Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices Peers Me A a ae Ws aaa f\ CIRCULAR No. 295 “DECEMBER 1933), UNITED STATES DEPARTMENT, OF nenicott ny’ i WASHINGTON, Dc. Da eos = _U, S, DERN THE OBSCURE SCALE ON THE PECAN AND ITS CONTROL » By Howarp Baker,! assistant entomologist, Division of Fruit and Shade Tree Insects, Bureau of Entomology CONTENTS Page Page ANT ETO GUM CEO Ms see ee ee ae RE Ip Nabil Gomis seo ek ee 10 INaarelo fein ute eee oe eee ea eee 2 Dormant spray applications_____-_-___-- 10 General description of the stages__----------- 3 Summer spray applications___________--- 15 Mifesnistorywandehabitses 22 eee ieee eee 5 Recommendations for control____-_-_.--- 16 INH AOA CovAR) Sane a a re a ee el 8 Formulas used in preparing lubricating- IPATASILCSe ere estan ne Ue ee Lee 8 OUSTAVUTL ST OTA Ses eee ge Predators © saree tes ted he a Se 9 Specifications of oils used________-______- 17 HD) ISCASES see een EEO Se ese De 4S LATTA ATS Veen es aC Io OI ae ete a 18 Literaturencitedice ses see See wee ee ln nen wee 19 INTRODUCTION Because of the prevalence of the obscure scale in Louisiana pecan orchards, the increasing demands for recommendations for its control, and the wide variation in the control measures that have been recom- mended, a study of its biology and control was made from 1929 to 1932, inclusive, at the pecan insect laboratory of the United States Bureau of Entomology at Shreveport, La. The results of these investigations are reported briefly in this circular. The obscure scale (Chrysomphalus obscurus Comst. )* was first described in 1880 by Comstock (2, p. 303),° when he found it attacking the willow oak (Quercus phellos) in the District of Columbia, and was first reported as a pest of the pecan by Herrick and Harned in 1909 (6), when they found it attacking the pecan in Mississippi. This scale is probably a native pest, as it has not been reported from an foreign country. It has now been reported from nearly all of the ter- ritory from Massachusetts south to and including Florida and west to include Illinois, Kansas, Oklahoma, and Texas (fig. 1). It is usually found on oaks and hickories but is occasionally found on other plants. The pecan is a favorite host plant, and this scale insect is a serious pest on both seedling and improved varieties in Texas, Louisi- ana, Arkansas, Mississippi, and Alabama. It formerly attracted only occasional notice, but, with the increasing importance of the pecan industry, it has lately come into more prominence. In general, the measures recommended for its control have been those which have proved satisfactory for related scale insects, but in many instances they have been inadequate. Most writers (, 7, 9) have quite generally agreed that lime-sulphur, at whatever 1 The author expresses his appreciation of helpful suggestions received from G. F. Moznette of the pecan insect laboratory of the U.S. Bureau of Entomology at Albany, Ga. 2 Order Homoptera, family Coccidae, subfamily Diaspinae. 3 Italic numbers in parentheses refer to Literature Cited, p. 19. 4485°—33——1 2 CIRCULAR 295, U.S. DEPARTMENT OF ‘AGRICULTURE strength, will fail to give control. Recommendations for the use of oil sprays have varied widely, miscible oil sprays being generally recommended for use at a dilution of 1 part stock solution to 15 parts water (7), whereas oil emulsions have been recommended for use at strengths ranging from 2 to approximately 11 percent oil in the diluted emulsion (3, 4, 5, 9). NATURE OF INJURY The obscure scale attacks all parts of the tree proper and in cases of severe infestation has been found on leaf and leaflet stems, but never on the leaves themselves or on the nuts. As there is but one generation a year this scale must, for self-preservation, develop on those parts of the tree which remain alive the entire year, for it can not live on dead plant tissue. FIGURE 1—Map of the United States showing the distribution of the obscure scale (Chrysomphalus obscu- rus). The black area indicates those States in which it is an important pecan pest and the cross-lined area indicates additional States in which it has been found. The initial infestation commonly starts in slight depressions in the bark surface or about the buds. The scale tends strongly to develop at first on the lower, inner portions of the tree, the infestation building up gradually until the parts first attacked are completely encrusted, while it spreads slowly and gradually toward the terminal portion of infested branches. A badly infested branch will usually be killed before much of an infestation has been built up on its terminal portion. Very few trees have been noted on which all parts have been attacked alike. More often the incrustation is heavy on one or more of the main leaders and their branches, or one side of the tree, whereas the remainder of the tree shows only a slight infestation. The examination of a number of moderately infested felled trees has shown that little or no scale develops in the upper third of them. On small to moderate-sized heavily infested trees the scale infesta- tion reaches more nearly to the top. The general appearance of the scale mass on an infested tree or branch is that of a roughened deposit on the surface of the bark (fig. 2). e OBSCURE SCALE ON THE PECAN AND ITS CONTROL 3 Attack-by this insect results in the gradual killing of brancnes. Those most commonly killed range in size fronr the smallest up to those approximately 3 inches in diameter. Branches thicker than 3 inches are seldom killed, though they may be weakened to such an extent that they will not produce normally if at all. The slow progressive killing of infested branches gradually reduces the number of fruiting limbs, besides weakening the whole tree and rendering it more subject to attack by borers or other insects, and diseases. Trees lacking proper fertilization, cultivation, and care are the most often seriously infested, but many trees in well-cared-for orchards have also been found seriously infested. GENERAL DESCRIPTION OF THE STAGES The entire life of this scale insect, except the brief presettling, or crawler, stage and the short active life of the adult male, is spent FIGURE 2.