Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. VIRGIN ISLANDS AGRICULTURAL EXPERIMENT STATION, LONGFIELD SMITH, Agronomist in Charge, St. Croix, Virgin Islands, U. S. A. BULLETIN No. 1. Under the supervision of tlie STATES RELATIONS SERVICE, OflSce of Experiment Stations, U. S. Department of Agriculture. SEA ISLAND COTTON IN ST. CROIX. BY LONGFIELD SMITH, Agronomist in Charge. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1921. VIRGIN ISLANDS AGRICULTURAL EXPERIMENT STATION, LONGFIELD SMITH, Agronomist in Charge, St. Croix, Virgin Islands, U. S. A. BULLETIN No. 1. Under the supervision of the STATES RELATIONS SERVICE, OflBce of Experiment Stations, U. S. Department of Agriculture. SEA ISLAND COTTON IN ST. CROIX. BY LONGFIELD SMITH, Agronomist in Charge. Issued May 23, 1921. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1021. VIRGIN ISLANDS AGRICULTURAL EXPERIMENT STATION, ST. CROIX. [Under the supervision of A. C. True^ Director, States Relations Service, United States Department of Agriculture.] E. W. Allen, Chief, Office of Experiment Stations. Walter H. Evans, Chief, Division of Insular Stations, Office of Experiment Stations. STATION STAFF. LoNGFiELD Smith, Agronomist in Charge. Charles E. Wilson, Entomologist. LETTER OF TRANSMITTAL. Agricultural Experiment Station, St. Croix, Virgin Islands, October 4, 1920. Sir: I have the honor to transmit herewith a manuscript on the growing of Sea Island cotton in St. Croix, and. to recommend that it be published as Bulletin No. 1 of the Virgin Islands Station. Respectfully, LoNGFiELD Smith, Agronomist in Charge. Dr. A. C. True, Director States Relations Service, U. S. Department of Agriculture, Washington, D. C. Publication recommended. A. C. True, Director. Publication authorized. E. T. MiaiEDiTH, Secretary of Agriculture. 2 SEA ISLAND COTTON IN ST. CROIX. CONTENTS. Introduction Improvement by s«^ed selectiou. Hybrid cottons Selection experiments Method of planting Time of planting Fertilizing Care after planting Page. 3 4 Page. Cotton picking 0 Sunning, whipping, and cleaning 10 Ginning and marketing 10 Yield 10 Some diseases and pests of cotton 10 Fungus and bacterial diseases 10 Insect pests 11 Plat experiments, 1010-20 14 INTRODUCTION. Sea Island cotton seed was imported into the Virgin Islands from Barbados about 1908, and cotton raising has become one of the prin- cipal industries of the islands Trhere the soil and climate are well suited to its cultivation. The area devoted to it, though at present small, is jDroducing very well, the average yield of seed cotton in 1919-20 being around 1,000 pounds per acre. One of the plats at the experiment station produced at the rate of 4,-150 pounds of seed cotton per acre. Since the establishment in 1911 of the agricultural experiment sta- tion, the aim has been to secure varieties of cotton which are resistant or immune to the blister mite {Eriophyes gossyini) and which also possess a heav^^ bearing character with extra long, fine lint. Work in cotton breeding during the past year produced Hnt of excellent quality, the fiber being fine, strong, and silk}^ ; and one variety of cot- ton showed practically complete immunity to the blister mite. Greater production per acre is needed, more especially now that the whole world is demanding more cotton for clothing, textiles, fabrics, and the like, and the station will continue its experiments to obtain a higher yield per acre of first-class cotton. The following table gives the yearly export of lint and cotton seed from the Virgin Islands since 1909 Amount of lint nn'l cotton seed r.rported from the Tirgin Islands, 1900-191.'). Year. Lint. Cotton seed. Year. Lint. Cotton seed. 1909 Pounds. 219,040 243, 323 2.50, 02.5 2t]3. 794 Poundx. 569,414 467, 288 582,-504 545, 603 Pounds. 132,909 3.56,205 m, 463 Pounds. 376,776 1910 1914 1911 1915 1912 30716=—21 3 4 BULLETIN 1, VIRGIN ISLANDS EXPERIMENT STATION. All of the cotton produced was exported to Liverpool. On account of the European war which started in 1914, the exportation of cotton lint became almost impossible and the cultivation was practically abandoned. The experiment station at St. Croix, however, kept up its cotton-breeding work, so that when exportation again became pos- sible, seed of improved cotton would be available for the planters who desired to produce this staple. Cotton planting has not been resumed to the same extent as formerly, owing to the increasing interest in sugar which has brought very high prices. In 1919' about 200 acres only were planted to cotton, and it is unlikely that a much larger acreage will be planted on the island if sugar continues to bring high prices. EXPERIMENTS IN IMPROVEMENT BY SEED SELECTION. When the experiment station was established in 1911 the Sea Island cotton fields showed considerable mixture of wild cotton and cot- tons having an undesirable habit of growth and abnormal boll