, and winter months. 1924-—C’otton; use 100 to 300 pounds of cotton seed meal per acre, plant in wide rows, clean cultivate until the last picking, then destroy the cotton plants; follow by clean fallow during fall and winter months. Three-Year Rotation with Legumes. 1921——Ootton. . 1922—Corn as above, followed by clean fallow and wheat or oats in the fall. 1923~—Wheat or oats harvested, stubble worked in and if season is favorable, that is, if moisture is plentiful in the soil, the land should be planted to guar, a hardy, resistant legume. In the fall, this legume should be plowed under, followed by clean fallow in the winter. 1924—Cott0n. _ '94 BULLETIN N0. 307. Four-Year Rotation with Legumes. 1921—O'otton. 1922—Corn, followed by clean fallow after harvesting and planted to wheat or oats in the fall. . 1923—~Wheat or oats harvested, stubble worked in and if season is favorable, followed by guar, in the fall the legume is worked under, followed by clean fallow during fall and winter months. 1924—Corn, wide rows, clean culture until harvesting, harvest early, plow under stubble, keep clean fallow during fall and winter months. In place of corn, grain sorghums may be used. 1925——Uotton. Four-Year Rotation. 1921—Ootton, followed by wheat or oats in the fall. . 1922—Wheat or oats harvested, stubble worked in, and if season is- favorable, follow by guar, clean cultivate, in the fall plow under guar as cover crop, clean fallow during fall and winter months. 1923-—Corn, wide rows, clean cultivate until harvesting, harvest early, plow under stubble, keep clean fallow, and harvest early, in the fall plant to wheat or oats. 1924—Wheat or oats harvested, stubble worked in and clean fallow" maintained during summer, fall and winter months. 1925—Ootton. Five-Year Rotation. 1921—C'otton, followed by wheat or oats in the fall. 1922——Wheat or oats harvested, stubble worked in deep and if season is favorable, follow by guar, the latter to be worked in as a cover crop, clean fallow during the fall and winter months. 1923———Corn, wide rows, clean culture until harvesting, harvest early, work under stubble, and in fall plant wheat or oats. i 1924-—Wheat or oats harvested, stubble worked in, if season is favor- able follow by feterita or guar in the fall, keep clean fallow during fall and winter months. 1925-——Corn, wide rows, clean cultivate until harvesting, harvest early, plow under stubble, keep clean fallow during fall and winter months. ' 1926—Cotton. Five-Year Rotation. 1921—Ootton, clean fallow during fall and winter months. 1922—Corn, Wide rows, clean cultivate until harvesting, harvest early,. plow under stubble and in fall plant wheat or oats. 1923—Wheat or oats harvested, stubble worked in, followed by feterita» or guar, clean fallow during fall and winter months. 1924—Corn, wide rows, clean cultivate until harvesting, harvest early, plow under stubble, and in fall plant wheat or oats. 1925—Wheat or oats harvested, stubble worked in and if season is favorable follow by feterita or guar, keep clean fallow during fall and winter months. 1926—Cotton. ‘aim... M- m“ TEXAS Roor Ror. 95 Five-Year Rotation. 1921—O0tt0n, followed by wheat or oats in the fall. 1922—Wheat or oats harvested, if season is favorable follow by guar or feterita, stubble worked in and clean fallow during fall and winter months. ' 1923—Corn, wide rows, clean cultivate until harvested, harvest early, p plow under stubble deep, keep clean fallow in fall and winter. 1924-——C0wpeas, planted early in drills, cultivate clean, harvest seed, plow under vines and follow by wheat or oats in the fall. 1925—Wheat or oats harvested, if season is favorable follow by feterita, work in stubble in the fall, keep clean fallow during fall and Winter months. 1926——C0tt0n. It is thus seen from the above described tentative systems of rota- tion that there is no hard and fast rule that‘ can be laid down as to the kinds to use. The thing to remember is that the first step in con- trolling the disease is to eradicate it from the land, if necessary, using a drastic system of cultivation and even a one-year fallow, and then todetermine on the method of rotation best suited to the particular locality and systematically and persistently carry out the clean culture idea so as to eliminate all susceptible carriers, especially weeds, during the years when the non-susceptible crops are grown. In this way, the land is freed from disease for the cotton crop. It is further seen that we are greatly handicapped in the use of legumes as cover crops. Inasmuch as the cowpea is a very susceptible host, it cannot always be recommended except perhaps in the five-year rotation indicated on this page. However, it is fortunate that the guar, a legume introduced by the Division of Agronomy of the Texas Agricultural Experiment Station, has proved highly resistant to Texas root rot. Furthermore, because of its being an annual, it may be used to advantage as a cover crop and adapted to any one desirable system of rotation after the land has been freed from the disease. In the extreme southern parts of Texas where irrigation is depended upon in making a crop, and where root rot is prevalent, it is somewhat more difficult to plan a rotation system. Here, then, the grower should aim first at freeing his land from the root rot fungus. This he could do by growing for two or three years resistant truck crops such as cabbage, onions, lettuce, cucurbits, following a rigid system of clean culture, and then by devoting the land to alfalfa for three or four years. Furthermore, all susceptible, perennial weeds, shrubs, and trees on roads or hedges should be kept down so as to prevent the possible re- infection of the lands so treated and freed from the pest. FUTURE WORK REQUIRING A SOLUTION. 