—A ppearance of an infestation of the obscure scale on pecan: A, A partly encrusted infestation; B, a completely encrusted infestation. X 8. beneath the protection of a waxy scale covering. At all other times the insect is concealed and cannot be seen without first removing the scale covering. The eggs are ellipsoidal, about 0.25 mm long, light purple to laven- der, and frequently have a whitish bloom. The young, or crawlers, appear as tiny indistinct specks moving over the surface of the bark. They are oval and pale salmon-pink, save for the tiny orange-colored rear end, or pygidium. The pygidium retains its orange color through all of the stages in which it is present. After finding a place to settle, the young insects begin to secrete scales which are at first white and circular, but soon become slightly longer than broad, and gradually take on the coloration of the surface on which they rest (fig. 3). The first-stage larvae beneath the covers soon become silvery with a pink tinge, but are otherwise like the crawlers save for their gradually increasing size. 4 CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE The second-stage larvae have no appendages except their mouth parts; and their bodies, which are but slightly longer than broad, narrow somewhat posteriorly, and are pale yellow. The males can first be distinguished from the females about the middle of the second stage, when they become more elongate and pink, and develop two pairs ‘of rudimentary eyes. The adult females are slightly wrinkled and still pale yellow until the developing egg mass within the body gives them a purple appear- ance. When full grown they are but slightly longer than broad, being about 1.25 mm long by 1.20 mm wide. As the time for egg extrusion nears, the last body segment is drawn up so that the body is about four fifths as long as broad (fig. 4, A, c). The male propupae have no mouth parts or pygidia but retain their coal-black rudimentary eyes, regain the rudimentary antennae and FIGURE 3.—The obscure scale on pecan bark: A, A single male scale specimen; B, two female scales. X 8. lees, and develop wing pads. They are salmon-pink, oval, and slightly less than 1 mm long. The pupae are like the propupae in size and shape, their antennae, wing pads, and legs are further developed, and a prominent pro- tuberance, or anal style, is present at the rear end for the first time. The adult males are tiny, frail, salmon-pink to brick-red, flylike insects with a mahogany-colored band across the thorax and a long anal style. The covers of adult females are slightly convex, somewhat irregular in outline, slightly longer than broad, and about 3 mm (about one eighth inch) in length. They blend in color with that of the bark surface on which they rest, being of varying shades of gray to black, ae have a prominent lip at the rear end when full grown (figs. 3, B, and 4, A). OBSCURE SCALE ON THE PECAN AND ITS CONTROL 5 The covers of the males are nearly oval and slightly over half as large as those of the females. They blend in color with that of the surface on which they rest, and if viewed ventrally, show two white longitudinal ridges, one along each side of the body of the developing male (fig. 4, 6). LIFE HISTORY AND HABITS The eges are formed within the body of the female and can first be seen about the first of April. As they become fully developed, they are pushed out by the female a few at a time and partly fill the cavity left beneath the scale cover by the retraction of the last body seg- ment of the female. The first eggs are usually found extruded between the middle of May and early June, and the first young, or crawlers, can be found a few days later. Both eges and crawlers are present in large numbers throughout June and until the middle of FIGURE 4.—Ventral views of the obscure scale: A, Female scale covers showing the lip at the posterior end, the molted skins in a and c, and the retracted shrunken body of an adult female in b, X 6; B, male covers showing the white longitudinal ridges, X 6. July, after which they gradually decrease in numbers until by the first of August but few remain. Scattered specimens may be found until late in September or early in October. Data indicate that each female may produce about 150 eggs and that, under favorable eaten, slightly over 100 of these will develop into crawlers that settle The crawlers may settle beneath the cover of the parent or other old scale, or in the open on some other portion of the host. The first newly settled young are always found beneath old scale covers. ‘Those that go outside settle within a few hours and usually not far from the parent scale. Data obtained in January and early February 1931, representing nearly 30,000 specimens from three Shreveport orchards, showed that 84.44 percent of the live specimens were females and 