4 vj ^^^"^^-^^ Issued January 9, 1911. u. s. dp:partment of agriculture, BUREAU OF ENTOMOLOGY— CIRCULAR No. 131. L. O. HOWARD. Entomologist and Chiel of Bureau. HOW TO CONTROL THE PEAR THRIPS. S. W. FOSTER AND P. J{. JONES, Agents and Experts. WASMIMGTON : GOVERNMENT PRINTING OFFICE ; 1911 G7859-'-Cir. 131-11 1 A 33 B UREA U OF ENTOMOLOG Y. L. O. Howard, Entomologist and Chief of Bureau. C. L. Maklatt, Assistant Entomologist and Acting Chief in Absence of Chief. R. S. Clifton, Executive Assistant. W. F. Tastet, Chief Clerk. F. H. Chittenden, in charge of truck crop and stored product insect investigations. A. D. Hopkins, in charge of forest insect investigations. W. D. Hunter, in charge of southern Jie Id crop insect investigations. F. M. Webster, in charge of cereal and forage insect investigations. A. L. QuAiNTANCE, in charge of deciduous fruit insect investigations. E. F. Phillips, in charge of bee culture. D. Al. Rogers, in charge of preventing spread of moths, field work. RoLLA P. Currie, in charge of editorial work. Mabel Colcord, librarian. Deciduous Fruit Insect Investigations. A. L. QuAiNTANCE, w charge. Fred. Johnson, S. W.. Foster, E. L. Jenne, P. R. Jones, A. G. Hammar, C. \V. Hooker, J. R. Horton, W. Postiff, J. B. Gill, agents and experts. E. W. Scott, J. F. Zimmer, entomological assistants. tCir. 131J (n) Circular No. 1 31 . Issued January 9, 1911. United States Department of Agriculture, BUREAU OF ENTOMOLOGY. L. O. HOWARD, Entomologist and Chief of Bureau. HOW TO CONTROL THE PEAR THRIPS.« (Euthrips pi/ri Daniel.) By S. W. P'osTER and P. R. Jones, Agents and Experts. DISTRIBUTION. The pear thrips (Euthrips pyri Daniel) (fig. 2) is at present confined to California and is very destructive throughout Santa Clara, Contra Costa, Solano, and Sacramento counties, with considerable areas infested in Alameda, Yolo, Napa, and Sonoma counties. (Fig. 1.) Re- ports of the presence of this species in other sec- tions of California and in Oregon have been re- ceived, but each case was closely investigated and the insect in question found to be some other species. Bagnal^ reports this insect in England; otherwise it is not known outside the State of California. ECONOMIC IMPORTANCE. Fig. 1.— Map showing area infested by pear thrips in California. (Original.) suddenness of attack in great numbers The pear thrips is at present tne most important in- sect pest with which the growers of de- ciduous fruits in the counties mentioned have to contend. On account of the minute size of the insect, the rapidity of its spread over large areas, and the completely blasting in a few « The present paper is an abstract of a more comprehensive report on the life history and control of the pear thrips to be published later. The recommendations given are based on the results of experiments carried out in the principal centers of infestation since the fall of 1908 to and including the summer of 1910. & Journal of Economic Biology, vol. 4, No. 2, 1909, 2 HOW TO CONTROL THE PEAR THKIPS. days all prospects for a crop of fruit — the control of this pest is a matter of considerable difficulty. As the insect is each year extending its range of food plants, its capabilities for dissemination are correspondingly increased. There is no reason to believe that the insect will disappear in a few years, but it should be regarded as a permanent pest and at once realized that only the most careful attention each 3"ear to necessary control measures will make it possible to continue the profitable culture of deciduous fruit in infested orchards. Conservative estimates place the damage caused by the pear thrips, in the Santa Clara Valley alone, during the j^ears from 1904 to 1910 at nearly $2,000,000, while the loss for the entire State during this period probably exceeds $3,500,000. It is safe to say that the thrips in the absence of treatment would cause an average yearly loss to the State of over $1,000,000. Also each additional year an increase of several hundred thousand dollars is to be expected, due to the increase of area infested and the greater losses in the areas previously infested. CHARACTER OF INJURY. Injury to the various fruit trees b}^ this species is caused b}" the feeding of the adults on the developing buds and early blossoms; by the deposition of eggs into the fruit stems, leaf stems, and newly formed fruit, and by the feeding of the larvae in the blossoms and on the young fruits and foliage. On pears the greater injury is pro- duced by the adults, which often prevent the trees from blooming, while on prunes and cherries the larvae frequently prevent a crop of fruit from setting after the trees have come into full bloom. Also, the deposition of eggs into the fruit stems of primes and cherries so weakens the stems that much of the young fruit falls. The feeding injury is not produced by a biting or chewing process. By rasping the tender surfaces in the developing fruit buds and the young fruits with their hardened or chitinous mouthparts, the thrips rupture the skin, causing an exudation of sap whicli is often followed by more or less fermentation, especially before blooming. The feeding by larvae on prunes after blooming causes the well-known thrips ^^scab," while most ()f the scarred and misshapen pears are caused by the work of the a(hdts. LIFE HISTORY. Adults. — The a(hdts (fig. 2) or winged form of the thrij)s first appear on the trees about tlie JiiidcUe of February and emergence HOW TO CONTROL THE PEAR THRIPS. 