UNIVERSITY OF CALIFORNIA Agricultural Experiment Station BENJ. IDE WHEELER, President COLLEGE OF AGRICULTURE TH omas forsyth hunt, dean and doctor ___!-_. _ v H E. VAN NORMAN, Vie E- Dl R ECTOR DbnfXLLbT and Dean University Farm School CIRCULAR No. 131 (June, 1915) SPRAYING FOR THE CONTROL OF THE WALNUT APHIS* By A. E. TYLOR DISTRIBUTION The European walnut aphis (Chromaphis juglandicola) is said to occur in all parts of the world where the English or Persian walnut tree is grown. In California it has been found in all the walnut sections and even on a few isolated trees in the Sierra Madre Moun- tains, many miles from any commercial orchards. INJURY During certain years, such as the season of 1914, the walnut trees may develop and mature their crop of good sized, clean nuts with no apparent injury resulting from the walnut aphis. Due to their rela- tively small number and their habit of feeding only on the under side of the foliage, the aphides are not observed in some seasons by many of the walnut growers. In other years, however, such as the season of 1913 and the two preceding seasons, when climatic conditions are especially favorable for their development the aphis may become so numerous in a comparatively short time as to become an important factor in the quality of the nut crop harvested. The honeydew given off by these insects falls on to the upper surfaces of fruit and foliage below and becomes a medium for the growth of the sooty mold fungus, so that in years of severe infestation both nuts and leaves become coated with a black, sticky material. The size of the nuts may be considerably reduced and a large percentage of the crop consists of small-sized, low-priced nuts. The fact that ' ' perforations, ' ' a term applied to nuts with a defectively formed shell, are also numerous during the years when the aphis infestation is severe has also been noticed by many growers. Whether or not the loss of plant juices and consequent drain upon the tree by the aphis is the actual cause of "perforation" has not, however, been proven. * Paper No. 4, Citrus Experiment Station, College of Agriculture, University of California, Riverside, California. LIFE HISTORY The following studies were carried on in the Whittier section of Southern California: 1 Stem Mothers. — During the spring, about the time the walnut trees are coming into leaf, the aphis eggs, which were deposited on the bark of branches or twigs during the preceding fall, hatch into young aphides or stem mothers. In the San Jose section, Mr. Davidson reports finding these stem mothers emerging from the egg on the early varieties of walnuts as early as February 15. During the spring of 1914, the first aphides seen in the Whittier and contiguous sections were found at La Habra in the first week of April, when the early varieties and seedling walnut trees were fairly well in leaf. The stem mothers produce viviparously the winged females, which in turn produce living young. It is this form of the aphis which increases in numbers during the spring, and, by July or late summer, may heavily infest the under side of the walnut foliage. In one severely infested orchard near the coast 200 aphides were counted on a single medium-sized leaflet on July 16, 1914, a year in which the infestation did not become severe except in a few instances. Number of Moults. — During the process of development the nymphs moult four times. In July and September, at least, the first moult occurs usually in from four to six days after birth ; the second in six to eight days; the third in eight to ten, or, in rare cases, in twelve days; the fourth and last moult occurs in from eleven to fourteen days from birth. Time of Development. — From the fourth or last moult the nymph emerges as a winged adult female. The number of days passed from birth to maturity during July, 1914, in the Whittier section varied from eleven to fourteen days, the greatest number of individuals maturing in twelve days. The length of time required to reach maturity may vary in dif- ferent sections, probably depending upon the climatic conditions. Davidson found during the month of July, 1911, at San Jose, that this time varied from fourteen to nineteen days, the majority maturing in sixteen days. i The life history of this and closely related species of walnut aphides has been studied in detail by Mr. W. M. Davidson in the San Jose section of California and published in Bulletin 100, Bur. Ent., U. S. D. A. Number of Young Produced. — During July, 1914, many aphides were placed in leaf cages and the number of offspring from each adult noted. The average number of young produced per adult female was 41, the largest number of young produced by any one adult being 59. During September and October similar records were obtained and at this time the average number of