15.56 percent were males. Of the live females 62.63 percent were set- tled under old scale covers and 37.37 percent were outside, while only 5.72 percent of the males were settled under old scale covers. These 6 CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE data are valuable from the standpoint of control and may explain, in’ part at least, the wide variation in the recommendations which have been made for the use of oil emulsions in controlling this insect; for experiments have shown that it is difficult to obtain a complete con- trol of that portion settled under old scale covers, especially in en- crusted infestations. Consequently, the higher the percentage of specimens developing under old scale covers, or the older and heavier the infestation, the heavier the concentration of oil likely to be needed in the spray solution to effect a satisfactory control. — The newly settled young begin almost im- mediately to form their covers, and by the end of 6 to 8 hours these are usually sufficiently developed to conceal them. The covers are at first pure white, but by the end of the second day after theirformation they becomelight brown; by the end oi the first week, dark brown; and by the end of the second week they begin to take on the color of the sur- face on which they rest, so that by the time the scales are ready for the first molt the coloring of the covers blends closely with that of the sur- roundings. It is evident that this insect is able to incorpo- rate into its cover some portion of the surface on which it develops, ——— - — 7 for the color of its cover FIGURE 5.—Two immature individuals of the obscurescalewhich glwavs blends with it. settled on or near a line made with black india ink: a, Specimen = left in place showing a portion of it in contact with the black Figure 5 shows where line; b, specimen removed showing the portion of the line gone two specimens settled on where it was formerly covered by the scale cover. 20. here it was formerly covered by the scale cover. X See ‘PRS “Adie line, one of which, at a, has not been touched, while the other, at 6, has been removed. It is to be noted that that portion of the cover of the specimen at a which is in contact with the black line 1s black while the remainder of the cover blends with the bark on which it rests. That the line was actually incorporated into the cover 1s evident from an examination of the place from which the specimen at 6 has been removed, which shows the line to be missing where 1t was crossed by the removed cover and to be intact beyond what was the outer margin of the cover. This would seem to indicate quite clearly that the insect is able to utilize the surface of the bark on OBSCURE SCALE ON THE PECAN AND ITS CONTROL i which it settles in the formation of its cover and by this use biend itself into the coloration of the surrounding bark surface. In figure 6 is shown the light appearance of the scale covers on a light-colored bark. The first molt begins about 5 to 6 weeks after settlement, and sec- ond-stage larvae appear about 1 week later. By the middle of Sep- tember practically all normally developing specimens (about 50 to 60 percent of all that settle) have reached this stage. No other change in development is to be noted save for a gradual increase in size until : e@ FIGURE 6.—A group of individuals of the obscure scale on a very light-colored bark. Compare these with the scales shown in figure 2. X 12. about the middle of October, when some of the males can be distin- oeuished from the females for the first time. From this point devel- opment of the two sexes proceeds along different lines. The females continue to increase in size until about the first of December, when the older ones begin to enter the stage preparatory to the second molt, followed shortly by the remainder, with practi- cally all specimens completing the change by the last of January. The females remain in this stage until development into the adult stage 8 CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE is started—usually some time between the middle and last of Febru- ary. The second molt is usually completed and the first adult females noted about 2 weeks after development is resumed, or between the first and middle of March, and by the middle of April practically all normally developing females have reached the adult stage. The males, which can first be distinguished from the females about the middle of October, continue differentiation from then until, by the middle of November, practically all of them can be distinguished. Fhe males begin transformation to the propupal stage the last of January and to the pupal stage in late February or early March, reaching the adult stage at about the same time that the females are undergoing the final change to adult, or some time in late March or early April. The height of the male emergence period has ranged from the middle of March to the middle of April. Although provided with wings, the males are not strong fliers, and their active life is short—only a day or two at the most. They have been observed fertilizing females shortly after their emergence, frequently visiting one after another in rapid succession. - Eggs may be observed forming within the bodies of the females shortly after fertilization, or, usually, some time during the first half of April. Thus the life history from egg to egg shows this insect to develop only one generation each year. Limbs infested with the obscure scale have been collected from time to