3 from the ground continues till early April, maximum emergence, however, occurring in late February and early March. Examina- FiG. 2.— The ppar thrips ( Euthrips pyrl): Adult, greatly enlarged. (Original.) tion of the tables of emergence records (Tables I to V) will show the dates of emergence for 1909-10: Table I. — Total daily emergence of thrips from all cages at laboratory, San Jose, Cal., J 909 and 19 W. Number Number . Number Number Date. thrips thrips Date thrips thrips emerging emerging emerging emerging in 1909. in 1910. in 1909. in 1910. Feb. 9 25 Mar. 8 219 275 10 18 9 776 144 11 16 10 497 100 12 16 11 498 73 13 4 12 338 179 14 88 13 313 45 15 18 22 14 248 20 16 27 15 279 7 17 52 34 16 259 4 18 192 33 17 152 20 19 192 14 18 42 7 20 169 23 19 61 2 21 75 62 20 28 2 22 23 24 25 26 27 28 Mar. 1 2 3 4 5 6 119 135 552 459 444 414 781 781 535 1,299 714 508 362 438 129 375 272 297 4.55 574 657 1,975 3,592 3,011 4,217 1,402 1,595 539 21 22 23 24 25 26 27 28 29 30 31 Apr. 1 2 3 2 6 13 3 2 3 7 7 2 3 1 1 1 4 HOW TO CONTROL THE PEAR THRIPS. Emergexce Record for Contra Costa County. Table II. — Emergence of thrips from cages placed in ground under trees in pear and prune orchards, Walnut Creek, Cal. 1909. 1910. Number Number Date. of thrips Date. of thrips i emerging. emergmg. 1 Feb. 13 Feb. 21 1 16 20 23 4 19 37 25 23 22 30 27 36 26 110 Mar. 1 56 Mar. 2 615 3 237 5 679 5 1,170 10 752 7 2,110 12 273 9 892 16 65 11 1,773 20 33 13 557 22 4 15 198 27 11 17 71 19 3 21 6 27 5 Table III. — Emergence of thrips from soil samples taken from orchard in November and December and kept in cages at laboratory, Walnut Creek, Cal. 1909. 1 1910. Number Number Date. of thrips Date. of thrips out. out. Feb. 12 3 Feb. 18 11 15 42 20 16 16 56 22 17 38 24 12 18 56 26 30 20 89 1 28 75 23 125 Mar. 2 377 25 185 4 918 27 246 « 937 Mar. 1 196 8 165 4 237 10 114 7 51 1 12 47 10 52 14 14 13 16 4 19 22 Emergence Record for Solano County, 1910. Table IV. — Emergence of thrips from cages placed in ground under trees in orchards Suisun. Cal. Number Number Date. of thrips Date. of thrips emerging. emerging. Fel). 17 3 Feb. 27 20 19 Mar. 1 47 21 3 121 23 10 484 25 ' 16 1 HOW TO CONTROL THE PEAR THRIPS. Table V. — Emergence of thrips from samples taken from orchard in November and Decem- ber and kept in cages at laboratory, Suisun, Cal. Number Number Date. of thrips Date. of thrips emerging. emergmg. Feb. 16 1 26 11 17 3 27 14 18 2 28 41 19 6 Mar. 1 105 20 1 2 247 21 1 3 243 22 4 7 612 23 2 12 357 24 5 16 82 25 11 19 8 Fig. 3.— The pear thrips: Eggs, high- ly magnified. (Original.) By the time the fruit buds have swollen sufficiently to separate the bud scales slightly at the tip the adults force their way within, feeding upon the tenderest portions inside the buds. When the thrips are present in sufficient numbers the buds are completely destroyed and the trees fail entirely to bloom. Eggs. — As soon as the first leaf surfaces or fruit stems are exposed egg laying usually begins, depending somewhat on the variety of fruit attacked. The first eggs are deposited the last days of February and oviposition continues till near the middle of April, being at its maximum, however, from the lOtli of March to the 1st of April. Most of the eggs (fig. 3) are deposited just under the epidermis in the fruit stems, young fruit, and leaf stems. The eggs require from five to seven- teen days to hatch, the average time being about eight days. Larvx. — By the time the trees are break- ing into full bloom the adults have done most of the damage caused by their feeding, and oviposition is at its height. Many of the earlier appearing adults are dying off and larvae (fig. 4) are beginning to appear in Larva, numbcrs. The very first larvae can usually be found about March 20, and are in maxi- mum numbers on the trees, feeding on the small fruit and young foliage, from the first to middle of April. Reaching their full devel- opment, the larvae drop from the trees, of their accord or with falling calyces, or are blown by wind or knocked off by rain. After the Fig. 4.