drop- ping. Work was at once begun to improve these conditions. Two varieties of purebred Sea Island cotton. Sterling and Cameron 106, were imported from Barbados and planted at the experiment station in plats ranging in size from three-fourths to 1 acre each. From these, individual plants were selected for further improvement. A careful record was kept of the weight and quality of the lint of all selected plants, and the following year the best specimens were placed in plats of about one-fifth acre each. In 1913 the seed from the best plants was planted in plats of 4 to 5 acres each, and in 1914 seed from these was distributed to the various estates in St. Croix. Thus, within three years after starting the cotton experiments, the station was distributing seed of pedigree cotton to planters. In the mean- time new selections were being made each year to keep up the improve- ment and purity of type. In 1913 and 1914 the cotton-breeding plats occupied approximately 40 acres of experiment station ground. The work has been kept up continuously, though on a much smaller scale in later years, and the cotton now grown in the island is practically all produced from pedigree seed raised by this station. In addition to improving and purifying the Sea Island cotton seed of the island, experiments were undertaken to find some new varieties which might possibly be more remunerative than the ordinary Sea Island type. To this end the varieties Sakellaxidis, Caravonica, Southern Cross Upland, and Virgin Gorda Native were imported and crossed with Sea Island varieties. During two seasons Sakellaridis, an Egyptian variety of cotton, was found to give yields no higher than Sea Island cotton, and se- lected plants did no better. This cotton can not be recommended, SEA ISLAXD COTTOX IX ST. CROIX. 5 since its lint, being shorter and less silk}', is considerably less valuable than that of the Sea Island cotton. Southern Cross long-staple upland cotton gave yields of lint in- ferior to Sea Island cotton, and the quality of the lint being also infe- rior, this cotton can not be recommended. Caravonica cotton gave poor results, and individual selections showed little improvement. After trying it out for three seasons it was eliminated from the experiments. Virgin Gorda Xative cotton possessed very good lint, and the plants were considerabh^ improved by selection. The variety, how- ever, proved very susceptible to flower-bud maggot, and for that reason it was eliminated from the tests. Other crosses were made between Sea Island and a wild variety of cotton common in St. Croix. The local wild variety, though having very poor lint, shows complete immunity to the blister mite, which is a serious pest of cotton in the island. Considerable impor- tance is attached to the outcome of these crosses. HYBRID COTTONS. The first generation of hybrids, the result of a cross between Sea Island cotton and Sakellaridis, was found to be excellent, the plants yielding a wonderful amount of lint of a quality fully equal to that of the Sea Island parent. It was found practical to raise large quan- tities of first-generation hybrid seed by hand pollinating a Sea Island plat early every morning with pollen of Sakellaridis. This work was done early in the morning before the pollen from the newly opened Sea Island flowers had much chance of being spread on the stigmas by any agency. The flowers treated were not emasculated or bagged, but the pollen of Sakellaridis was simply dusted on the stigma of the Sea Island variety and the flower marked with a tape. About TO per cent of the resulting seed will be crossed. Inas- much as the lint is very similar to that of the Sea Island cotton, it will hardly be affected by admixture, and the yield may be almost doubled by the process. In 191-i three acres were planted with seed obtained in this way, and the yield obtained was 1,046 pounds of seed cotton per acre. During 1914, which was a poor year for cotton, the best pure Sea Island plat yielded only GOO pounds of seed cotton. In 1913 a small plat of first-generation Sea Island crossed with Sakellaridis yielded at the rate of over 3,000 pounds of seed cotton per acre. Owing to lack of funds and time to devote to following up this work, the station lost the pure seed of Sakellaridis cotton. The second-generation plants of Sea Island cotton crossed with Sakellaridis show consideral)le variation, but when selections are made fix)m these the third generation comes fairly true to seed, and 6 BULLETIN 1, VIRGIN ISLANDS EXPERIMENT STATION. further selections continue to come almost true. Some of these are still being grown at th6 experiment station. Crosses were made between Sea Island and Southern Cross Upland cotton with favorable results in the first generation. The lint of this generation equals that of the Sea Island parent, and the yield is good. The plants, furthermore, show a special resistance to the