time in orchards both north and south of Shreveport. These samples have been examined so that the stage of development of the scale specimens on them might be compared with that of specimens collected in Shreveport orchards at the same time. The variations found have not been great—2 weeks’ difference in development being about the greatest that bas been found. These data indicate clearly that this insect has only a single generation each year throughout its present known range. NATURAL CONTROL Parasites, predators, and diseases, the common natural-control agencies, exert an important influence upon the number of specimens of the obscure scale which are able to develop from crawler to adult. It is difficult to arrive at an accurate estimate of the benefit derived from these agencies, because of the long period through the year in which they work, and because by the end of the year many of the earlier-attacked specimens are destroyed by scavengers, drop off, or are so frayed that they cannot be distinguished from material similarly affected in previous years. PARASITES Four minute, wasplike parasites have been reared in numbers sufh- cient to indicate their importance in the natural control of the obscure scale. These species, in the order of their importance, are Prospaltella fuscipennis Gir., P. berlesii How., Physcus varicornis How., and Ablerus clisiocampae Ashm.* In addition to the species listed, one or a few specimens of additional probable parasites have been reared but not in sufficient numbers to indicate that they are of importance. Data show that parasites destroyed about 14 percent of the obscure scale during the 1931 season and about 21 percent during the 1932 season 4 Determined by A. B. Gahan of the Bureau cf Entomology. OBSCURE SCALE ON THE PECAN AND ITS CONTROL 9 in two Shreveport orchards. Less complete data from other orchards indicate that the above percentages give a fair idea of the numbers of parasites usually present. Naturally, these numbers vary some- what from orchard to orchard and from year to year. PREDATORS Predators exert their greatest influence during the period of egg and crawler development. The coccinellids, or lady beetles, which are important predators of other scale insects, are unimportant in con- nection with the obscure scale so far as has been observed. Mites, several species of which are present in considerable numbers at most seasons of the year, are largely scavengers, destroying old dead scales, but four species of mites have been observed to attack live individuals of the obscure scale. Specimens of Cheletia sp., Atomus sp., and Allothrombium sp.’ have been observed in a few rare instances to attack crawlers after they have emerged from beneath the parent scale cover but before they have settled. They are relatively unim- portant predators. A fourth mite, Hemisarcoptes sp.*, is an important predator as well as a scavenger. Examinations over a 3-year period of 600 females of the obscure scale shortly after they completed repro- duction showed them to contain an average of 15.93 unextruded eggs and to have an average of 20.03 unhatched extruded eggs plus dead unsettled crawlers remaining beneath their scale covers. The last- mentioned mite is responsible for a portion of these remaining eges and dead crawlers, as it attacks reproducing females, causing their premature death and consequent failure to finish the extrusion of their egos. It also attacks the extruded unhatched eggs and newly hatched crawlers before they emerge from beneath the parent scale’s cover. This mite has not been found in any numbers until after the egg- _ extrusion, crawler-emergence period is well advanced. Examinations of scale-infested material late in the season have shown nearly 100 percent of the producing females on some samples to be attacked by this species. Although this mite arrives too late to prevent a large portion of the crawlers from settling, it does arrive in time to destroy a portion of them and to cut short the reproduction. DISEASES Diseases, like parasites, are an important natural means of control of this scale insect. Two diseases have been found attacking the obscure scale, namely, Myriangium duriaet Mont. and Berk. and Sphaerostilbe aurantu-cola (B. and Br.) Petch.® Because these dis- eases occur over such a long portion of the year, it is not possible to make an accurate estimate of their work, but some idea of their value may be ascertained when it is considered that, with the help of para- sites, they are apparently holding this scale in check in some southern Louisiana pecan orchards in which artificial control measures are not being practiced. Although diseases may attack newly settled speci- mens as early as August and older specimens as late as June of the following year, their greatest development takes place during the winter and early spring. The examination of 29,714 specimens from three Shreveport orchards in January and early February 1931 5 Determined by H. E. Ewing of the Bureau of Entomology. 6 Determined by Vera K. Charles, of the Bureau of Plant Industry. 