— The pear thrips greatly enlarged. (Original.) HOW TO CONTROL THE PEAR THRIPS. middle of April the number on the trees diminishes rapidly, and by the last of April all the larvae are off the trees and in the ground. Here they work down into the first 3 or 4 inches of hard soil below the loose surface mulch and construct a tin}^ cell, where they remain until the following spring. Puyse. — The larvae mostly remain as such in these cells till Sep- tember, when pupation begins, pupae (fig. 5) being most abundant during October and November. Many adults can be found in the ground in December, and by the 1st of January practically all the thrips are in the adult stage and apparently ready to emerge and go into the trees whenever conditions are right. Broadly speaking, the thrips spend two months of the year in the adult, egg, and larval condition on the trees and the other ten months of the year as larvae, pupae, and adults in the ground. CONTROL MEASURES. The pear thrips is in some respects an unusual insect in that it remains in a dormant or semidormant condi- tion for about ten months of the year. Although on the trees for only two months out of the twelve, it is able in this short time, in the absence of treatment, to completely destroy all prospects of a crop of fruit, in many cases within a very few days. The trees are attacked at the period of bud swelhng and blossoming, when they are most susceptible to injury. These minute insects come literally in swarms, and may, if left alone, completely destroy all of the fruit buds of an orchard in four or five days. Many cases have been known where a delay of four or five days in spraying resulted in loss of the entire crop of fruit, and in some cases half of all the buds were killed in three days after the thrips appeared on the trees in great numbers. In view of this condition it is very evident that any means of control must be very thorough and done in the most exacting manner at the proper time. EXPERIMENTS IN THRIPS CONTROL. Many experiments with soil fmnigaiits, fertilizers, and irrigation were made with the hope of killing the thrips while in the ground, Fig. 5.— The pear thrips: Pupa, greatly enlarged. (Original.) HOW TO CONTROL THE PEAR THRIPS. 7 but all of them have proved to be absolutely of no avail, or at most impractical and expensive. In most cases the general vigor and health of the trees were improved by early fall irrigation and by the application of fertihzers. CULTIVATION. Thorough plowing in the fall in prune orchards planted on gravelly and sandy soils gave very helpful results. Success by deep plowing, cross plowing, and harrowing in October and November was fairly gen- eral in all experiments tried in Santa Clara County in the fall of 1908 and 1909. This manner of cultivation, when carried out to a depth of from 7 to 9 inches, resulted in killing from 60 to 80 per cent of the thrips present in the soil, but was not a sufficient control, as enough thrips escaped to cause great injury to the buds the following spring. SPRAYING. A long list of insecticides was tried out in spraying experiments, both in the laboratory and by spraying the trees in the spring. All poison sprays had to be al^andoned because of the inability to poison the thrips, as })oth adults and larvae do not feed in a way to be sub- ject to poisoning. Sticky sprays were difficult to apply and proved ineffective, as they do not retain this quality long and the thrips seem capable of moving around on almost any kind of surface. Dust sprays and preventive sprays had to be abandoned because the dust sprays failed to kill and the rapid swelling of buds and continued appearance of new surface area gave the thrips plenty of feeding ground and exposed phices of entrance into the buds. Success with contact sprays seemed more apparent; of these, various caustic sprays, such as caustic-soda and carbolic-acid solutions, gave excel- lent results in killing the thrips, but were, as a rule, unsafe because of injury to the trees. Solutions of tobacco extract were very promising, and when used at sufficieat strengths killed all the thrips actually reached, but they lacked sufficient penetrating quality to enter the swelling buds, a con- dition absolutely necessary, especially on pears, as most of the injury is done inside the cluster buds. Mechanical mixtures of various mineral oils and animal-oil soaps were tried and abandoned because of the difficulty of keeping them thoroughly mixed and the resulting injury to the trees caused by free oil separating out. Fish-oil soap emulsions with these various oils gave better results, the raw distil- lates running from 30° to 40° Baume being decidedly preferable over either the kerosenes or the heavy crude oils. A distillate-oil emulsion made according to directions (see pages 8-10) gave better penetration into the swelling pear buds than any other material which has been tried. There was one drawback, however; when this emulsion was used in sufficient strengths to kill all the 67859°— Cir. 131—11 