UNIVERSITY OF CALIFORNIA PUBLICATIONS COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA BROWN ROT OF APRICOTS By W. L. HOWARD and W. T. HORNE DECIDUOUS FRUIT STATION, MOUNTAIN VIEW, SANTA CLARA COUNTY Offices, laboratory and garage partially concealed by the large pepper tree at the side of the residence. Established January 1, 1920. BULLETIN No. 326 UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1921 David P. Barrows, President of the University. EXPERIMENT STATION STAFF HEADS OF DIVISIONS Thomas Forsyth Hunt, Dean. Edward J. Wickson, Horticulture (Emeritus). Walter Mulford, Forestry, Director of Resident Instruction. C. M. Haring, Veterinary Science, Director Agricultural Experiment Station. B. H. Crocheron, Director of Agricultural Extension. Hubert E. Van Norman, Vice-Director; Dairy Management. James T. Barrett, Acting Director of Citrus Experiment Station; Plant Pathology William A. Setchell, Botany. Myer E. Jaffa, Nutrition. Ralph E. Smith, Plant Pathology. John W. Gilmore, Agronomy. Charles F. Shaw, Soil Technology. John W. Gregg, Landscape Gardening and Floriculture. Frederic T. Bioletti, Viticulture and Fruit Products. Warren T. Clarke, Agricultural Extension. John S. Burd, Agricultural Chemistry. Charles B. Lipman, Soil Chemistry and Bacteriology. Ernest B. Babcock, Genetics. Gordon H. True, Animal Husbandry. Fritz W. Woll, Animal Nutrition. W. P. Kelley, Agricultural Chemistry. H. J. Quayle, Entomology. Elwood Mead, Rural Institutions. H. S. Reed, Plant Physiology. L. D. Batchelor, Orchard Management. J. C. Whitten, Pomology. IFrank Adams, Irrigation Investigations. C. L. Roadhouse, Dairy Industry. R. L. Adams, Farm Management. F. L. Griffin, Agricultural Education. John E. Dougherty, Poultry Husbandry. W. B. Herms. Entomology and Parasitology. L. J. Fletcher, Agricultural Engineering. Edwin C. Voorhies, Assistant to the Dean. fin co-operation with office of Public Roads and Rural Engineering, U. S. Department of Agriculture. BROWN ROT OF APRICOTS By W. L. HOWARD and WM. T. HORNEi Brown rot is a fungus disease affecting apricots and various other stone fruit trees. 2 It attacks both the ripening fruit and the twigs; but since the attack on the ripening fruit is serious, it is to this attack that reference is made when speaking of the brown rot. In Califor- nia, however, the attack on the twigs has attracted more attention. In this the withering flowers become infected and not only the blossoms and young fruits are killed but also the twigs to a distance of several inches. Atmospheric moisture favors the growth of the fungus, which forms spores in gray pustules of about the size of a pin head on rotting fruit and on blighted flowers and twigs. In California it is practically confined to the regions exposed to ocean influences and does not develop except in times of unusually moist weather. On the basis of numerous experiments and observations as to the best way of treating this disease, the University of California has recommended a thorough cleaning out of all blighted twigs and rotted fruits of the preceding year, to be followed by a spray program consisting of two applications of winter strength lime-sulphur solution in quick succession just before blossoming and a third spray of summer strength lime-sulphur solution while the calyxes or jackets are still on the fruit. As this program seemed unduly burdensome, a new set of experi- ments was commenced by the University at the Deciduous Fruit Station at Mountain View, Santa Clara County. These experiments give hope of a simpler control method, and it seems advisable to make a progress report of the work. The experiments were started in February, 1920. Sixteen differ- ent spray treatments were tried, and the results for the one season were so pronounced as to justify the conclusion that apricot blossoms may be effectively protected from brown rot by spraying the trees i The work described in this bulletin was planned by the authors jointly, but was carried out by the senior author and this statement of the results was prepared by him. The plates were arranged by the junior author. 