offspring from one adult was 37, and in one case an adult produced 46 young. The adults lived from thirty to thirty-five days and produced young almost up to the time of their death. The number of generations per year of the walnut aphis has not been definitely determined for Southern California. In the San Jose section there are ten and possibly eleven. Aphides may be found on the foliage until the latter drops in the winter. The number of pos- sible progeny resulting from a single stem mother during the season, therefore (estimating 35 young per female and ten generations), would be about 78,000,000,000,000. Oviparous Form. — During the late summer and fall the oviparous form or egg-laying stage of the walnut aphis appears. The female of this form differs in appearance from the winged viviparous adults, principally in being wingless and having two lateral black bands on the back. They do not form a distinct generation, but from July to and including the fall and until the leaves drop in the winter a portion of the young aphides may develop into the oviparous form, the wing- less female, and also the winged male. This is the egg-laying stage of the walnut aphis, and after fertilization the female goes to the twigs or branches, where the eggs are deposited in old leaf scars, in crotches, or on the bare surface of the bark. In the egg stage the aphis winters over on the old twigs, branches, or trunk, and in the spring, with the leafing out of the trees the eggs hatch, producing the stem mothers, and the life cycle is completed. WINTER CONTROL OF WALNUT APHIS During February and March of 1913. and again in 1914, Professor R. E. Smith and his associates carried on spraying experiments in Ventura and Santa Barbara counties for the control of the walnut blight and incidentally for the winter control of the walnut aphis. 2 Power outfits and the M. A. C. nozzles were used. By maintaining at least 200 pounds pressure they were able to spray thoroughly the highest trees from the ground with these nozzles. 2 See Circular 107, Univ. of Cal. Agr. Exp. Sta. The following spray was found very ' effective in destroying the aphis eggs on trunk, limb, and branch when these were thoroughly covered with the solution: Commercial lime-sulfur 5 gals. Quicklime 25 lbs. Water 95 gals. Twenty-five gallons of spray were applied to average sized trees ten years of age. This cost 45 cents per tree. For very large trees 40 gallons per tree were applied, costing 72 cents per tree. This includes total expense of materials and application. RESULTS OF WINTER SPRAYING IN 19143 During the second season of winter spraying with lime-sulphur the work which cost 45 cents per tree in 1913 was accomplished for 30 cents per tree, by reason of greater efficiency and improved methods. As to the results of the work, it may be said that both in 1913 and 1914 aphides were well controlled by the winter spray and only developed upon the sprayed trees by blowing in from the outside later in the season. The results of aphis control were markedly different upon trees which received abundant irrigation and those which had no irrigation. Upon well irrigated trees the effects of the spraying were not very pronounced, even when the insect became abundant upon unsprayed trees of the same kind. Upon unirrigated orchards, however, and especially during the dry season of 1913, very decided benefit could be seen from the spraying. This benefit showed itself by increased growth of the trees over those unsprayed and holding of the foliage later in the season. The latter was especially marked after the extremely hot, dry wind of September, 1913, which almost defoliated the unsprayed trees which had been heavily attacked by aphis, while the sprayed trees still retained much green foliage. In regard to the crop, no decided effect in quantity was seen during the season of spraying, but the effect upon quality was quite marked, the percentage of culls being decidedly less upon the sprayed trees. During the second season after spraying and aphis control, the crop of the sprayed trees increased decid- edly in quantity, the gain being due apparently to increased growth during the year of the spraying. The following table gives three years' records of this orchard: Crop Record, Robert Main Ranch, Goleta, 1912 Plot 1 No. trees 258 Good nuts, lbs. 3690 Good nuts per tree, lbs. 14.3 Culls, lbs. 767 Per cent culls 17 Spray None 2 227 3381 15.0 535 13y 2 None 3 165 1509 9.15 203 12 None 3 This discussion on the results of winter spraying in 1914 has been prepared by Professor R. E. Smith of the Division of Plant Pathology and has been intro- duced here to supplement data published in Circular 107 of this Station. Fig. 1. — Spraying walnut trees for the control of the walnut aphis. M. A. C. nozzle adjusted for spraying the lower half