2 8 HOW TO CO^^TROL THE PEAR THEIPS. thrips present or even a large percentage of them, there was consid- erable oil injur}^ to the buds. It was found that the weaker emulsions of from 3 to 6 per cent strengths had all the desired penetrating quali- ties and \nth Httle or no injurious effect upon the trees. As the nico- tine solutions killed all the thrips present and gave no spray injury tliis led to a combination of the two in Contra Costa County in the spring of 1909 Tsdth most satisfactory results. A tobacco extract containing 23 per cent nicotine, diluted at the rate of 1 to 60 in a 6 per cent distillate-oil emulsion, Idlled all the thrips touched and penetrated well into the pear cluster buds. The pubescent covering of the individual buds in the cluster, being resist- ant to water, seemed to act on the dilution in distillate-oil emul- sion in much the same manner as the wick upon oil in a lamp. Vari- ous other combinations of nicotine solutions \\ith 'Mime and sulphur solutions" and 'Mysol solutions" and ''soap solutions" were tried extensively, but none proved to be as effective and at the same time as practical as the combination of distillate-oil emulsion and the nico- tine solutions. DISTILLATE-OIL EMULSION. Homemade preparation. — Because of its cheapness and greater efficiency as a penetrating spray, and therefore a more satisfactory killing agent, growers are strongly advised to make their own emul- sions and, preferabl}', the soap, although the latter can usually be depended on if bought from reliable dealers. Directions for molcing. — To make soap use this formula or some multiple of same: Water G gallons. Lye (98 per cent) 2 j)<)un(ls. Pish oil \\ gallons. Put the water in a caldron or boiler and add the lye. When the lye is thoroughly dissolved and the water boiling, pour in the fish oil, stir- ring in the meantime, and boil slowly for two hours. When the soap has boiled sufficiently it should give a ropy effect when stirred and brought up upon the ladle. This formula gives about 40 ])()un(ls of moderately firm soap. Growers are cautioned to buy only genuine fish oil and not a fish- oil compound or a mixture of fish oils and vegetable oils. Herein lies part .of the secret of the penetrating efiiciency of the distillate emul- sions made by using animal-oil soap as the einulsifier. The cost of the soap is SO. 0105 per pound made from fisli oil at 35 cents a gallon. The (hstillate-oil stock emulsion should be made as follows: Formula:" Uot water \'l gallons. Kish-oil or whale-oil soap 30 j)oun(ls. Distillate oil (raw) 'M)° to :i4° r.aunie 20 gallons. a For a spray tank of 200 gallons capacity, live times lliis formula can be made at one time. HOW TO CONTROL THE PEAR THRIPS. 9 Have the water boiling hot when put into the spray tank and add the soap immediately while the agitator is running at a good speed. When the soap is all thoroughly dissolved, pour in the oil slowly, keeping the mixture well agitated while the oil is going into the tank. When all the oil is in and well mixed, pump out through the nozzles at good pressure (not less than 175 pounds) into storage tanks. No one should attempt to make this stock emulsion without a power spraying machine, as thorough agitation and high pressure are important requisites. Also, care should be used in having measure- ments reasonably exact, the water boiling hot, and soap thoroughly dissolved, before any oil is put in. This stock emulsion contains approximately 55 per cent oil, and to make a 3 per cent emulsion use 5h gallons of this stock in each 100-gallon tank. To dilute, first put the stock emulsion in spray tank (have the agitator going), and then add the water, keeping the agitator running all the time. Tliis is important with the commercial preparations as well as with the home- made emulsions. For the combination sprays of oil emulsions and nicotine solutions, the nicotine should be added last, that is, after the oil emulsion has been diluted to the desired strength. These solu- tions should not be mixed together without first diluting one of them. This concentrated emulsion will cost the grower about 5 cents per gallon, as most of the various distillates used for spraying cost from 5 to 10 cents a gallon in drum lots. In the spraying season of IDIO many growers of Contra Costa County experienced great difficulty in making emulsions that would remain emulsified when diluted. Part of this trouble was due to the varying degrees of hardness in the water, but more to the composition of the oil, especially where the treated oils and in some cases ordinary stove distillates were used. Even after these treated oils were emul- sified by changing the amount of soap used and treating the water to ''soften" it, the result was not satisfactory, as the diluted emulsion from this lacked the essential penetrating quality and had a