leaf-cut disease, which in wet seasons does considerable damage to cotton in the Virgin Islands. Subsequent generations of this hybrid show a multiplicity of types, few of which are any good and none of which comes true to seed. Some selections of the best have been under experiment for several generations and are still being grown with a view to finding eventually a good one which will come true to seed. Sea Island crossed with St. Croix Native gave good results the first year they were tried in the first generation, as the plants were almost completely immune to blister mite. Furthermore, it was found that the plants could be ratooned and thus made to give large yields the second year. (Eatooning of ordinary Sea Island cotton is impossible because the ratoons come up infested with blister mite.) The lint of the hybrid is not as good as that of the pure Sea Island. However, the results of this crossing were so successful that the sta- tion planted a 10-acre plat early in May, 1914, to hybridized seed. The results were disappointing. The plants suffered severely from boll dropping and were so severely attacked by cotton stainers that the yield of lint was rendered very low. The experiment has not been repeated, though it is thought that it might be worth while to try it again, planting the next time in July or August. The first-genera- tion hybrid seed can be readily made in any quantity by the method suggested above for producing Sea Island crossed with Sakellaridis. When this seed is planted it is easy to pick out and pull up the un- crossed Sea Island plants which differ markedly from the crossed plants. A stand consisting entirely of first-generation crosses can be obtained by planting five or six seeds in each hill, and by removing those plants which are not crosses. During the first year the yield of lint from the crossed plants is much the same as that of pure Sea Island. The advantage of raising this type lies in the possibility of ratooning it, since it is immune to blister mite, and ordinar}^ Sea Island cotton can not be ratooned because at the end of its season's growth it is always killed by this pest. In ratooning, plants should be cut down to within 1 foot of the ground, and all branches burned to destroy stainers, scales, and other pests. The station hopes to re- peat this experiment in the near future to determine definitely whether it will pay to raise this hybrid. Though immune to blister- mite attacks, the first generation resulting from Sea Island crossed with Native is susceptible to attack by cotton stainers. This diflS.- culty may preclude the possibility of ratooning. SEA ISLAXD COTTOX IX ST. CKOIX. 7 When the seed of the first-generation hybrid is sown the plants split into a great variety of types. Some plants are completely stferile, producing no flowers ; other plants produce flowers yet ripen no fruit; others again entirely lose an erect habit and trail on the ground; and the lint characters are highly variable in each plant, the majority being of little value. Selected plants of the second generation present the same bewildering number of tj'pes when their seed is sown. The station is finding it extremeh' difficult to extract a pure type by repeated selection; nevertheless, it will continue its experiments for this purpose. Experimental work with cotton has had to be much curtailed owing to lack of funds to carry it on. Since the receipts for sales of products do not accrue to the station, but are deposited in the United States Treasury, the area formerly cultivated has been much re- stricted. Were the station to keep the money received for cotton sold, the experiments could be made to pay for themselves and the station continue to provide the island with pure seed. SELECTION EXPERIMENTS. Much work has been done in selecting plants from all the planta- tions of the island. When the experiment station was inaugurated the fields of cotton contained a considerable mixture of types. From these the best types were selected, and the selections repeated from year to year. As a result, the station now has a large variety of types of long-linted cottons. Some of these are very promising. In fact, they may in the future displace the pure Sea Island cotton now grown in the island, all of which has been obtained by repeated selections from Cameron 106. METHOD OF PLANTING. In St. Croix it was customary to prepare ground for cotton plant- ing by plowing it to the same depth as for cane planting—that is, 8 or -9 inches. After plowing, the land was harrowed and scored into shallow furrows 44 feet apart with two cuts of a small vinej^ard plow drawn by mules. The seed was planted in the furrows in hills 3 feet apart, some fi^'e or six seeds being placed in each hill. When the plants reached a height of probably 6 inches they were thinned out to one plant per hill. When the writer came to St. Croix in 1911 he was confronted