of the tree. Crop Record, Robert Main Ranch, Goleta, 1913 'lot 1 No. trees 258 Good nuts, lbs. 7250 Good nuts per tree, lbs. 28.0 Culls, lbs. 1739 Per cent culls 19 Spray None 2 227 6773 30.0 1179 15 None 3 165 2516 15.25 268 9% Lime-sulphur Crop Record, Robert Main Ranch, Goleta, 1914 Plot 1 No. trees 258 Good nuts, lbs. 6835 Good nuts per tree, lbs. 26.5 -I Culls, Per cent lbs. culls Very few culls this Spray r Lime-sulphur 2 227 7005 30.0 year Crop ran: 18.7% Jumbo «- 77.05 No. 1 4.25 No. 2 Lime-sulphur 3 165 5190 31.5 , Lime-sulphur This twenty-acre orchard was divided into three plots and the crop record of 1912, the year before spraying commenced, was obtained in order to get an idea of the average run of the orchard. The crop of that year, however, was only about half of the average in quantity. The trees in the plot chosen for spraying, No. 3, were below the others in size, the poorest part of the orchard being purposely taken. In March, 1913, Plot 3 was sprayed with lime-sulphur; the other two plots remained unsprayed. The new growth was coming out somewhat when Plot 3 was sprayed and received some injury from the appli- cation. This possibly accounts for the fact that the increase in crop over 1912, as shown in the column headed ' ' Good nuts per tree, ' ' was somewhat less in this plot than in numbers 1 and 2, the increase of the latter being about 100 per cent, while in Plot 3 it is about 70 per cent. In the column entitled "Percentage of culls" the effect of the spraying on the quality of the crop will be seen, this percentage in the unsprayed plots 1 and 2 increasing somewhat over 1912 on account of the hot wind in September, while in Plot 3 the percentage of culls was materially decreased in spite of the wind. In March, 1914, the whole orchard was sprayed with lime-sulphur, but again it will be seen by comparing the crops of plots 1 and 2 in that year with those of the previous season that no increase in the quantity of the crop was obtained from the spraying during the same season. The 1914 crop of Plot 3 shows plainly, how- ever, the effect of the spraying in 1913. These trees originally averaged little more than half the crop of those in plots 1 and 2, but they have now increased to an extent which gives them the heaviest production of the whole orchard. It appears from the figures that the crop of this plot has been about doubled as a result of the spraying. This we attribute to the increased growth of the trees resultant upon the control of aphis in this unirrigated orchard during the dry season of 1913. , I Fig. 2. — Spraying walnut trees for the control of the walnut aphis. M. A. C. nozzles adjusted for spraying the upper part of the tree. SUMMER SPRAYING FOR THE WALNUT APHIS There are two chief objections to winter spraying for the control of walnut aphis. (1) During many seasons the aphis does not become so numerous as to cause any economic or appreciable injury to fruit or trees. It is only in certain years that this insect becomes so serious a pest as to require control measures. In order to check the injury from the aphis during these epidemic years with the winter spraying, however, it is necessary to spray every year, since the seasons of severe infes- tation cannot be forecasted. (2) The walnut aphis spreads rapidly by migration, so that for best results to continue throughout the season from the winter spraying large blocks or entire sections must be sprayed during the dormant period. For these reasons it was deemed advisable to determine the effect of summer spraying. During the season of 1914 the aphides did not become so numerous in most sections of Southern California as to cause any serious injury, so that the actual cash benefit to the grower resulting from such spraying could not be estimated. It has been possible, however, to determine the practicability of such spraying, the comparative killing efficiency, the cost of the several sprays tried, and the possible injury to foliage resulting from the use of these sprays. Equipment. — The machine used for this work was a gasoline power outfit containing a 200-gallon tank and a pressure of 200 pounds was maintained. Two 50-foot lines of half-inch hose and the M. A. C. spraying nozzles were used. The ordinary nozzle of the cyclone type was also tried, but for this work proved unsatisfactory. With the M. A. C. nozzles the foliage of the largest trees may be effectively covered. In both the El Monte and Anaheim groves, where the experiments were conducted, the trees are ten years old and average 25 to 30 feet in height. In each experiment an average of six trees were thoroughly sprayed with 200 gallons of solution, or an average of 33 y 3 gallons of spray used per tree. When both the M. A. C. nozzles were working properly and a pressure of upwards of 200 pounds maintained