2 The fungus causing this disease is now generally known as Sclerotinia cinerea (Bon.) Wor., but is found in older works in this country under the names Scl. fructigena (Pers.) Schroet. and Monilia fructiaena Pers. 74 UNIVERSITY OF CALIFORNLY EXPERIMENT STATION once, shortly before they come into bloom, with either lime-snlphur or Bordeaux mixture. The lime-sulphur should be used at the rate of 1 gallon to 9 gallons of water, and the Bordeaux mixture at a strength of 4—5-50 (4 pounds bluestone, 5 pounds fresh stone lime, 50 gallons water). Apparently the so-called dry lime-sulphur, used at the rate of 12 pounds to 50 gallons of water, is quite as effective as either of the other two sprays mentioned. The period of effective spraying is short. In the experiment, the best results followed spraying when the buds were considerably swollen. However, the protection against the disease was excellent when spraying was done at the time the trees were coming into bloom. Apparently there is no injury to the flowers if the spraying is done after they are fully open. The experiments showed conclusively that spraying after the trees have begun to go out of bloom is too late to be of much value. The disease apparently attacks the flowers after they are fully open. Spraying after the blooming period therefore is too late, as infection has already taken place. As with treatments for most diseases, spraying against the brown rot is a preventive rather than a cure. No evidence has been secured to show that spraying apricot trees before the buds begin to swell affords any protection against the disease. It may be assumed therefore that early winter spraying against the brown rot is useless. Normally, apricot trees in the Santa Clara Valley come into bloom in from seven to ten days after the buds are swollen sufficiently to show the white lines where the bud scales have expanded to accommo- date the growth. In regions near the ocean, such as the Pajaro Valley, in Santa Cruz County, and the Aromas district, in Monterey County, the blooming season may be very irregular. During the season of 1920 many orchards had a blooming period lasting from two to four weeks. Under such circumstances, when the first flowers begin to open on any given tree, a majority of the buds will probably show little or no signs of growth. The best recommendation that can be made for meeting these conditions is to commence the spraying when the first considerable number of flowers are opening. While a spray at this time might not afford the fullest protection to the latest buds, it would undoubtedly protect a great majority in their different stages of development. To delay the spraying until the most forward flowers have passed out of bloom simply invites infection, while spraying as the forward ones are coming out of bloom completely protects those that are fully open, and, in greater or less degree, also protects those that are not yet open. Bulletin 326 BROWN ROT OF APRICOTS 75 Fig. 1. — Severe case of brown rot twig blight on apricot tree showing many dead twigs and shoots. Photographed by Miss E. H. Phillips, April 23, 1917. 76 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION THE SPRAYING EXPERIMENTS Since the brown rot does its chief harm by attacking the apricot trees when in bloom, killing not only the blossoms but the entire fruit spurs as well, a spraying experiment was planned to find what mater- ials would protect the flowers from infection, and at what time or times they should be applied. Experiments carried on in previous years by the Division of Plant Pathology of the University of Cali- fornia indicated that lime-sulphur might be a good fungicide for the purpose if three sprayings were given, beginning when the buds were swelling and ending as the trees were going out of bloom. Taking this information as a starting point in the experiment begin- ning in February, 1920, the trees were sprayed at three stages of development, namely: when the buds were swelling, when the buds were opening, and when the flowers were falling. The test included the following materials : lime-sulphur, Bordeaux mixture, crude oil emulsion, distillate emulsion, dry lime-sulphur, dry sulphur (as a dust spray), and lime whitewash. The lime-sulphur was used at the standard winter strength of 1 gallon to 9 gallons of water when used as a dormant spray, 3 and 1 gallon to 29 gallons of water when used as a summer spray. In one test the lime-sulphur was used at half strength. The Bordeaux mixture was used at a strength of 4-5-50 (4 pounds copper sulphate, 5 pounds fresh lump lime, 50 gallons water) and also at a strength of 1 3^-2^2-50, both being dormant sprays. Crude oil emulsion was used at the rate of 15-100 (15 gallons of the emulsion and water to make 100 gallons) ; this was a dormant spray. The distillate emulsion was used at a strength of 15-200 (15 gallons of the emulsion and water to make 200 gallons). The dry lime-sulphur was used at the rate of 12 pounds to 50 gallons of water as a dormant spray, and 21/2 pounds to 50 gallons as a summer spray. The lime whitewash was made by the following formula : lime 10 pounds, sulphur 2 pounds, salt y 2 pound, the salt and sulphur being stirred in while the lime was slaking. Water was added until the proper consistency for spraying was attained. The dry sulphur was a brand known as "ventilated" sulphur, which is perhaps the best grade for dusting purposes. The applications given during the first two stages (when buds were swelling, and when buds were opening) were regarded as dor- 3 Spray applied as first blossoms were opening was classed as a dormant spray, since spray of winter strength caused no injury at this stage, i.e., before the leaves were out. Bulletin 326 BROWN ROT OF APRICOTS 77 mant sprays and the materials were used at winter -strength. At the third stage (when flowers were falling) the trees were looked upon as being in a growing condition, as the leaf buds were then about to open, so the sprays were diluted to summer strength. In addition to the single sprayings given at the three stages mentioned, certain rows were sprayed three times, that is, at all three of the different stages. When three sprayings were given, the first two, as before stated, were at winter strength and the third at summer strength. All the apricots in the spraying experiment were of the Blenheim variety. The trees were about twenty years old, of fair vigor con- sidering the short rainfall of the winters of 1919 and 1920, and had been bearing average crops. They did not show much indication of having suffered seriously from the brown rot in previous years. Almost up to the day when the first spraying was done, the weather had been too dry to favor the growth of the disease. When first sprayed, the buds had been showing signs of growth for several days; they were swollen so that the white streaks caused by the slipping of the bud scales were very noticeable. The rains began as the spraying started, and continued intermittently until several days after the last applications were made. The work was done with a barrel sprayer and a common Bordeaux nozzle. The pressure per- haps did not average much above 75 pounds, although at times it ran as high as 125 pounds. All parts of the trees were covered, from three to three and one-half gallons of material per tree being used. The results of the spraying are shown in the tables which follow : TABLE I Trees Sprayed as Buds were Swelling Spray treatment Spraying date Average no. diseased twigs per tree Efficiency of treatment, per cent Eow 3 Lime-sulphur 1-10 Feb. 17 6 92.3 Eow 4 Bordeaux mixture 4-5-50 Feb. 17 6 92.3 Eow 9 Crude oil emulsion 15-100 Feb. 21 15 80.7 Eow 10 Bordeaux mixture l%-2%-50 Feb. 21 9 88.4 Eow 16 Distillate emulsion 15-200 Feb. 23 94 —20.0 Eow 1 Unsprayed row 78 TABLE II Trees Sprayed as Buds i were Opening Spray treatment Spraying date Average no. diseased twigs per tree Efficiency of treatment, per cent Eow 5 Lime-sulphur 1-10 Feb. 28 7 90.4 Eow 7 Bordeaux mixture 4-5-50 Feb. 28 9 87.6 Eow 12 Dry lime-sulphur 12-50 Feb. 28 8 89.0 Eow 15 Unsprayed row 73 78 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE III Trees Sprayed as Flowers were Falling Average no. Spraying diseased twigs Spray treatment date per tree Lime-sulphur 1-30 March 10 39 Efficiency of treatment, per cent 55.6 Bordeaux mixture l%-2%-50 March 10 60 31.8 f March 2 | Sulphur dust \ and \ 47 [March 10 J 53.4 Lime whitewash March 17 128 —45.4 Eow 6 Bow 13 Bow 14 Bow 18 Bow 19 Unsprayed row* 88 * This row was later (May 25) sprayed with self -boiled lime-sulphur. This was long- after the brown rot had ceased to be active, so that, for statistical pur- poses, this may be regarded as an unsprayed row. TABLE IV Sprayed Three Times : As Buds were Swelling, As Buds were Opening, As Flowers were Falling Average no. Efficiency of Spraying diseased twigs treatment, Spray treatment date per tree per cent fFeb. 17 1 Bow 2 Lime-sulphur 1-10; 1-10; 1-30 <{ Feb. 28 \ 4 94.7 [March 10 J [Feb. 17 1 Bow 8 Lime-sulphur 1-10; 1-10; 1-30* ] Feb. 28 I 7 93.7 [March 10 J fFeb. 17 1 Bow 17 Lime-sulphur 1-20; 1-20; 1-60 ] Feb. 28 I 12 84.2 [March 10 J fFeb. 21 1 Bow 11 Dry lime-sulphur 12-50; 12-50; j Yeh. 28 I 13 82.8 21 /2-50 [March 10 J Bow 20 Unsprayed row 76 * Two different rows, widely separated in the orchard, were given the same lime-sulphur treatment. The figures show very clearly that the disease can be held in reasonable check by spraying, and that lime-sulphur and Bordeaux mixture at winter strength, when applied at the right time, are about equally effective. Each gave above 90 per cent control when used as a single spray. The figures also indicate that spraying as the trees are passing out of bloom is apparently too late and does very little good. It is true that the summer strength of lime-sulphur gave 55 per cent protection, but to be really efficient a spray should reduce disease infection by 75 per cent to 95 per cent. The figures do not show much difference in the effects of the spraying when buds were swelling and when buds were opening. This is fortunate, as most growers will be forced to begin their spraying four or five days before Bulletin 326 BROWN ROT OP APRICOTS 79 the buds begin to open in order to be able