with the problem of boll dropping and leaf-cut, or tomosis. In fields where the cotton was growing luxuriantly the young leaves would acquire a curling and crimpling habit, while the flower buds would abort, turning black and dropping off when only the size of a pin's head. Xo organism or fungus could be found associated with this condition, and it was observed that the more luxuriant the vegetative 8 BULLETIlsr 1, VIRGIN ISLANDS EXPERIMENT STATION. growth the worse was the leaf curl. It was further noted that one or two rows around the edges of nearly all the fields would almost invariably be superior to the cotton plants inside the field. The plants on the outside grew less luxuriantly, but were of better shape and full of bolls. In some cases this difference in condition was very marked, a fact which was attributed to the compact nature of the land around the edges of the fields where the plow had not been able to do thorough plowing. This deduction was later confirmed by an examination of a field at Mount Pleasant plantation, where a heavy rainfall occurred, causing the young cotton in one part of the field to be almost submerged for a number of days. The cotton in this part of the field was much stunted in growth ; but later, on account of its freedom from leaf curling, it bore a much superior crop to the rest of the field. The water, being on the soil for some days, had compacted the land. The experiment station has recommended that plowing for cotton be shallow, not exceeding 4 or 5 inches, and this recommendation has been followed with success by many planters. Eolling the land before planting is also recommended, as this reduces the leaf curl and enables the plants to acquire a better habit of growth and to give larger yields. In other respects the method of planting remains the same, except that the rows are now usually made 4 feet apart. TIME OF PLANTING. Just before the experiment station was started a law was passed by the Colonial Council calling for a closed season for cotton for one month in each year. All cotton plants in the island had to be uprooted and burned by a certain date named each year by the regu- larly appointed commission, and no sowing of cotton could take place prior to the lapse of four weeks from that date. The period for clearing was one and the same for all growers. This law gave rise to much dispute and bitterness, some growers having planted earlier in the year than others. The greater part of the cotton was planted by one large plantation company whose director believed in early planting because cotton was planted early in neighboring Eng- lish islands. To fall in with his ideas, everybody had to pull out his cotton early, and it often happened that the fields of late planters were laden with bolls at the very time fixed by the commission for uprooting and burning. The writer was finally instrumental in getting the governor and members of the Colonial Council to change this law so that different closed-season periods would be allowed in the several parts of the island. This change was much appreciated by the smaller growers and has worked very satisfactorily. The writer has come to the conclusion, SEA ISLA2sD COTTOX IX ST. CROIX. 9 after many years of experience with and obseryation of cotton grown at different periods, both at the experiment station and elsewhere, that July to September, inclusiye, is the best time to plant cotton in St. Croix. Very early planting—in May, for instance—causes the first bolls to ripen in September, when usualty the rains are heayy. When cotton plants that are laden with bolls are subjected to heayy rains a large amount of boll dropping usuall}^ occurs, and the cotton that opens is spoiled. Probably August and September are the best months to plant cotton here. Very good returns can be obtained, howeyer, by planting as late as October. During the past two years unusually large yields were had by the majority of growers who planted in September and October. FERTILIZING. In these islands it is not customary to manure land that is to be planted to cotton. An area that has been grown to cotton for some years would doubtless benefit by the application of manure to the soil. The appearance of most of the cotton fields here seems to indicate, howeyer, that the soil does not need fertilization. In fact, the fields are often evidently too fertile for the cotton, producing a rank growth resulting in coarse and unproductive plants. Soils at the east end of the island are deficient in lime and it is probable that lime appli- cations would result in increased yields in this area. The East End has always suffered most severely from boll dropping and leaf curl. East End growers, though repeatedly urged to experiment with lime applications, have so far not done so. Cotton grown in other sections of the island is usually planted in rotation with sugar cane on soils containing plenty