4485°—33——2 10 CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE showed 3,946, or 13.28 percent of them, to be affected by disease. An examination of scale-infested material from almost any southern Louisiana pecan orchard at this same period of the year would show a much greater percentage diseased. ARTIFICIAL CONTROL While parasites, predators, and diseases do their share in holding this scale insect in check, they cannot be depended upon to do so always or as effectively as is necessary. Consequently, it is necessary to develop some method of artificial control which can be depended on in _ time of need. DORMANT SPRAY APPLICATIONS During the last 3 years lubricating-oil emulsions, miscible oils, and liquid lime-sulphur have been tested at a number of strengths and applied at different times during the dormant period and at the de- layed-dormant period. ‘Preliminary experiments were carried out in two orchards early i in 1930, the results of which indicated that (1) the obscure scale is difficult to control effectively, (2) liquid lime-sulphur, even at a dilu- tion of 1 part of stock solution to 5 parts of water, and lubricating-oil emulsions containing 2 percent of oil in the diluted spray are ineffec- tive, giving practically no control, and (3) miscible oils, 1 part stock solution to 15 parts water, and lubricating-oil emulsions containing 4 and 6 percent of oil in the diluted spray can be depended upon to give a fair to moderate degree of, but not perfect, control. During the dormant season of 1930-31, lubricating-oil emulsions, miscible oils, and liquid lime-sulphur were tested again. Three oils of widely different characteristics were emulsified by two formulas and applied at concentrations of 2, 4, and 6 percent of oil in the diluted emulsion at three widely separated times during the dormant period in two different orchards. Two miscible oils were tested at a dilution of 1 part stock solution to 15 parts water, and liquid lime- sulphur testing 34° Baume was used at a dilution of 1 part stock solution to 7 “parts water. The results of these experiments are given in table 1. The results shown in table 1 indicate that (1) iubricating oils at equivalent dilutions are about equally effective whether emulsified according to formula 1 or formula 3, (p. 17); (2) about the same degree of control may be expected from spraying at anytime during the dormant season; (3) the characteristics of the oils used did not appear to influence the degree of control, indicating that any of the oils fall- ing within the range of those ordinarily recommended for use in dor- mant spray work (8) 7 should be about equaily effective; (4) 2-percent lubricating-oil emulsions are ineffective, not even civing a good con- trol of the exposed scales; (5) 4- -percent lubricating-oil emulsions are fairly effective, giving a ood control of the exposed scales and a fair control of those developing under old scale covers; (6) 6-percent lubricating-oil emulsions are reasonably effective, giving a good degree of control of the scales developing under old scale covers as well as of the exposed scales. The control effected by this dilution can be considered commercially satisfactory, since this scale has only one 7 Range of specifications ordinarily recommended for oils for use in dormant sprays: V a (Saybolt 100° F.), 90 to about 200 seconds; volatility, low; unsulphonated residue, not less than 50 percent. OBSCURE SCALE ON THE PECAN AND ITS CONTROL 11 generation each year, and the numbers are further considerably reduced by natural agencies; (7) miscible oils varied widely in effec- tiveness, giving generally poorer results than the 4-percent lubri- cating-oil emulsions but considerably better results than those given by the 2-percent emulsions. While far from satisfactory, they will, with the assistance of natural agencies of control, hold a scale infesta- tion in check; (8) liquid lime-sulphur was not effective. TABLE 1.—Results of spray experiments on the obscure scale on pecan trees, Shreve- port, La., 1930-31 [Approximately 1,000 scales were examined in each test except no. 22, in which approximately 3,000 scales were examined] Spray applied Spray applied Spray applied = : December 1930 February 1931 Sec ae Oil per- centage Seales dead Seales dead Scales dead or parts Test ‘ of = MH Fis no. Material used ! stock g & S solu- q S q tion to} 2 1p n a a a partsof| 3 | ye SC ee {\ys water a2 |eg 9 cS 8 9 S 3 ue} ad ~ uo} io) ms a |2ny tbe PO ASe tk” | Sp eM Slee ie |iger rent rnres enemas ee fo} o oC » fo) oO o .=) (o} oO a eae) yl a 5 q Salar $ q Ors 8 q = ry jo) iS) mo S) i) oS ial oO o ie) ie) (oD) cal Oo HY |n cal 12) BY |n HH Oo Per- | Per- | Per- | Per- | Per- | Per-| Per-| Per-; Per-| Per-| Per-| Per- cent | cent | cent | cent | cent | cent | cent | cent | cent | cent | cent | cent Heese Op alkse ve ses ee 2} 40.5} 10.1) 16.3) 8.6} 59.0) 24.8) 30.3) 21.2) 52. 5) 36. 5) 38.0) 24.6 pS Bases all ines doses ae: 4| 93.9] 68.1} 73.9} 71.5} 75.2) 48.1) 51.6} 45. 2) 60. 5} 66. 1} 67. 2} 60. 1 So erek ESS ors GO is Ee 6], 98.4] 84.5) 87.0) 85.8] 90.4} 72.8) 75.9} 72. 7| 87. 5) 88.9] 88.8] 86.4 7. eas OURO} eee 2) 63.5) 17.2) 26.0) 19.2} 72.6) 26.6) 34.7) 26.1} 60.4] 45.1) 45.9) 34.2 fleas eee |S Sta it Come io te 4| 91.1) 67.5] 72.2) 69.6] 95.6] 72.9) 76.5} 73.4] 73.0} 58.6) 59.5) 50. 7 Gaeea | es GObReiiibe Daye 6| 100.0} 87.1) 89.3) 88.3! 98.5] 74.8] 80.7] 78. 2) 95. 3) 89.7! 90.1! 88.0 Ev phvaka OG eet = 2| 68.2} 9.0) 21.8 14.6) 68.2} 21.1) 29.3] 20. 0} 54.4) 27.7) 29.5) 14.2 Sie ay | cae Oa: 4) 88.32} 33.0) 45.6; 40.6] 90. 2) 63.8] 60. 6) 55. 4] 87.1) 72.3] 73.2) 67. 4 Ohta gare gel as Gomi eres as) 6| 96.3] 77.6} 81.7} 80.0) 97.7] 77. 6] 83.6] 81.4) 92.3) 86.2) 86.5) 83.6 ATi] BOTA ee eS 2} 46.3) 10.8) 18.8) 11.4] 58.5) 26.1) 29.9} 20.7} 50. 0) 33. 8} 35. 2) 21.2 I ales a Oe ees: 4| 96.6) 78.5) 83.4) 81.9] 97.1! 78.0) 81.9] 79. 5} 67. 4) 50.3) 51.1) 40.5 MNO ers | ree Cl iene etn ens 6| 96.9} 92.4) 93.0) 92.4) 99.1] 97.7! 