tendency to collect in large drops rather than to spread out in a thin film. Experiments conducted thus far indicate that success is more uniformly obtained by using an untreated raw distillate 32° to 34° Baume with comparatively high flashing point. Some of the treated oils have given good results, but as a whole the untreated raw, straight distillates, comparatively free from naphtha and with a high flashing point, have given far better and more general satisfaction. Some of the oil companies, particularly in the Bakersfield and Coalinga districts, put out raw short-cut distillates — that is, the first distillate after the naphtha, gasolines, etc., have been removed. This kind of oil when running 32° to 34° Baume should under all cir- cumstances be given preference. The ordinary stove distillates have not, as a rule, given as good satisfaction, possibly because they 10 HOW TO COXTEOL THE PEAR THKIPS. contain too much of the light gaseous oils, which lower the flashing point. There are several commercial preparations of oil emulsions and miscible oils on the market, but these have not given as satisfactory results against the adult thrips as the homemade preparation, espe- cially on pears, on account of the noticeable lack of penetration into the cluster buds. Besides, all of these commercial preparations are far more expensive. Allowing 25 cents per hour for labor in making the soap and the concentrated homemade emulsion, the commercial preparations cost the grower from 2 to 5 times more than the more efficient homemade preparation. COMMERCIAL RESULTS. During the season of 1909-10 many large-scale experiments and demonstrations were carried out in pear, prune, and cherry orchards to determine more conclusively the efl'ectiveness of this combined spray and to put the treatment on a commercial basis; also, that growers might see for themselves the results of the work and know the monetary gain possible by such control measures as are recom- mended. The commercial results from some of these experiments are given below: PRUNES, SANTA CLARA COUNTY. The 16-acre prune orchard belonging to ^Ir. P. Landon, situated in the Willows district, near San Jose, CaL, consists of some of the largest and finest prune trees in the valley. The trees, which are about 25 years old, are planted 20 feet apart and the branches now overlap between the rows. The orchard has very heavy sandy loam and has been well cultivated and usually irrigated twice each year. Thrips became injurious in the year 1906, increasing greatl3Mn 1907, and causing much injury over the entire orchard, so that instead of a normal crop of a hundred or more tons of green (unchied) i)runes the entire 16 acres produced only IS tons of green fruit. Injury by the thrips was worse in 190.S, the yield that 3'ear being only 10 tons of green prunes. Demonstration fok 1909. Id the fall of 19()S, under direction of the Bureau of Entomology, Mr. I^andon plowed and cross plowed this orchard to a depth of 9 inches, with thorougli liarrowing after each plowing. Thri})s were very abundant in the soil, there being sometimes as many as 8,000 to the scpiare foot. The following table, giving the emergence of adults in s|)ring from samples of soil taken before and after plowing, shows that a])proxi- iiiately 70 percent of Ihe thrips were killed by cultivation: HOW TO CONTROL THE PEAR THRIPS. 11 Table VI. — Number of adult thrips emerging from cages containing samples of soil taken before and after plowing — Landon prune orchard, 1908-9. Plowed and cross plowed. Before plowing. Cage I. Cage II. Cage III. Cage IV. Cage V. Cage VI. 475 389 607 115 1,175 1,474 Average number of thrips per cage before plowing 1, 364 Average number of thrips per cage after plo\\'ing and cross plowing 396 Percentage li\'ing in treated areas as against the number of thrips living in un- treated ground per cent . . 30 Approximate percentage killed do 70 In the spring of 1909, 5^ acres of this 16-acre orchard were spraved three times; twice before blooming, for adults, the first application March 8 and 9, just as cluster buds were spreading, and the second Fig. 0.— Powlt sprayer at work in Landon prune orchard, 1909. (Original.) application March 16 and 17, just as the white tips of the petals were beginning to show. The third application or larval treatment was put on April 11 and 12, after most of the petals had fallen. For aU sprayings a gasoline-power outfit, with tower platform and three leads of hose, as sIiowtl in figure 6, was used, two men spraying from the ground and one from the tower to cover the tops of the trees. The material used was tlie recommended 3 per cent homemade distillate- 12 HOW TO COXTROL THE PEAR THRIPS. oil emulsion with commercial tobacco extract Xo. 1, added at the rate of 1-60, and the cost of the three applications was $157.38, the labor required in