of lime. Fertilizing is unnecessary on soils where such rotation is practiced as the sugar-cane land is generally well fertilized with farmyard manure before planting. It is thought that experiments with artificial fertilizers on land to be planted to cotton would be of interest and value, but up to the present these have not been undertaken. CARE AFTER PLANTING. In this island the custom is to keep the soil between the rows of cot- ton well stirred by means of a 2-shovel cultivator drawn by mules. This is an excellent practice, but should not be continued too late in the season for fear of root pruning and consequent dropping of bolls. COTTON PICKING. Cotton picking is usually done by women and children, who are paid about 2 cents for each pound. Formerly the price was 1 cent a pound. A woman can pick 40 to 60 pounds of seed cotton daily. The 10 BULLETIN 1, VIRGIN ISLANDS EXPEEIMENT STATION. cotton is not picked as clean as it should be. Too much trash and dirt are picked along with the cotton ; and it is almost impossible to make the laborers understand that they must put the stained cotton in a bag- separate from that for white cotton. The picking of clean cotton, however, should be insisted upon, as the whipping process designed to remove trash and dirt can be made cheaper and perhaps dispensed with altogether when diligent care is exercised in the picking process* SUNNING, WHIPPING, AND CLEANING. Seed cotton is usually spread out in long trays to be sunned for a day before whipping. This operation consists in striking the seed cotton on a piece of stout mesh wire forming the bottom of the tray. "When the dirt has passed through the tray, the stained and weak cotton, all leaves, and hardened bolls are picked out. GINNING AND MARKETING. After being cleaned the cotton is sent to be ginned and baled. At present there is only one gin in operation here. Formerly there were three. About 26 or 27 per cent of lint is obtained from the seed cotton. St. Croix cotton hitherto has been sold in England, where it brings a high price. This year (1920) it sold for $1.80 to $2 a pound. YIELD. Accurate figures on yields of cotton in St. Croix are not available, but it is thought that during the years 1911 to 1915, inclusive, 500 pounds of seed cotton per acre was about the average. Some fields have jdelded 1,000 and 1,100 pounds to the acre. Others have not yielded more than 100 or 150 pounds to the acre. The low yields in East End were no doubt due to a combination of causes, principally adverse rainfall conditions, the showers in that section being very heavy and usually followed by severe droughts ; the leaf-cut disease, or tomosis, which was probably greatly helped by the unfavorable climatic and soil conditions; and the presence in great numbers of the stinkbug {Nezara viridula)^ which owes its existence to the numerous wild massambee {Cleome viscosa) and fireweed {Datura metel)^ on which it lays its eggs. SOME DISEASES AND PESTS OF COTTON. FUNGUS AND BACTERIAL DISEASES. Bacterial disease of cotton [Bacterium raalvaccarum) ^ known un- der the various names of angular leaf-spot, black-arm, boll-spot, round-spot, mildew, and internal boll-rot, all make their appearance in the fields, together with anthracnose {Colletotrichum gosspyii)y SEA ISL:iXD COTTOX IX ST. CROIX. 11 due to a parasitic fungus. A rust, probably due to unfavorable soil conditions, is not infrequently found, and a ^vilt, due to a fungus {Fusarluin va-sinfectum)^ is noticeable after heavy winds. ^Mil- dew and rust are not very serious, as they do not appear until toward the close of the plant's life. Angular leaf-spot seems to do consider- able damage, especially when the bacterium attacks the stems and causes black-arm. Under good cultural conditions, however, this disease is not troublesome. The most serious of the diseases is in- ternal boll-rot, which is spread by punctures of cotton stainers and green stinkbugs. The boll-rot could be controlled were measures adopted to exterminate these pests. In order to check fungus diseases, all cotton seed should be soaked in corrosive sublimate solution. 1 part to 1,000 parts of water, for 10 minutes before planting. INSECT PESTS. The Cottox Staixeb (Di/sdcrcus andrece) And the Green Stinkbug {yezara viridula). Only one variety of cotton stainer {Dysdercus andrece) occurs in St. Croix. Since the greatest damage wrought by this insect is the spreading of internal boll-rot, efforts should be made to eliminate the pest as soon as it appears. This can best be done by ha^-ing the stainers knocked from the bolls into pans containing a little water and kerosene. The gi'een stinkbug {Xezara viridul4- 00 cc -1 < Bui. 1, Virgin Islands Agr. Expt. Station Plate II. SEA ISLAND COTTON IN ST. CEOIX. 13 Cotton Bollworm s.