to finish by the time the trees are coming into bloom. Also there is always danger of delay caused by mishaps to equipment and by rain and wet ground. The crude oil emulsion mentioned under Table I was included, not because it was thought to be a fungicide, but in order to see if it would cause any spray injury when buds were much swollen. There was not a trace of spray injury, but this might be due to the fact that the spraying was done in rainy weather. There were several days of very cold, rainy, and cloudy weather about this time. Injury from oil sprays, which is now very rare, is believed to occur only when buds are quite dormant or very dry. There is seldom any injury when buds are beginning to be active. The surprise of this test was that the row sprayed with the oil emulsion showed very little brown rot. Although this material cannot yet be recommended as a brown rot spray, it is hoped that those who can will try it experimentally in a small way. If it should prove to be reliable for controlling the brown rot, it would indeed be a valuable spray, as it would at the same time rid the trees of the brown apricot scale, which at present must be sprayed against separately every two or three years. It is very apparent that the distillate emulsion is of no value as a spray against brown rot, and the lime whitewash spray appeared to be worse than useless. All the sprays under Table III, however, were applied too late to do much good; but even so, the whitewash made the poorest showing of all in that group. It is unfortunate that no trees were dusted with the "ventilated" sulphur in either of the first two stages of the buds. The so-called dry lime-sulphur made a good showing wherever it was tried, and apparently it is as reliable as either the common lime- sulphur or Bordeaux mixture for controlling the brown rot. Table IV, taken by itself, would seem to indicate that three spray- ings are very satisfactory for controlling the brown rot, but from Tables I, II, and III it is plain that one spraying, after the buds are well swollen and before the trees blossom, is entirely sufficient. It was this first or second spraying, then, or the combination of first, second, and possibly third, and not the third spraying alone that did the work. This is indeed fortunate, as growers who tried to spray their trees three times found such a program impracticable on account of the short period allowed for the work and the inevitable delays due to the weather. 80 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION OTHER RESULTS FROM SPRAYING All the trees in the experiment, both sprayed and unsprayed, had a full bloom and set a heavy crop of fruit. When the fruit was thinned, beginning April 19, it was noticed that trees sprayed with winter strength lime-sulphur or dry lime-sulphur were practically free from attack by the peach twig borer (Anarsia lineatella) , while those sprayed with Bordeaux and other materials or not sprayed at all were seriously infested. This insect is already present in many of Fig. 2. — Three Boyal Anne cherries inoculated with the brown rot fungus from blighted apricot twigs. The two fruits below were punctured with a sterile needle at the same time. Inoculated June 30. Photographed July 7, by Miss E. H. Phillips. the orchards that are badly infected by brown rot, and a lime-sulphur spray of dormant strength shortly before the trees come into bloom is the only reliable treatment known for holding it in check. It is fortunate that this same spray will also control the brown rot. If the peach worm or twig borer has not yet appeared in an orchard where brown rot is present, Bordeaux mixture is a reliable spray against the brown rot alone. Bulletin 326 BROWN ROT OF APRICOTS 81 DO SULPHUR SPRAYS CAUSE INJURY TO APRICOTS? There is a tradition in some apricot sections, and especially in the Santa Clara Valley, that lime-sulphur sprays may injure the fruit by causing it to be under-sized or late in ripening. In the spraying Fig. 3. — Blighted twigs of apricot, April 7, 1917. Gum shows near the lower end of the twigs. This is usually near the end of the killed area. Spore pustules usually show on twigs and dead flowers at this stage but are not clearly shown in this picture. When the twig is cut into it is found brown and dead. experiment described above, there was not a trace of injury observed from any of the sprays except the self-boiled lime-sulphur, which, at present, is not recommended for apricots at any time. Even where trees were sprayed three times with the commercial lime-sulphur, the 82 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION harvesting records showed no differences in time of ripening or in fruit sizes that were traceable to the spray treatments. Fortunately, the three spray program with the