spraying being three men at $2 per day and one team at $2.50 per day, making a total of $8.50 per day, or a total of $51 for the six days; gasoline for the engine cost $2.40; plowing and cross plowing the previous fall, $26.65, making a total cost of $237.45 for the combmed treatment of plowing and spraying the 5J acres, or $44.54 per acre, an average of $0,449 per tree. The yield from tliis plat was 45 tons of green prunes, making an average yield of 8.44 tons per acre, or 155.17 pounds per tree. The prunes when dried averaged 54 to the pound, giving a commercial value for the plat of $1,710, or a value of $320.82 per acre, or an average of $2,948 per tree, as the prunes were sold on a 2J-cent basis for dried prunes averaging 80 to a pound. Plat II. — The rest of the orchard, comprising 10§ acres, and which only had the plowing and cross plowmg in the fall of 1908, at the cost 2_|^^^bk^ xS^ Fig. 7. — Diagram showing yield in green prunes i)er acre upon the sprayed, plowed, and check blocks, Landon prune orchard, 1909: o. Sprayed and plowed, 367.93 boxes, value $320.82 per acre; b, plowed block, 8.5.G5 boxes, value S74.85 per acre; c, check block, 7 boxes, value $6.65 per acre. (Original.) of $5 per acre, or $0,046 per tree, yielded 21 tons of green prunes, or an average of 1.97 tons per acre, or 36.45 pounds per tree, giving a commercial value of the plat as $798, or a value of $74.85 ])er acre, averaging $0,692 per tree. J*l(it III, check. — This plat, em])racing 5 acres of the ])nme orchard beloiigmg to Mr. F. Cottle, and immediately adjoining the Landon orchard and of the same kind of soil and with similar trees in re^rard to size and ])re^d()us care, received no treatment for thri})s. The total yield was 1,750 ])ounds of green ])runes, or an average yield of 350 pounds per acre, or 3.24 poimds ])er tree, representing a commercial value of $33.25 for the plat, or an average of $6.65 ])er acre or $0.06 ])er tree. Tlie yield and value per acre upon the three ])lats is shown diagrammatically in figure 7. Tlie average gain j)er acre U})()ii Plat I was obtained after adding tlie total cost of treatment per acre to the value of the crop ])cr acre IVoiii the check ])lat, and subtracting tliat amount from the value of HOW TO CONTROL THE PEAR THRIPS. 13 the yield per acre upon Plat I. This gave a net gain of $269.53 per acre as returns upon an investment of $44.54, or a gam of about 600 per cent. The gain upon this plat due to the spraying alone was $199.88 per acre, or $1.85 per tree. Plat II, which received only the plowing and cross plowing, gave, after adding the cost of the treatment to the yield per acre upon the check plat and subtracting the total from the yield per acre upon Plat II, a gain of $63.20 per acre for an investment of $5, or about 1,200 per cent on the investment. Owing to the lateness of the third application on Plat I, the larvae caused considerable scabbing on the fruit, and the difference in quality of the fruit from Plat I and Plat II was not as great as would have been the case had the larval application been applied a few days earher. Results, 1910. During the faU of 1909 part of the orchard was irrigated and the entire 16 acres were plowed to a depth of 8 inches in November. One small block was cross plowed. The entire orchard was harrowed several times after the plowing. Plowing Results. Soil samples were taken in similar cages as in the previous year and yielded the following results: Cage No. Treatment. II I Before plowing Il-a I Plowed once IV Before plowing I V-a Plowecl once I Before plowing I-a Plowing and cross-plowing. Total number thrins. 2,813 3.53 3.379 1..306 2,731 27 Per cent killed. The average percentage of thrips killed by one plowing was 71 per cent and the average number killed by plowing and cross plowing 98 per cent. No spraying was done in 1910, except a few trees for other experi- ments. Results. — All of the trees on the 16 acres came into heavy bloom, but only the 580 trees of Plat I and one block of about 80 trees which was sprayed for larvae in 1909 set a heayy^ crop, as man}^ thrips were present in the rest of the orchard. The trees sprayed in 1909 were stronger, and so many of the thrips had been killed by the treatment that the accumulative results showed almost as great a difference in the crop yield for 1910 as was the case in 1909, when the spraying was actually done. LIBRARY 14 HOW TO CONTROL THE PEAR THRIPS. The primes averaged 57 to the pound, and computations made on the basis of 5 cents for prunes running 80 to the pound. The different yields and values were as follows: Plat I — Demonstration Uoclc of 1909, consisting of 580 trees. — This block pelded 35 tons 212 pounds of green prunes, worth $2,109.87 for 580 trees, or $3.63 per tree or $392.04 an acre. Plat II — Sprayed for larvx in 1909, 80 trees. — This block yielded 2 tons 