98.0) 97: 7| 88.8) 87.3) 87.4] 84.7 Te ae COU NA Ds aah se eS 2) 45.0) 10.7) 17.9} 10.4] 68.0} 26.9] 35. 4} 26.9; 53. 2) 28. 6) 30. 5) 15. 4 1 RE ee ae Goes aire eer 4; 95.8] 75.6} 78.5} 76.5) 95.3} 79.1] 81.8] 79. 4| 90. 6} 79.4) 80.1) 75.8 JESSE en eee COO) E A se a ORS 6} 100.0) 94.3) 94.9) 94.4) 90.4] 86. 5) 87.4) 85. 7| 94.4) 87.3] 87. 8} 85. 2 1G eee (Oss ae Tiere Ss 2} 46.6) 9.6) 18.3) 10.8) 47.8] 14. 5] 20.7) 10.3) 52.6) 32.9] 34. 8) 20.7 17 ERO Petes C6 Kays are eh Sea 4| 91.9) 72.7) 69.2| 66.4! 92.5) 81.7} 83.4) 81. 2) 69.0] 57. 5) 58. 5} 49.5 TES aie os aes CO Lovaas ae es a 6| 99.2) 88.9) 90.2! 89.3) 100.0) 93. 2) 94.1) 93.3] 94. 6) 88.7} 89. 2) 86.9 TAGS jes ht i ai ace 1-15} 92.9] 65.6) 69.1) 66.3) 65.0) 29.7} 39.1) 31.1) 41. 2) 38. 0} 38.3) 24.9 Fs) eh | PO A een neg Ses 1-15} 93.8] 56.5) 63.6] 60.3] 74.8) 36.8) 45.1] 37.9} 73. 2) 73.0] 73.0) 67. 2 21____| Lime-sulphur_-__- —7| 26.0) 6.7) 11.2) 3.1) 45.4) 18.6) 27.9) 18. 4] 61. 2} 41.3] 43.0! 30.7 22____| Unsprayed check-|____--_-_- WEP (a) es tated =o a 14. 0} 10. 8} 11. 6)_--__- Dos Allie Slee | eae Dareeen| AO Wipe aa et es 1-15} 27.7} 10.3) 14.1) 9.7) 46.4) 15.3) 23.0} 17.0) 46. 5| 41.4) 42. 6) 29. 4 DAR AOU G See oe aie re 4| 77.3} 44.0) 50.2) 47.6] 58.6) 22.6) 31. 6} 26.3) 73.1) 57.1] 61.6) 52.8 Dayoan ete GOS ae ikeset Seiad 4| 72.9} 28.9] 41.8] 38.8] 67.8] 22.8] 36. 5} 31.6) 60.6) 59.0) 59.4) 50.1 26_.__| Unsprayed check_|_______- PS Beno eb Olli eh Cees WAS Tk AN Ge PA Poy ay ls UN SG 7A Diet| MOTI G FS dee ea (Gy EGY ire fs 8S 9 ee We ESS 8 Ua et eat ae 96. 1) 97. 4| 97. 2) 96.6 1 For characteristics of oils used, see table 6. 2 Tests 1-22, inclusive, in orchard no. 1, the spray applied with a hand-pumped barrel sprayer. ‘Tests 23-27 in orchard no. 2, the spray applied with a power sprayer. 3 Emulsified according to formula no. 1 (p. 17). 4 Emulsified according to formula no. 2 (p. 17). In the tests reported in table 1 some injury resulted to the trees that were sprayed in the first orchard, this injury being confined for the most part to those tests in which the lubricating-oil emulsions were applied at the 6-percent dilution. It was most serious in the December application, less serious in the February application, and absent in the March-April application, There was no noticeable AZ CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE difference in the degree of injury caused by the three oils that were used, each oil causing about the same injury at the 6-pereent dilution. A few of the trees sprayed with the lubricating oils at the 4-percent dilution showed a few injured twigs (as evidenced by delayed bud opening), but in no case was the injury extensive or serious. Except from the 6-percent oil dilution in the December application, none of the injury was as much as would result from permitting a moderate or heavier infestation of the obscure scale to develop unimpeded. As the only really serious injury occurred as a result of the early December application, it was attributed to the fact that the trees | had not become fully dormant, with the added possibility that the condition of the trees may have been partially responsible owing to the fact that they had suffered considerably from drought during the preceding summer and early fall with subsequent premature defoliation. The liquid lime-sulphur and the miscible oils caused no injury in the tests in which they were used. Experiments were carried out during the dormant season of 1931-32 for the purpose of obtaining further information concerning the effect of oils of different physical characteristics on pecan trees and their effectiveness in controlling the obscure scale. The tests were applied with a power sprayer in a number of orchards offering varied con- ditions; some of the orchards were planted in bottom land, some in hill soil, some were intercropped, some were maintained in clean cultivation, some were healthy and vigorous, while others were growing under unfavorable conditions. Data showing the effective- ness of the materials used in these tests are given in tables 2 and 3, and data indicating their effect on the trees are given in table 4. TaBLE 2.—Results of spraying experiments on the obscure scale on pecan trees. Shreveport, La., 1932 [Approximately 1,000 scales were examined in each test except in check test no. 25, in which 2,000 were examined. Tests nos. 1-25, inclusive, were in one orchard and tests nos. 26-29, inclusive, were in a second orchard] | | Peers en Dilu| Seuest Gok Test ; . ilu-| Seales | tro est - ilu- es | tro no. Material used |tion!} dead ob- no. Material used tion!; dead ob- | tained ijtained ee ee Se Een een Per- | Per- Per- Per-| Per- | Per- cent cent cent cent cent cent 1 Game eat Qh 722 3 lent RIES 4 77. 05 68.275 | S16 ee: “|. OL Gee See ee 5 90. 10 86.5 Din eS ee Se GOs se S80 Be sel sak Daler 9756 aes Os4s | eel eee do. eee 6: |. 92a 90. 0 3 een {Leah (6 (cA ED Eoeialin 6 98. 54 9850 | ||S1S S22" Obi See ae ee 4 81. 32 74. 5 cy Ses ea! dS eRe ees 8 | 95.87 G4. 4) SEO Seen eee Ct Gnesi Sl = 87. O40 aRer3 (Feel ees Oils see er eee AS PSSeO Cale ade toe | eee dos Sea es 6| 97.83 | 97.0 (eee Nel CA dO a ee Sule Sbe7Onle 80: 532i OTOP sae eee 4} 58.10] 42.8 [fees 6 Va eee ES SR ee Gl 2962S fale 95:05) |e2 2s pee Oi 2 ee ee 5 | 83.10| 76.9 (3 a fe OT ES Gs ee See eee a Aci; (S6525n Ol. 23||\425= [ae do 23222 teh See 6| 91.70] 88.7 tt eerie Eee aa CON Re = ee Dil COC Sm lee. Onl ecaee eee dort2 eae 8 | 98.46 | 97.9 OQ See| Fars Gods Serie ees 6} 97.90} 97.1 || 25__-_| Unsprayed check_-_--_|_---_- 26 400 1 fy bet 8 Mea Se COE ite ad” > 8 | 98.64 | 98.1 || 26____| GS OS Pee 4} 80221) = F205 (Aare TE OT lis IGE or ee eR 4S) Oona OO: Onl laa tae ee dO Se22 5 = ee 5] 85.81] 80.3 US SES | eto Dp oe a Le eens 5 a 2A Dal ee ROG | lees eee GOS ere ee 6| 92.47; 89.5 iF A | ee en 0 (0 ae en ee, ees 6| 98.53} 98.0 || 29___.