^ These worms frequently cause much damage to cotton in St. Croix, and they are especiall}' severe on cotton grown at the east end of the island where they occur in numbers. Among the species attacking bolls and flower buds the following have been found : Heliothis ohso- leta^ Prodenia oimithogaJl'i^ P. Jatifascia^ Laphygma frugiferda^ and Xylomyges s~imia. The amount of damage which Heliothis obsoleta is capable of doing can somewhat be realized when it is stated that young cater- pillars before pupating, when kept in captivity, devoured between 30 and 36 young buds and bolls apiece. The pest is most numerous during September and October. Cotton planted in May and June, consequently, alwa^'s receives the worst attacks. There is little or no danger of infestation in late-planted cotton, that is, cotton planted in September and October. Spraying plants with lead arsenate would probably be a fairly effective means of dealing with these pests. In passing from one boll to the next they have to eat through the bracts and the rind of the boll and in so doing get enough poison after a time to kill them. Paris green impregnated with lime is not likely to be so useful for this purpose as lead arsenate, since it does not stick to the leaves but is readily washed off the plants by a light shower. The poison to be effective should be firmly glued to the plants. At the experiment sta- tion traj^s containing molasses were laid among the plants for the purpose of collecting the moths, from 8 to 10 trays being placed on every acre of land. Very excellent results were obtained by the use of the molasses, and some of the East End planters who used this method of control also reported good results. Kerosene tins cut in half lengthwise make splendid trays and are about the cheapest to use. Black molasses can be obtained at small cost from the sugar factories. Bollworm-attack first causes a flaring of the bracts. Later the young buds and bolls drop off. Older bolls may remain firmly at- tached to the plants. It is suggested that all fallen buds and bolls be collected and burned daih^ FLOWER BUD MAGGOT. In certain years flower bud maggot does considerable damage, and it is generally worst when the cotton is planted early. During the j^ast two years, when nearly all cotton was planted in September and October, no flower bud maggots were observed. The presence of the maggot is made known by the the flaring of the bracts of the flower buds. xVn examination of the flower buds will show whether ''While this publication was going through the press the pink bollworm ( PcctinopJiora gossijpieUo) was reported on St. Croix. 14 BULLETIN 1, VIRGIN ISLANDS EXPERIMENT STATION. this condition is due to flower bud maggot or to bollworm. The maggots are very minute, about the size of a small pinhead, and pink- ish in color. Several are found in one flower bud, and they spring out when the buds are opened. CUTWORMS. Sometimes cutworms are very troublesome among the newly- planted fields, cutting down the young seedlings as they appear above ground. If they are very troublesome they can be destroyed by means of a poisoned bait composed of 50 pounds of bran and 1 pound of Paris green mixed into a paste with molasses and water. A bit of this mixture can be dropped at each hill. COTTON APHIS. This insect occurs abundantly on young cotton in this island, espe- cially when the weather is dry. It causes the leaves to assume a curled and blistered appearance and seriously checks the growth of the young plants. However, no permanent injury to the crop has yet been observed, probably because as the insects become abundant their natural enemies (ladybird larvseand syrphus-fly larvae) increase in numbers sufficient to destroy them. PLAT EXPERIMENTS, 1919-20. During the season of 1919-20, 127 plats of individual cotton-plant selections were grown at the experiment station (Pis. I and II). The plats were planted in September, 1919, and harv^ested at the end of April, 1920. Owing to lack of funds to carry on the work the plats had to be very small, consisting for the most part of 25 to 50 hills each. The largest yield obtained was at the rate of 4,450 pounds of seed cotton per acre. Two plants of this plat produced 2 pounds of seed cotton each. The lint of this variety was 1.75 inches in length, and was comparatively free from blister mite. The next largest yield was at the rate of 2,862 pounds seed cotton per acre. The lint of this cotton was 1.8 inches long, and the plants were only little attacked by blister mite. The third largest yield was at the rate of 2,724 pounds of seed cotton per acre. The lint was 2 inches in length, strong, and of fine quality, but the plants suffered severely from blister mite. The average yield of 16 of the plats was over 2,000 pounds of seed cotton per acre, and only 15 plats fell below 1,000 pounds per acre in yield. The lengths of the lint ranged from 1.5 to 2.2 inches; the lint lengths, like blister-mite resistance, were variable. One plat only showed complete immunity to this pest. O