676 pounds of green prunes, worth $140.51 for 80 trees, or $1.99 per tree or $214.92 per acre. (This was part of Plat II in 1909.) Plat III — Remainder of orchard, consisting of 10 acres, not sprayed in 1909. — This block pelded 1\ tons of green prunes worth $450.75 for 1,080 trees or 10 acres, making $0,417 a tree or $45,075 an acre. An examination of the above statement of yields and values shows that great headway can be made the first year in eliminating the thrips injury from an orchard by thorough spraying and that a con- siderable benefit extends into the second year. Demonstrations for 1910. The 6J-acre prune orchard belonging to Mr. H. Curry was plowed and cross-plowed in November, 1909, to a depth of 11 inches and har- rowed after each plowing. The block was then sown to barley for a cover crop wliich made a good growth and was at spraying time nearly 3 feet high. Examination of two samples of soil 17 by 17 inches square, taken before plowing, and two of the same size taken after plowing, showed tliat approximately 61 per cent of the thrips were killed. Plat A. — In adcHtion to the fall plowing, this block of 300 trees received three applications of commercial tobacco extract No. 1 com- bined at the rate of 1 to 66 with 3 per cent homemade distillate-oil emulsion. The first spraying was applied March 7, just as the cluster buds were spreading. The second for adidt thrips was made March 1 7, as the tii)s of the ])etals were showing. The third application, wliich was for the larvie, was made April 6, after most of the ])ctals had fallen. In all of the spraying an effort was made to direct the spray into the end of each bud and to drench the trees thoroughly. Plat B. — This plat, consisting of 98 trees, received the cultivation, but no spraying. Results. — The first application was made too late to obtain best results, and a large number of buds w^as so far advanced that it was diflicult to reach all of the thrips. A series of counts showed that all of the exposed thrips were killed and about 30 per cent of those within the buds. The second application killed practically all the thrips left on the trees (over 90 per cent), as the bud clusters were spreading at this time. A fair port ion of the blossoms set fruit on the HOW TO CONTROL THE PEAR THRIPS. 15 sprayed block and some on the plowed block, but the fruit on the latter continued to drop until picking time. The yield upon the various plats is shown diagrammatically in figure 8, and was as follows: Plat A yielded 16,254 pounds of green prunes, or 8,127 pounds of dried prunes, from the 300 trees. This made an average yield of 5,849.92 pounds of green prunes per acre, or 54.166 pounds per tree. Plat B yielded 1,032 pounds of green prunes or 516 pounds of dried prunes from the 98 trees, or an average of 1,138.32 pounds per acre, or 10.54 pounds of green prunes per tree. Plat C, consisting of 10 acres, was left untreated to serve as a check for comparison, and yielded 860 pounds of green prunes, or 430 pounds of dried prunes, for the 1,080 trees. This gives an average yield of 86.4 pounds per acre, or 0.8 pound of green prunes per tree. ^riinenls in pear orilmrds, Contra Costa County, Cal., I'.iU). (Original.) TIMING THE APPLK ATIOXS. The spraying must ])c done on time, and for best resuUs all the trees should be treated within a few days. During the season of 1910 more of the failure to get satisfactory results was due to lateness of ni)i)lica- tion than to any other one cause. Thrips were in the trees and in great numbers before many of {\w growers ])m-chase(l tlu^ir s))raying supplies, and in many cases half the buds weic entii(dy desti'oycd and the others badly injured before th(» trees had Ixmmi giv(Mi even the lirst application. The growei' should have (everything in I'cadiiuv^s, all materials on hand, concentrated emulsion mach' u|), and spray machin- ery in j)erfect working or(h'r by the lirst of March and have all other orchard woik in such sha|)e that when the thiips appear in numl)ers HOW TO CONTROL THE PEAR THRIPS. ^1 the spraying may be done at once and before the buds have been seriously injured by the feeding of the adults. The grower should have enough spray machines to cover the orchard quickly. At least one good power outfit is necessary for every 30 acres of orchard. SCHEDULE OF APPLICATIONS. In badly infested orchards three applications are necessary the first year for controlling the pear thrips. Two of these sprayings should be directed against the adults and one against the larvse, and to obtain satisfactory results must be timed properly. First application. — The first spraying should come as soon as the thrips can be found on the trees in numbers. This will usually be the first two or three days of March, just as the earliest buds are separating slightly at the tips. In figures 12, 13, and 14 are shown photographs of the more advanced buds of Bartlett pear, Imperial and French prunes, and Black Tartarian cherry, which were taken at time of first application. Second applica- tion. — The second spraying, whichis also for adults, should come from four to ten days after the first, depending some- what on VarietV of ^'"- 12.