1. A careful survey of the exact distribution and hosts affected by Texas root rot in counties where it was reported to occur. 2. To determine if Texas root rot is definitely confined to the heavy lands only. 96 BULLETIN N0. 307. 3. Why does Texas root rot apparently avoid all light sandy loam soils? - 4. To determine the possible reasons why Texas root rot has not gained a foothold in Mississippi, Alabama, and other Southern States where soil and climatic conditions are similar to that of Texas. 5. To determine the rate of summer spread of a root rot spot under wet and dry. seasons, and with various susceptible crops. 6. How is Texas root rot spread from field to field, and in new localities? 7. Further studies on the range of economic crops or weeds which are susceptible to the disease. 8. Field conditions best suited for infection. 9. How does the causal organism penetrate its host during infec- tion? 10. Extended studies in life history of the Texas root rot as it affects susceptible perennials, shrubs, and trees. 11. Extensive studies on the pathological morphology and physiol- ogy of the affected host. 12. More extended studies on the morphology and physiology of Phymatotrichum omnivorum on the host and in pure culture. ' 13. What are the field and laboratory conditions which favor or inhibit the production of conidia. , 14. Work out methods in germination of the conidia of Phyma- totrichum omnivorum. 15. Determine the function of these conidia. - Are they a factor in introducing the causal organism into new fields or localities? Are they short-lived, or long-lived? Can they live over winter as dormant spores? 16. Further extended studies on the probability of the conidia being carried about with the seed of susceptible hosts. 17. Intensive studies on the discovery of possible other spore stages (sexual or ascospores) of Phymatotrichum omnivorum either in the field or in pure culture. 18. Does P. omnivor-um live over winter in the soil as a dormant spore form? If so, determine the length of time in which these spores will retain their viability. 19. Intensive studies in clean culture methods, and developing practical means of destroying perennial weed carriers. 20. Further studies on the possible use of fertilizers, sulphur, or chemical soil disinfectants in controlling Texas root rot in the orchards or with perennial ornamentals. 2,1. Can root rot be controlled by destroying all vegetation in an infected spot when it first appears? ' \ 22. Intensive studies of the root system of susceptible hosts as in- fiuenced by soil fertility, climate, rainfall, or irrigation. TEXAS Rootr RoT. 97 REFERENCES. (1) Atkinson, G. F. Methods of obtaining pure cultures of Pam- mel’s fungus (of Texas root rot of cotton. Bot. Gaz. 18:16-19, 1893. (2) Chambers, C. O. Report of the Botany Department. 28th Annual Report, Okla. Agr. Expt. Sta. :34, 1919. (3) Curtis, G. W. Alfalfa root rot. Texas Agricultural Experi- ment Station, Bulletin No. 221211-215, 1892. (4) Duggar, B. M. Fungous diseases of plants, 2479-481, 1909. (5) Duggar, B. M. The Texas root rot fungus and its conidial stage. Ann. Mo. Bot. Gard. 3:11-23, 1916. (6) Elliot, J. A. Arkansas cotton diseases. Ark. Agr. Expt. Sta. Bul. 173.11, 1921. ('7) Galloway, B. T., and Woods, A. F. Root diseases. U. S. Dept. of Agr. Yearbook :248-249, 1896. . (8) Gilbert, W. W. Cotton diseases and their control. U. S. Dept. of Agr., Farmers’ Bulletin 11873-32, 1921., (9) Heald, F. D. Symptoms of diseases of plants. University of ‘Texas Bul. 135 z57-58, 1909. (10) Heald, F. D. Texas root rot of cotton. Texas Department of Agriculture, Bulletin No. 22:303-308, 1911. (11) Heald, F. D., and Wolf, F. A. A list of parasitic bacteria and fungi occurring in Texas. 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Twenty-eighth An- nual Report Ariz. Agr. Expt. tation, :431, 1917. (30) Tourney, J. W. Alfalfa root rot. Ninth Annual Report Ariz. Agr. Expt. Sta., :161-163, 1898. (31) Tyler, A. A. Alfalfa root rot. Eleventh Annual Report Ariz. Agr. Expt. Sta., :168-169, 1920. (32) Winter. Die Pilze, Vol. 1:405. (33) Wulf, Holuby. Zur Kryptogamen Flora von m. s. Podhrad Oest. Bot. Zeitung, 1874.’ (34) Youngblood, B. Suggested cropping systems for the black lands of Texas. U. S. Dept. of Agr., Bur. Pl. Ind., Circular No. 843-21, 1911.