lime-sulphur was carried out in duplicate, the two rows being widely separated in the experiment plot. One of these rows had small fruit, but it was very apparent that this was due to the fact that the trees were subnormal in point of vigor. The other row receiving the same treatment consisted of normal trees, and the fruit at harvest time was found to be normal in every respect. One row (see footnote, Table III) was sprayed on May 25, after the fruit was nearly grown, with an 8-8-50 solution of self -boiled lime-sulphur. This material had a very marked effect on the fruit. Practically every apricot that was at least half covered with the spray ceased to develop. It was very apparent that this spray, which is in universal use for controlling brown rot in peaches in the eastern and southern states, cannot safely be used on apricots after the fruit has set. YIELD AND GRADES OF SPRAYED APRICOTS All the fruit in the experiment orchard ran small in size, owing to the inadequate supply of soil moisture early in the season. At the close of the winter rains the ground was wet down only about thirty inches. The orchard was irrigated May 15, the earliest date at which it was possible to procure water, and again June 15, but apparently the trees needed water early in order to make the proper growth and put size on the fruit. The experiment apricots were harvested in three pickings, that is, on July 12, 18, and 24. The fruit from each tree under the different treatments was separately weighed and graded at each picking. Only two grades were recog- nized, that which was acceptable to the cannery and that which was not. The cannery would accept no fruit smaller than fourteen to the pound; all fruit under this size had to be dried. For convenience these two grades are designated as No. 1 and No. 2. The results of the grading are summarized in Table V. Bulletin 326 BROWN ROT OF APRICOTS 83 TABLE V Average Yield per Tree and Percentage of Fruit of Cannery Grade and Below Cannery Grade Produced Under the Different Spray Treatments Av. yield per tree, Percentage Percentage Row Spray treatment lbs. No. 1 fruit No. 2 fruit 1 Unsprayed* 95.5 93.80 6.20 2 Three lime-sulphur sprays.... 50.5 3.33 96.67 3 Linie-sulphur once; as buds were swelling 46.0 22.82 77.18 4 Bordeaux once; as buds were swelling 51.16 65.94 34.06 5 Lime-sulphur once; as buds were open- ing 63.00 71.58 28.42 6 Lime-sulphur once; as flowers were falling 83.16 88.78 11.22 7 Bordeaux once; as buds were opening 104.83 51.51 48.49 7a Unsprayedf 102.72 76.86 23.13 8 Three lime-sulphur sprays 79.00 70.68 29.32 9 Ortho crude oil once; as buds were much swollen 103.00 84.96 15.04 10 Weak Bordeaux once; as buds were swelling 78.00 78.64 21.36 11 Three dry lime-sulphur sprays 92.5 26.53 73.47 12 Dry lime-sulphur once; as buds were opening 57.00 30.11 69.89 13 Weak Bordeaux once; as flowers were falling 89.83 43.42 56.58 14 Sulphur dust twice; as flowers were falling 176.13 72.25 27.75 15 Unsprayed 115.23 80.27 19.73 16 Distillate emulsion once; as buds were swelling 125.50 90.29 9.71 17 Three weak lime-sulphur sprays 77.83 22.92 77.08 18 Lime whitewash once; as flowers were falling 153.83 79.64 20.36 19 One application self-boiled lime-sul- phur, May 25 70.33 23.22 76.78 20 Unsprayed* 73.5 92.31 7.69 * Outside row. f This row was made up of the end tree of all sprayed rows. From the yield records shown in Table V it might be inferred that spraying does not protect the fruit sufficiently to increase the yield. This was true in the experiment under discussion, as the brown 84 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION rot was not bad enough in this orchard to affect the yield materially. Even though numerous flower clusters were destroyed and many fruiting spurs killed, the set of fruit on the healthy wood that remained was sufficient to make a full crop. Unfortunately, many of the trees were weak from inadequate irrigation in previous years and from a shortage in soil moisture in April and early May of this Fig. 4. — Apricot mummy remaining on the tree and producing fresh spore pustules the following spring. Pustules are seen with especial clearness near the stem. The spores are very small and a great number are formed on a single pustule and carried away by the wind. May 5, 1915. season, so that the fruit did not size properly. Also it was realized too late that many of the trees, particularly the weaker ones, were not thinned heavily enough. Owing to the light attack of the brown rot in the experiment orchard, the yield records must be studied not with a view to deter- mining whether the disease itself reduced the yield — for we know it did not — but to determine whether the sprays caused the fruit to Bulletin 326 BROWN ROT OF APRICOTS 85 be undersized or late in ripening. The