— Bartlctt pear cluster buds showing stage of earliest buds at p ., , „ " , , lime of first spraying against thrips. (Original.) rruit, stage or bud development, and rapidity of emergence of thrips from the ground. On pears this will usually be just as the earliest cluster buds are spreading, and on prunes and cherries when the tips of the petals first begin to show. Both of these applications are important and necessary to insure the pnxkiction of a good croj) of uninjured blossoms. The nozzles should be held close to the bud clusters and the spray directed into the ends of tlie buds. This makes it necessary that the spraying be done mostly from above. Third application. — The third s})raying is for larvae and properly comes just as most of the petals are falhng from the trees, depending somewhat upon the variety of fruit. In any case the small, w^hite, active larvae can be easily seen, and when they first become abun- dant spraying should be done. In this larval spraying on cherries and ])runes where tlu^re is a large amount of leaf surface exposed, the 22 HOW TO CONTROL THE PEAR THRIPS. spray should be directed first against the underside of the leaves, beginning with the lowest branches and spraying upward. Most of the larvae are feeding on the under surface of the leaves, and spraying the upper surface first would serve to knock the larvae from the trees without their coming into contact with the spray. Angle nozzles of the iyY*e shown in figure 15, giving coarse, penetrating spray, should be used for all applications. MATERIALS TO USE. The combination of 3 per cent homemade distillate-oil emulsion, made from raw distillate, 32° to 34° Baume, and the nicotine solutions. a h Fig. n.—a, French prune buds; b, Inipt^rial prune buds; stiowinR stago of earliest buds at time of first application against thrips. (Original.) is given ])referenco over all other s])rays used so far. To dilute, measure out 5 J gallons of the stock emulsion for each 100-gallon spray tank, or 1 1 gallons for a 2()()-gall()n tank; start the engine; ])our the stock cinulsiou into the s])ray' tank, and while the agitator is nmning, add the \vat(M- to fill u]) the tank, ])iitting in the strong nicotine solution last and after the stock emulsion has been diluted. Foi- spraying in the inlciior counties add to this dilute oil-emulsion HOW TO CONTROL THE PEAR THRIPS. 23 commercial tobacco extract No. 1, which is a dark, ahiiost viscous Hquid containing 2.75 per cent nicotine, at the rate of 1 to 75; or tobacco extract No. 2, which is a H^rht-colored hquid containing 40 per cent of almost nonvolatile nicotine at the rate of 1 to 1,500, or a fraction more than a pint to a 200- gallon t ank. This form of the nicotine has been higldy efficient and will in all probability be more satisfactory than the former. By reason of its greater concentration the handling and transportation charges will ])e much less ; also, the nicotine contained in this preparation is much less vola- tile, thus allowing the use of a smaller amount of actual nicotine in the dilu- tion, as it remains an active killing agent for a longer time on the trees. In Santa Clara County greater dilutions than these have been found to be satisfactory, due most likely to different climatic conditions, evapo- ration there being much less at this time than in the interior counties where the atmosphere is drier. Grow- ers in the Santa Clara Valley are advised to use the 3 ])er cent distillate-oil emulsion, with tobacco extract No. 1 added at the rate of 1 to 100 or tobacco extract No. 2 at the rat(» of 1 to 2.000. These recommendations hold for all thri])s sprayings, for both adults and larva^ and on all varieties of deciduous fniits attacked by the ])earthrips. No or- chards should be sprayed, however, when the trees are in full bloom. All spraying for adults should be done before the blos- soms appear and spraying for larvae after a large proportion of the petals have fallen. In the prune orchards of Santa Clara Valley deep fall plowing and cross-plow- ing has proved a valuable and profita- ble aid in controlling th{^ tlirips. Those who can do so are strongly advised to irrigate their orchards in September or October, and when the soil is in ])roper condition ])low with disk plows to a depth of 7 or Fig. 14. — Buds of Black Tartarian cherry at time of first application against thrips. About one-half natural size. (Original.) Fig. 15.— An^le nozzle of the large cham- ber type used in spra>ing experiments. (Original.) 24 HOW TO CONTROL THE PEAR THRIPS.