the 200-gallon tank was emptied in from twenty-five to thirty minutes. With the refilling hose, practically ten minutes were consumed in refilling the tank. The time required to drive from the source of water to the place of work was not considered and may vary in every grove. In the spraying of large orchards, a supply wagon and extra man to mix and haul the spray from the source of water to the spray machine in the field should be part of the equipment. Results. — The following is a summary account of results obtained from the several sprays tried in the Killian and Neff orchards. One tank of 200 gallons of each spray was used and from five to seven trees covered in each experiment. Two rows, one on the east and the other on the west side of the sprayed rows, were left unsprayed and used as checks. There were fewer aphides on the east than on the west side. The results from each experiment, as well as in the two check rows, were obtained by counting the number of live aphides on thirty to sixty terminal leaflets (five to ten leaflets per tree) . Table Summarizing the Work on J. E. Killian 's Grove, El Monte Date of spraying Materials used to 1914 200 gallons of water 7/27 Black leaf 40, 1 pt. Whale oil soap, 4 lbs. 7/24 Black leaf 40, 1 pt. Liquid soap, 1 gal. 7/25 Lime-sulfur (com.), 2 gals. Black leaf 40, 15 fluid oz. 7/25 Spraysect, 1 gal. Liquid soap, 1 gal. 7/27 Milled sulfur, 6 lbs. Black leaf 40, 15 fluid oz. 7/27 Whale oil soap, 12 lbs. 7/28 Distillate, 2 gals. Whale oil soap, 4 lbs. 7/28 Kerosene, 8 gals. Liquid soap, 2 gals. Cost of materials Date No. No. of for 200 examined of live leaflets gals, of 1914 aphides examined spray $1.80 7/29 7/29 7/29 7/29 7/29 7/29 7/29 7/29 14 1 77 78 106 23 30 50 35 35 25 35 30 35 2.06 1.83 2.00 .72 .36 Remarks ..o injury No injury Considerable burning of leaves No injury No injury No injury Slight spotting 1.56 No injury Note. — On 35 terminal leaflets of east check row, 122 live aphides; on 35 terminal leaflets of west check row, 474 live aphides. Table Summarizing Summer Spraying Experiments on J. B. Neff's Grove, Anaheim Cost of materials Date of Date No. No. of for 200 spraving Materials used to examined of live leaflets gals, of 1914 200 gallons cf water 1914 aphides examined of spray Remarks 7/31 Black leaf 40, 1 pt. Liquid soap, 1 gal. 8/1 60 $2.06 No injury 7/31 Black leaf 40, 1 pt. Whale oil soap, 4 lbs. 8/1 2 60 1.80 No injury 7/31 Spraysect, 1 gal. Liquid soap, 1 gal. 8/1 349 60 2.00 No injury 7/31 Whale oil soap, 12 lbs. 8/1 358 60 .72 No injury 7/31 Distillate, 2 gals. Whale oil soap, 4 lbs. 8/1 307 60 .36 Some spotting of foliage 7/31 Kerosene, 8 gals. Liquid soap, 1% gals. 8/1 310 60 -1.37 No injury Note. — Sixty terminal leaflets on north side contained 1 739 live aphides; 60 terminal leaf- lets on south side contained 2298 live aphides. F. O. B., San Francisco. Spraysect (prepa-red), $1.50 per gallon, 10 Trees that have been pruned and thinned out can be more thor- oughly and effectively sprayed than those that have never been pruned. In the former case the leaflets are larger and fully expanded, while the leaflets on unpruned trees are small, partly doubled up and very crowded. In years that promise to be seasons of severe infestation the spray- ing should not be delayed until the injury to fruit and foliage has been done, but should be done in the early summer, so as to prevent the heavy infestation and resultant injury. The best results obtained from the summer spraying were obtained from those sprays containing black leaf 40, and of those tried the one containing black leaf 40, 1 pint, and 4 pounds of whale oil soap is the one advised for use. SUMMABY Injury. — During certain years of heavy infestation the English walnut aphis may reduce considerably the size of the nuts and depre- ciate the quality. "Perforated" nuts may also be due to aphis injury. The drain upon the tree is heavy. Aphis infestation may also increase the dissemination of the walnut blight. Life History. — At the time of leafing out of the walnut trees in spring the walnut aphis' eggs hatch, producing the stem mothers. The winged viviparous stage may be found on the walnut leaves during late spring, summer, and until the foliage falls in the winter. During the summer in the Whittier sections each viviparous female produces on an average 41 nymphs. One female produced 59 nymphs. The nymph, in Southern California, requires about twelve days from birth to maturity and there are about ten generations a year. The sexual or egg-laying stage does not form any distinct gener- ation, but may be found more or less numerous from July to the time the leaves fall. After fertilization the sexual females leave the foliage and deposit their eggs in old leaf scars, in the crotches, or on the bark of twig, branch, or trunk. Winter Control. — The