fact has been well established (Tables I and II) that spraying will reduce the disease by more than 90 per cent, and there is every reason to believe that this rate of control will hold just as true when the disease infection is heavy as when it is light. Row I, unsprayed, was an outside row, and consequently con- tained better than average trees, yet there was considerable variation Fig. 5. — Brown rot cankers in almond branches from twig blight the previous spring. Pustules of new spores are forming on the old cankers. A mass of gum shows on the lower twig. April, 1920. in size and vigor, and the yield per tree varied from 40 to 149 pounds. Still, there was enough extra good fruit on the best trees to bring the yield of No. 1 apricots to 93.8 per cent, the highest of any row in the experiment. Incidentally, one of the trees in this row — the best one — ripened its fruit among the latest in the orchard. Row 2, sprayed three times with lime-sulphur, contained some very poor trees. They were somewhat undersized and appeared to have made but little growth in the past two years. They not only aver- aged smaller than those in Row 1, but were not so vigorous. This 86 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION was one of the rows that was not thinned enough. As a result, all the fruit was small. Row 2, however, was among the first in the orchard to be harvested. The fruit matured early because the trees were weak. Row 8 was also sprayed three times with lime-sulphur, but the trees were normal in size and vigor and they ripened their fruit along with other trees of comparable size and condition. This row was about equal in every way to Row 7, which was sprayed with Bordeaux. While the yield of Row 8 was not so great as that of Row 7, the per- centage of No. 1 fruit was much higher — 70.6 as compared with 51.5. There has been no question of injury to the fruit from Bordeaux mixture. Taking rows 4 and 7, both Bordeaux sprayed, it is seen that they show a decidedly lower percentage of No. 1 fruit than rows 5 and 6, sprayed with lime-sulphur. Rows 2 and 3 are excluded from the comparisons on account of too many weak trees. Observa- tion of the sprayed trees certainly showed no indication of injury from either the lime-sulphur or the Bordeaux mixture. EXPERIENCE OF GROWERS Numerous growers in the Santa Clara Valley, have sprayed apricots with lime-sulphur against brown rot. The experience of one of these, Joe Seitz, located two miles northwest of Mountain View near the State highway, is the most instructive. Mr. Seitz has sprayed his ten-acre orchard for four successive years as follows : in 1917, just before the trees came into bloom, with lime-sulphur 1-10 ; in 1918 the same ; in 1919 with lime-sulphur 1-30 just after the bloom ; and in 1920 twice before the bloom with 1-10 and once after with 1-30. He reports having always controlled the disease within reasonable limits, without causing injury to the fruit. He will continue to spray hereafter, but thinks that one application of lime-sulphur 1-10, before the bloom, is sufficient. An apricot orchard immediately adjoining that of Mr. Seitz has never been sprayed against brown rot, and has suffered very severely from the disease every year. Contrasted with the above is the case of D. C. Bache, of Hamilton Avenue, near Campbell, who reports having sprayed his apricots in the spring of 1920 as follows : One part of the orchard received lime- sulphur 1-12 and another part 1-14 as buds were much swollen but not showing pink, and again received the same solutions as trees were passing out of bloom. Still another part of the orchard was sprayed once with lime-sulphur 1-20, and a final part with 1-30, both as trees were passing out of bloom. He considers that all these sprays Bulletin 326 BROWN ROT OF APRICOTS 87 were very effective in controlling the brown rot, but thinks that all caused the fruit to be small and late in ripening, and that spraying before the bloom was more harmful than after the bloom. This orchard was examined, and the fruit certainly was small and late in ripening. From the appearance of the trees and the treatment they had received this season, the trouble could not be attributed to lack of moisture in the soil; but the history of the orchard for the past two seasons could not be obtained, as Mr. Bache had just purchased the ranch. Hereafter Mr. Bache will spray with Bordeaux mixture, as he does not consider the peach twig borer, which causes wormy apricots in so many orchards, a serious problem. Several other orchards have been noted by Mr. Bache as having small fruit this season. He attributed the cause to spraying with lime-sulphur, but on examination the trouble seemed clearly to have been caused by lack of moisture in the soil. In some instances the trouble