oy : ; eves SB 818 cai 8 ENT Issued January 9, 1911. eS VEPAKT MENT OP VAGRICU L tiie. BUREAU OF ENTOMOLOGY—CIRCULAR No. 181. HOW TO CONTROL THE PEAR THRIPS. BY S. W. FOSTER anp P. R. JONES, Agents and Experts. WASHINGTON : GOVERNMENT PRINTING OFFICE : 1911 67859°—Cir. 131—11——1 d, BANEAS A BUREAU OF ENTOMOLOGY. L. O. Howarp, Entomologist and Chief of Bureau. C. L. Maruart, Assistant Entomologist and Acting Chief in Absence of Chief. R.S. Currron, Executive Assistant. W. FP. Taster, Chief Clerk. F. H. CuitrENpDEN, in charge of truck crop and stored product insect investigations. A. D. Hopxins, in charge of forest insect investigations. W. D. Hunter, in charge of southern field 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. Puixurrs, in charge of bee culture. D. M. RoGers, in charge of preventing spread of moths, field work. Routia P. Currie, in charge of editorial work. Mase. Cotcorp, librarian. Decipuowus Fruit Insect INVESTIGATIONS. A. L. QUAINTANCE, in charge. Frep. Jonnson, S. W. Foster, E. L. JENNE, P. R. Jones, A. G. Hammar, C. W. Hooxer, J. R. Horton, W. Postirr, J. B. GiLL, agents and experts. E. W. Scort, J. F. Zimmer, entomological assistants. (Cir. 131] (11) CIRCULAR No. 131. 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 pyri Daniel.) By 8. W. Foster and P. R. Jonzs, Agents and Experts. DISTRIBUTION. The pear thrips (Luthrips 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. 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 \ \ prow jmee b insect, the rapidity Fic. 1.—Map showing area infested by pear thrips in California. of its spread over (Original. ) large areas, and the suddenness of attack in great numbers—completely blasting in a few SAN BERNARDINO a 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. b Journal of Economic Biology, vol. 4, No. 2, 1909. 2 HOW TO CONTROL THE PEAR THRIPS. 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 year 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 years 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 by this species is caused by 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 larvz 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 larve 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 prunes 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 which is often followed by more or less fermentation, especially before blooming. The feeding by larve on prunes after blooming causes the well-known thrips ‘‘scab,” while most of the scarred and misshapen pears are caused by the work of the adults. LIFE HISTORY. Adulis—The adults (fig. 2) or winged form of the thrips first appear on the trees about the middle 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- aie Le ge ZB eee SS : a. SAAN ANNININ Hf i ee MMMM AK Fig. 2.—The pear thrips (E£uthrips pyri): Adult, greatly enlarged. (Original.) tion of the tables of emergence records (Tables I to V) will show the dates of emergence for 1909-10: TaBLeE I.—Total daily emergence of thrips from all cages at laboratory, San Jose, Cal., 1909 and 1910. Number | Number | Number | Number : thrips thrips thrips thrips Date. emerging | emerging | Date. emerging | emerging in 1909. in 1910. in 1909. in 1910. Feb. 9 0 25 Mar. 8 219 275 10 0 18 9 776 144 11 0 16 10 497 100 12 0 16 11 498 73 13 0 4 12 338 179 14 0 88 15 313 45 15 18 22 14 248 20 16 0 27 15 279 Ui 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 22 119 129 21 2s | |Szaneneone. 23 135 375 22 at ee See ee 24 552 272 23 115 Fi Wee Sah 25 459 297 24 Sees Meee 26 444 455 25 2) t\ (eee ce eee 27 414 574 26 Bb lease cee | 28 781 657 27 ha Eh Sea Se | Mar. 1 781 1,975 28 eh | eee cek eee od 2 535 3, 592 29 UN eae ao ee 3 1, 299 3,011 30 Be) | rare caeve pee 4 714 4,217 31 Oils eee | 5 508 1, 402 Apr. 1 BS |e ae ae 6 362 1, 595 2 OM eee =, 7 438 539 3 Ll eee. eres 2 | HOW TO CONTROL THE PEAR THRIPS. EMERGENCE RECORD FOR CoNTRA Costa COUNTY. TasLe I1.—Emergence of thrips from cages placed in ground under trees in pear and prune orchards, Walnut Creek, Cal. 1909. Number | Date. of thrips emerging. Feb. 13 0 16 20 19 37 | 22 30 26 110 Mar. 2 615 5 679 10 752 12 273 16 65 20 33 | 22 4 27 11 | | 1910. Number Date. of thrips emerging. Feb. 21 1 23 4 25 23 27 36 Mar. 1 56 3 237 5 1,170 i 2,110 9 892 11 1,778 13 557 15 198 17 71 19 3 21 6 27 5 TaBLE III.—Emergence of thrips from soil samples taken from December and kept in cages at laboratory, Walnut | 1909. 