| Unsprayed check_-__-__|___-_- 21.974 PF EES MOT: Gees as ce oun ee 4| 63.97] 50.8 1 Percentage oil in the dilute emulsion. 2 For characteristics of oils used, see table 6, p. 18. 3 All oils emulsified according to formula no, 2, p, 17. OBSCURE SCALE ON THE PECAN AND ITS CONTROL 13 TABLE 3.—Average effectiveness of all oil dilutions used, as indicated by data in table 2, in spraying experiments on the obscure scale on pecan trees, Shreveport, La., 1982. Average Average Percentage of oil in spray Tests |\degree of Percentage of oil in spray Tests | degree of control control Number | Percent Number | Percent Fhe se es a GOR8 |: |G ee eee ee 8 94, 2 See ee: AS eee eee 8 S652.) Sis eee See ae ee 3 96. 8 TABLE 4.—Effect of oil sprays on dormant pecan trees, Shreveport, La., 1932 Effect of oils on trees to which applied Bottom-land orchards Hill-land orchards Planted in alfalfa, Cropped with Oil Dilu- soil fertile, twig | Tree rows clean | cotton, soil poor, : : ) tion growth moderate, | cultivated, soil | twig growth light} Clean cultivation in summer, nO.) used foliage good until | fertilized, twig | to moderate, fo- winter cover crop planted but affected by | growth strong, liage fair until died out, soil poor, eroded, twig drought late in | foliage excellent; affected by growth light, foliage poor; trees fall 1931; trees as | trees unusually | drought early in lacking in vigor. Sprayed Feb. a whole moder- |vigorous. Sprayed] fall of 1931; trees 24 ately vigorous. Mar. 2 fairly vigorous. Sprayed Feb. 29 Sprayed Feb. 12 Percent 17 AD IN ONG we esates ee at Ss eal ae None ese: Eyl eee CGY yh a els Ne al (Pe ec RTA Ce Men cee ioe Gels CO Kaye etek Bienes (ES So Noneiaes bars 14 Ae sees CGY ei ae SSS Se 8 a Os cere ae Ee | ee Lee ER SSNS |e ns RE Pee pec | I Ol 0)5 is Re @ oes CY) 5 A ses May Eo | (RRR RN A ey a es Coby 2 Sabie 16 AG Berean 6 KG) Se SS lo Re doe kas Light, twig tips injured. Fa | AD RES re) eee a el es eae Ee Gots ales: (Hyllsaee OE Se ee as oe aera See Light, 2 small | Moderate, 4-5 small-medium limbs serious- limbs killed. ly injured. SS eS a ea an aS Re a er SLE Severe, 30-40 percent limbs killed. TU Ye se 2S (I a aia Severe, 50-60 percent limbs killed. 15 Asal BIN) TAQ Woe ee = caste aA mag lace el INO GH ais hee Light, 3-4 small limbs hurt. Lap ees (6 0) Spa 5 ih ac MO a coi RR GOmEs ee Cay) fail Dy 2K eYe eek ee SA | BR Crema OS 2 ae oe ee Traces ios. Sian Moderate, 4-5 small-medium limbs killed. FN | Fes ge ce MRRP ce SE ama | Ree SM Soy DL About same as 6 percent dilution. SS | aa ri So Mc Shee A | nt a ye aL ae iA SR IC Severe, about 70 percent limbs injured. 6 Ala tN ONO eke eae 5 ae ek INONeSeteies ss INONGu as ee oes EF) WD ga CCS ss Se SS oe OME rege a ek, Qe ee wee Bh NIOMO Lee us sie SER Koy Soe ae PRT ACO D vacies 18 Ase | el ap eee UU cau a UL A INGO) ae ee Trace, a few twig tips hurt. ya eee (ite el gene a age Og (gs ra pee Ge Piaohitee 22-3 astray | Sees eee tte Moderate, con- | Light, 2-3 small limbs made weak limbs killed. siderable weak growth. sickly foliage. pS) | aR eR IT ec | Pol we ee UY Ue ee dec Light, retarded bud opening, 1 medium sized limb killed. Dt Sa ee ae NS Ee eee ee Ue SP Ba! ee Pd ea eee Severe, 50-60 percent of tree seri- ously injured. 19 AAIWIN ONG Gates e eae 2e Sein? SRS INOne! 222-2 See Light, twig tips injured, 1 small limb made poor growth. Sel eee CK et PP a I ae re GLA 8 CG Ko eeies joc GND Gill Cem arte teeg 8 fe Eee A oo 2 ER tare dol Bai Moderate, some dead twig tips, 4-5 small limbs killed. Poh A ages al cas ee Sl eee eae Sg cee ays pa a Severe, 20 percent of tree seriously injured. (26 |e ee een eee ok | AE Dee Se Oh RS Severe, 50-60 percent of tree seri- ously injured. The data in tables 2 and 3 indicate that it is an extremely difficult task to obtain a 100 percent kill of the obscure scale, three tests in which 8 percent lubricating-oil emulsions were used failing to give such a kill. At the same time, these and other tests (table 4) showed this strength of oil unsafe for application to dormant pecan trees. The data furnish, to a large degree, the answer to the problem as to 14 CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE what dilution of oil will give the best control with a reasonable degree of safety to the trees. As in previous tests, 4 percent oil sprays gave a good control of the scales developing unprotected by old scale covers whereas they gave only a fair degree of control of those beneath the old covers. At the same time they did not injure dormant pecan trees in the tests in which they were used. Sprays containing 5 percent of oil, not pre- viously tested, gave a decided increase in the percentage of control (table 3) over those containing 4 percent, but they were slightly more dangerous to use (table 4), indicating that they should not be recom- mended for use without some reservations. As in previous tests, sprays containing 6 percent of oil gave a reasonably satisfactory con- trol of both light and heavily encrusted infestations and proved the most satisf actory ones to use from the standpoint of control obtained, but, as in the previous year, they caused no injury in some and