seemed to date back to the treatment received during the previous season or during the past two years. CUTTING OUT DISEASED TWIGS Blighted twigs and mummied fruits that remain on the trees through the fall and winter give rise, in the spring, to a new crop of brown rot spores. These spores on twigs and mummies are the principal known sources of brown rot. Accordingly, some time before the buds swell, all mummies and all affected twigs should be cut out and burned. It would have been impractical to remove all affected twigs when the disease first broke out or while it was still active, owing to the difficulty or impossibility of telling where the diseased wood left off and the healthy wood began. If the diseased wood is not all removed, the labor of cutting out the twigs may be lost, or, on the other hand, unnecessary damage to the tree may result from heavy pruning to make certain all affected parts are removed. An experiment in cutting out the diseased twigs soon after the appearance of the disease was tried on the John Losse ranch in Santa Clara Valley. The trees were large and in a fine state of vigor. The tops were rather dense, but fruit spurs were numerous throughout. The attack of brown rot was severe, most of the twigs being affected. On March 24, after the disease had apparently ceased to be active, every affected twig on two trees was cut out. The injured area, however, extends farther along the interior of the twig than on the outside. Hence, although great care was taken — even to making 50 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION two or three cuts — observations made ten days later showed that the disease had continued to develop in from 40 to 50 per cent of the twigs. A second cutting* was necessary to rid the tree of all affected twigs, and even this was not completely successful. The object of removing the diseased twigs so early in the season was to determine whether such treatment would protect the ripe fruit from being attacked by the rot. Observations made at harvest time, however, showed as much rot in the trees where the twigs had been removed as where they had not. It appears therefore that fruit rot cannot be prevented by cutting out the diseased twigs, but twig blight, it is believed, can be as effectively and more easily controlled by removing them in the fall or winter as by cutting them out in the spring. It is believed to be worth while to remove all affected twigs when the regular pruning is done, in order to prevent the disease from being carried over the winter. At the same time every mummied fruit should be collected from the trees and from the ground, and both twigs and mummies destroyed by burning. Confusion with Peach Blight. — During the past year there has been some confusion between brown rot and the diseases caused by the peach blight fungus, Coryneum beyerinckii. The peach blight fungus is active during the wet weather of winter and spring. On apricots it causes winter killing of buds or bud blight, shot-hole disease on the early leaves, and small corky spots on young green fruit. Peach blight fungus causes serious losses in the interior valleys and foothills but is rarely serious in the coast districts, whereas brown rot is confined almost entirely to the coast regions. Treatment for peach blight fungus on peaches and apricots consists in spraying with winter strength lime-sulphur solution or Bordeaux mixture in Novem- ber or early December and again as the buds swell in the spring. Some growers have been giving the spray in November to apricots in the coast districts, but this is evidently unnecessary in nearly all cases near the coast. STATION PUBLICATIONS AVAILABLE FOE FREE DISTRIBUTION BULLETINS No. 185. 251. 253. 257. 261. 262. 263. 266. 267. 268. 270. 271. 272. 273. 274. 275. 276. 278. 279. 280. 282. 283. 285. 286. Report of Progress in Cereal Investiga- tions. Utilization of the Nitrogen and Organic Matter in Septic and Imhoff Tank Sludges. Irrigation and Soil Conditions in the Sierra Nevada Foothills, California. New Dosage Tables. Melaxuma of the Walnut, " Juglans regia." Citrus Diseases of Florida and Cuba Compared with Those of California. Size Grades for Ripe Olives. A Spotting of Citrus Fruits Due to the Action of Oil Liberated from the Rind. Experiments with Stocks for Citrus. Growing and Grafting Olive Seedlings. A Comparison of Annual Cropping, Bi- ennial Cropping, and Green Manures on the Yield of Wheat. Feeding Dairy Calves in California. Commercial Fertilizers. Preliminary Report on Kearney Vine- yard Experimental Drain. The Common Honey Bee as an Agent in Prune Polination. The Cultivation of Belladonna in Cali- fornia. The Pomegranate. Grain Sorghums. Irrigation of Rice in California. Irrigation of Alfalfa in the Sacramento Valley. Trials with California Silage Crops for Dairy Cows. The Olive Insects of California. The Milch Goat in California. Commercial Fertilizers. No. 288. 