1910. Number |, Number Date. of thrips Date. of thrips out. out. | Feb. 12 3 Feb. 18 11 15 42 20 16 16 56 22 0 17 38 24 12 18 56 |) 26 30 20 89 28 75 23 125 | Mar. 2 377 25 185 || 4 918 27 246 |) 6 937 Mar. 1 196 8 165 4 237 || 10 114 7 51 || 12 47 10 D2] 14 0 14 13 16 4 19 0 22 0 orchard in November and Creek, Cal. EMERGENCE REcoRD FOR SOLANO County, 1910. TABLE IV.—Emergence of thrips from cages placed in ground under trees in orchards, Suisun, Cal. Date. Number of thrips emerging. rOoOCOow Number Date. of thrips emerging. Feb. 27 20 Mar. 1 47 3 121 10 484 16 1 TaBLE V.—Emerge HOW TO CONTROL THE PEAR THRIPS. 5 nce 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. emerging. 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 ‘ 612 23 2 12 357 24 5 16 82 25 11 19 8 | 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. Eqgs.—As soon as the first leaf surfaces or fruit stems are exposed egg laying usually begins, depending somewhat on the variety Fig. 4.—The pear thrips: Larva, greatly enlarged. (Original.) 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 10th 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. Larve.—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 larve (fig. 4) are beginning to appear in numbers. The very first larve can usually be found about March 20, and are in maxi- Fia. 3.—The pear thrips: Eggs, high- ly magnified. (Original.) 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 larvee drop from the trees, of their accord or with falling calyces, or are blown by wind or knocked off by rain. After the 6 HOW TO CONTROL THE PEAR THRIPS. middle of April the number on the trees diminishes rapidly, and by the last of April all the larve 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 tiny cell, where they remain until the following spring. Pupz.—The larve mostly remain as such in these cells till Sep- tember, when pupation begins, pupe (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 larve, pupe, 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, im many cases within a very few days. The trees are attacked at the period of bud swelling and blossoming, when they are most susceptible to injury. These minute insects come literally Fic. 5.—The pear thrips: Pupa, greatly in swarms, and may, if left alone, ee ae 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 fumigants, fertilizers, and irrigation were made with the hope of killing the thrips while in the ground, HOW TO CONTROL THE PEAR THRIPS. 4 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 fertilizers. 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 abandoned because of the inability to poison the thrips, as both adults and larve 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 places 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 sufficient 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° Baumé 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 CONTROL THE PEAR THRIPS. thrips present or even a large percentage of them, there was consid- erable oil injury 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 with little or no injurious effect upon the trees. As the nico- tine solutions killed all the thrips present and gave no spray injury this led to a combination of the two in Contra Costa County in the spring of 1909 with most satisfactory results. A tobacco extract containing 2? per cent nicotine, diluted at the rate of 1 to 60 in a 6 per cent distillate-oil emulsion, killed 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 ina lamp. Vari- ous other combinations of nicotine solutions with ‘lime and sulphur solutions”? and ‘‘lysol 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, preferably, the soap, although the latter can usually be depended on if bought from reliable dealers. Directions for making.—To make soap use this formula or some multiple of same: WiatliehetecSen seh soe hges to Se Se eee Bee ee 6 gallons. Lave (OS. per Cent) 2. sen sten stem eee ee emia 2 aes oe 2 pounds. LFTs so | SR git ARS ce OS in eee ou oe an co a 1} 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 pounds 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 efficiency of the distillate emul- sions made by using animal-oil soap as the emulsifier. The cost of the soap is $0.0165 per pound made from fish oil at 35 cents a gallon. The distillate-oil stock emulsion should be made as follows: Formula:@ EHot water. <5 2: sch: eee eee aoe eee 12 gallons. Fish-oil orwhale-oil suap: sscase eee ets. ee ee 30 pounds. Distillate’ oil. (raw) 30° to 34°. Banmeé 22272 ss 20 gallons. @ For a spray tank of 200 gallons capacity, five times this formula can be made at one time. HOW TO CONTROL THE PEAR THRIPS. 