most effective spray for the winter control of the walnut aphis is that recommended in Circular 107 of this Experiment Station, consisting of commercial lime-sulfur, 5 gallons; unslaked lime, 25 pounds; water, 95 gallons, which costs about $2.55 per 200 gallons of spray. Spraying should be done before growth starts in the spring. An average of 25 gallons of spray is required for trees ten years old and 40 gallons for larger trees. Average cost of spraying for trees of 10 years 35 cents Average cost of spraying very large trees 75 cents 11 The chief drawbacks of winter spraying are (1) the necessity of spraying every year; (2) rapid migrations of aphis from surrounding unsprayed trees. Summer Control. — The most efficient spray found for control of walnut aphis during the summer contains black leaf 40, 1 pint ; whale oil soap, 4 pounds ; water, 200 gallons, and costs $1.80 per 200 gallons of spray, when the materials are purchased in small amounts. About 30 to 35 gallons of spray are required to thoroughly covt r ten-year-old walnut trees. The M. A. C. nozzles are the most suitalle ones found for spraying walnut trees. STATION PUBLICATIONS AVAILABLE FOR DISTRIBUTION REPORTS 1897. Resistant Vines, their Selection, Adaptation, and Grafting. Appendix to Viticultural Report for 1896. 1902. Report of the Agricultural Experiment Station for 1898-1901. 1903. Report of the Agricultural Experiment Station for 1901-03. 1904. Twenty-second Report of the Agricultural Experiment Station for 1903-04. 1914. Report of the College of Agriculture and the Agricultural Experiment Station, July, 1913-June, 1914. BULLETINS No. 168. Observations on Some Vine Diseases in Sonoma County. 169. Tolerance of the Sugar Beet for Alkali. Studies in Grasshopper Control. A New Wine-Cooling Machine. A New Method of Making Dry Red Wine. Mosquito Control. Analysis of Paris Green and Lead Arsenate. Proposed Insecticide Law. The California Tussock-Moth. 184. Report of the Plant Pathologist to July 1, 1906. 185. Report of Progress in Cereal Investi- gations. The California Grape Root-worm. Grape Culture in California; Improved Methods of Wine-making; Yeast from California Grapes. The Grape Leaf-Hopper. Report of the Plant Pathologist to July 1, 1909. 207. The Control of the Argentine Ant. 208. The Late Blight of Celerv. 211. How to Increase the Yield of Wheat in California. 212. California White Wheats. 170. 174. 177. 178. 182. 183. 195. 197. 198. 203. 213. 216. 220. 225. 227. 230. 234. 241. 242. 243. 244. 246. 248. 249. 250. 251. 252. 253. 254. 255. The Principles of Wine-making. A Progress Report . upon Soil and Climatic Factors Influencing the Composition of Wheat. Dosage Tables. Tolerance of Eucalyptus for Alkali. Grape Vinegar. Enological Investigations. Red Spiders and Mites of Citrus Trees. Vine Pruning in California. Part I. Humus in California Soils. The Intradermal Test for Tuberculosis in Cattle and Hogs. Utilization of Waste Oranges. Vine Pruning in California. Part II. The Economic Value of Pacific Coast Kelps. Stock Poisoning Plants of California. The Loquat. Utilization of the Nitrogen and Or- ganic Matter in Septic and Imhoff Tank Sludges. Deterioration of Lumber. Irrigation and Soil Conditions in the. Sierra Nevada Foothills, California. The Avocado in California. The Citricola Fcale. CIRCULARS No. No. 65. The California Insecticide Law. 109. 69. The Extermination of Morning-Glor \ 70. Observations on the Status of Corn Growing in California. 110. 76. Hot Room Callusing. 111. 79. List of Insecticide Dealers. 80. Bovs' and Girls' Clubs. 113. 82. The Common Ground Squirrels of 114. California. 115. 83. Potato Growing Clubs. 117. 87. Alfalfa. 88. Advantages to the Breeder in Testing 118. his Pure-bred Cows for the Register 119. of Merit. 121. 91. Disinfection on the Farm. 92. Infectious Abortion and Sterilitv in 122. Cows. 100. Pruning Frosted Citrus Trees. 123. 101. Codling Moth Control in the Pacra- mento Valley. 124. 106 r ; '-^ct'ons for using Anti-Hog-Cholera 125. Serum. 126. 107. Spraying Walnut Trees for Blight and 127. Aphis Control. 128. 1 08. Grape Juice. 129. 130. Community or Local Extension Work by the High School Agricultural De- partment. Green Manuring in California. The Use of Lime and Gypsum on Cali- fornia Soils. Correspondence Courses in Agriculture. Increasing the Dutv of Water. Grafting Vinifera Vineyards. The Selection and Cost of a Small Pumping Plant. The Countv Farm Bureau Winery Directions. Some Things the Prospective Settler Should Know. The Management of Strawberry Soils in Pajaro Vallev. Fundamental Principles of Co-opera- tion in Agriculture. Alfalfa Silage for Fattening Steers. Aphids on Grain and Cantaloupes. Spraying for the Grape Leaf Hopper. House Fumigation. Insecticide Formulas. The Control of Citrus Insects. Cabbage Growing in California.