290. 298. 299. 300. 301. 302. 303. 304. 308. 309. I 310. 311. 312. 313. 316. 317. 318. 319. 320. 321. 322. 323. 324. 325. Potash from Tule and the Fertilizer Value of Certain Marsh Plants. The June Drop of Washington Navel Oranges. Seedless Raisin Grapes. The Use of Lumber on California Farms. Commercial Fertilizers. California State Dairy Cow Competition, 1916-18. Control of Ground Squirrels by the Fumigation Method. Grape Syrup. A Study on the Effects of Freezes on Citrus in California. _ I. Fumigation with Liquid Hydrocianic Acid. II. Physical and Chemical Pro- perties of Liquid Hydrocianic Acid. The Carob in California. II. Nutri- tive Value of the Carob Bean. Plum Pollination. Investigations with Milking Machines. Mariout Barley. Pruning Young Deciduous Fruit Trees. The Kaki or Oriental Persimmon. Selections of Stocks in Citrus Propagation. The Effects of Alkali on Citrus Trees. Caprifigs and Caprification. Control of the Coyote in California. Commercial Production of Grape Syrup. The Evaporation of Grapes. Heavy vs. Light Grain Feeding for Dairy Cows. Storage of Perishable Fruit at Freezing Temperatures. Rice Irrigation Measurements and Ex- periments in Sacramento Valley, 1914- 1919. CIRCULARS No. 70. Observations on the Status of Corn Growing in California. 76. Hot Room Callusing. 82. The Common Ground Squirrels of California . 113. Correspondence Courses in Agriculture. 114. Increasing the Duty of Water. 115. Grafting Vinifera Vineyards. 117. The Selection and Cost of a Small Pump- ing Plant. 124. Alfalfa Silage for Fattening Steers. 126. Spraying for the Grape Leaf Hopper. 127. House Fumigation. 128. Insecticide Formulas. 129. The Control of Citrus Insects. 130. Cabbage Growing in California. 131. Spraying for Control of Walnut Aphis. 135. Official Tests of Dairy Cows. 136. Melilotus Indica. 137. Wood Decay in Orchard Trees. 138. The Silo in California Agriculture. 139. The Generation of Hydrocyanic Acid G ^,s in Fumigation by Portable Machines. 140. The Practical Application of Improved Methods of Fermentation in California Wineries during 1913 and 1914. 143. Control of Grasshoppers in Imperial Valley. 144. Oidium or Powdery Mildew of the Vine. 148. "Lungworms". 152. Some Observations on the Bulk Handling of Grain in California. 153. Announcement of the California State Dairy Cow Competition, 1916-18. 154. Irrigation Practice in Growing Small Fruits in California. 155. Bovine Tuberculosis. No. 156. How to Operate an Incubator. 157. Control of the Pear Scab. 158. Home and Farm Canning. 159. Agriculture in the Imperial Valley. 160. Lettuce Growing in California. 164. Small Fruit Culture in California. 165. Fundamentals of Sugar Beet Culture under California Conditions. 167. Feeding Stuffs of Minor Importance. 168. Spraying for the Control of Wild Morning- Glory within the Fog Belt. 169. The 1918 Grain Crop. 170. Fertilizing California Soils for the 1918 Crop. 172. Wheat Culture. 173. The Construction of the Wood-Hoop Silo. 175. Progress Report on the Marketing and Distribution of Milk. 176. Hog Cholera Prevention and the Serum Treatment. 177. Grain Sorghums. 178. The Packing of Apples in California. 179. Factors of Importance in Producing Milk of Low Bacterial Count. 181. Control of the California Ground Squirrel. 182. Extending the Area of Irrigated Wheat in California for 1918. 183. Infectious Abortion in Cows. 184. A Flock of Sheep on the Farm. 185. Beekeeping for the Fruit-grower and Small Rancher or Amateur. 187. Utilizing the Sorghums. 188. Lambing Sheds. 189. Winter Forage Crops. 190. Agriculture Clubs in California. 191. Pruning the Seedless Grapes. CIRCULARS — Continued No. 193. A Study of Farm Labor in California. 198. Syrup from Sweet Sorghum. 201. Helpful Hints to Hog Raisers. 202. County Organization for Rural Fire Control. 203. Peat as a Manure Substitute. 204. Handbook of Plant Diseases and Pest Control. 205. Blackleg. 206. Jack Cheese. 207. Neufchatel Cheese. 208. Summary of the Annual Reports_of the Farm Advisors of California. 210. Suggestions to the Settler in California. 213. Evaporators for Prune Drying. 214. Seed Treatment for the Prevention of Cereal Smuts. No. 215. Feeding Dairy Cows in California. 217. Methods for Marketing Vegetables in California. 218. Advanced Registry Testing of Dairy Cows. 219. The Present Status of Alkali. 220. Unfermented Fruit Juices. 221. How California is Helping People Own Farms and Rural Homes. 222. Fundamental Principles of Co-operation in Agriculture. 223. The Pear Thrips. 224. Control of the Brown Apricot Scale and the Italian Pear Scale on Deciduous Fruit Trees. 225. Propagation of Vines. 226. Protection of Vineyards from Phyl- loxera.