9 Have the water boiling hot whem 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 54 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. This 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 1910 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° Baumé 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° Baumé 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 CONTROL THE PEAR THRIPS. 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 effectiveness 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 Mr. 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 greatly in 1907, and causing much injury over the entire orchard, so that instead of a normal crop of a hundred or more tons of green (undried) prunes the entire 16 acres produced only 18 tons of green fruit. Injury by the thrips was worse in 1908, the yield that year being only 10 tons of green prunes. DEMONSTRATION FOR 1909. In the fall of 1908, under direction of the Bureau of Entomology, Mr. Landon plowed and cross plowed this orchard to a depth of 9 inches, with thorough harrowing after each plowing. Thrips were very abundant in the soil, there og sometimes as many as 3,000 to the square foot. The following table, giving the emergence of adults in spring from samples of soil fen before and after plowing, shows that approxi- mately 70 per cent of the thrips were killed by cultivation: HOW TO CONTROL THE PEAR THRIPS. Ab | 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. ba £4 ——_____ Cage I. Cage IT. 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 plowing and cross plowing. ..---.-.--- 396 Percentage living in treated areas as against the number of thrips living in un- LRGAe Me omO Ut Cue eet = hed Were Up ee Rt cern te rena, eee rere See per cent... 30 AMMroOMmnaALespereentage deed: 2). cia. 28 O00) ASS oe ot Sete doze 70 In the spring of 1909, 54 acres of this 16-acre orchard were sprayed three times; twice before blooming, for adults, the first application March 8 and 9, just as cluster buds were spreading, and the second Fic. 6.—Power 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 all sprayings a gasoline-power outfit, with tower platform and three leads of hose, as shown 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 the recommended 3 per cent homemade distillate- 1 HOW TO CONTROL THE PEAR THRIPS. oil emulsion with commercial tobacco extract No. 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 combined treatment of plowing and spraying the 5} acres, or $44.54 per acre, an average of $0.449 per tree. The yield from this 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 2}-cent basis for dried prunes averaging 80 to a pound. Plat IJ.—The rest of the orchard, comprising 103 acres, and which only had the plowing and cross plowing in the fall of 1908, at the cost BRE TAN names a b c Fic. 7.—Diagram showing yield in green prunes per acre upon the sprayed, plowed, and check blocks, Landon prune orchard, 1909: a, Sprayed and plowed, 367.93 boxes, value $320.82 per acre; b, plowed block, 85.65 boxes, value $74.85 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 per acre, averaging $0.692 per tree. Plat III, check.—This plat, embracing 5 acres of the prune orchard belonging to Mr. F. Cottle, and immediately adjoming the Landon orchard and of the same kind of soil and with similar trees in regard to size and previous care, received no treatment for thrips. The total yield was 1,750 pounds of green prunes, or an average yield of 350 pounds per acre, or 3.24 pounds per tree, representing a commercial value of $33.25 for the plat, or an average of $6.65 per acre or $0.06 per tree. The yield and value per acre upon the three plats is shown diagrammatically in figure 7. The average gain per acre upon Plat I was obtained after adding the total cost of treatment per acre to the value of the crop per acre from the check plat, and subtracting that 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 gain 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 larve 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 earlier. Resutts, 1910. During the fall 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. Prowina RESULTS. Soil samples were taken in similar cages as in the previous year and yielded the following results: Total Cage No. | Treatment. number Fe ecie | thrips. ee LU sce Si PS Ss a eee Before: plowilP