serious injury in other instances. For this reason, this strength cannot be recommended for use. It should be noted that oils of very low vis- cosity (oils 14 and 17, table 6) were practically as effective as those of higher viscosity and ‘caused less injury (table 4) to the trees in the orchards in which they were tested. It is desirable that these oils be tested further before they are recommended for general use. With the exception of oil 19, which gave somewhat lower results than other oils, there were no consistent differences in the percentage of control given by the oils used in tests reported on in table 2. This indicates that, in general, oils having the physical characteristics of those usually recommended for use in dormant oil sprays will prove to be about equally satisfactory from the standpoint of scale control, with the added possibility, as previously mentioned, that oils lower in viscosity and higher in volatility (oils 14 and 17, table 6) may prove effective and safer. The data in table 4 indicate that pecan trees are unable to with- stand as strong concentrations of oil sprays as are many other decidu- ous trees. The injury which in some cases did result did not vary in degree according to the viscosity, volatility, or unsulphonated residue of the oils used, although some oils (16 and 18) appeared slightly more likely to cause injury than others. Also, oils which caused injury in one orchard were used with perfect safety i in others, and vice versa. Therefore it seems likely that some condition or factor other than the oils limits or controls the quantity of oils that pecan trees are able to stand without suffering injury. Tests not listed in table 4, in which oils 15 and 16 were applied to young, vigor- ous trees on the laboratory grounds at dilutions as high as 25 percent of oil, showed that no injury resulted when the applications were made during the strictly dormant period and but little injury when they were made at the delayed- dormant period. In other tests, oils 18 and 19 caused no injury when applied at a dilution containing 3 percent of.oil during the dormant period, but when they were applied at the delayed-dormant period they caused injury in some, but not all, instances to the extent of setting back bud opening and develop- ment for 4 or 5 days. This setback was soon overcome and appar- ently no permanent injury resulted. Even so, it is evident that the application of dormant types and strengths of oil sprays should be confined to the strictly dormant period. OBSCURE SCALE ON THE PECAN AND ITS CONTROL 15 From observations made by the writer it would appear that one factor more than all others likely to determine whether injury will result from the application of dormant oil sprays to pecan trees is the physical condition of the trees themselves. Strong, healthy, vigorous trees enjoying the benefits of good soil, cultivation, fertiliza- tion, moisture, and healthy foliage apparently withstand heavier dosages of oil sprays than trees growing in poor, unfertile, uncultivated, unfertilized, or eroded soil and suffering from drought or premature defoliation. SUMMER SPRAY APPLICATIONS In addition to the attempts that have been made to secure control of the obscure scale by means of dormant spray applications, addi- tional efforts have been made to limit its spread and development by the use of summer applications of oil sprays. During the emergence period of the crawlers in 1931 and again during the same period of 1932, tests were made to determine whether the application of oil sprays to the trees would prevent or deter the crawlers from settling, or, permitting them to settle, perhaps prevent or interfere with their normal development. In 1931, oils 1, 6, 11, 12, and 13 (table 6) were emulsified according to formula no. 2, page 17, and applied to good-sized limbs on orchard trees at dilutions of 0.5, 1, and 2 percent of oil by means of a com- pressed-air sprayer. Oils 8, 9, and 10, commercially prepared sum- mer oils, were applied in the same manner at dilutions of 1 and 2 percent of oil. At regular intervals twigs were cut from the sprayed limbs and taken to the laboratory, and crawlers were transferred to them as long as the oil seemed to affect the settling of the crawlers. The high-viscosity low-volatility oils exerted the more pronounced and most lasting influence on the settling of the crawlers, the degree of and duration of the influence being directly proportional to the strength of oil used. The dormant-type oils caused foliage injury when used at dilutions exerting any pronounced deterring influence on the settling of the crawlers. The summer oils caused no injury. Oil 9 at 2-percent and oil 10 at 1-percent dilution exerted a pronounced deterring influence on the settling of crawlers for a 3-day period, ae oil 10 at 2 percent exerted a strong influence over a period of 2 weeks. In 1932, oils 8, 9, 10, and 20 were used in similar tests, except that potted trees were sprayed instead of orchard trees. Oil 20 was emulsified according to formula no. 2 (p.17). Two trees were sprayed with each oil at dilutions of 1 and 2 percent of oil, respectively, in the diluted emulsion. Crawlers were transferred to them at regular intervals as long as any of the oils appeared to be exerting any influ- ence on the settling of the insects. Oils 8, 9, and 10 showed no deterring influence after the third day whereas oil 20, much lower in volatility than any of the others, exerted a considerable influence at both the 1- and 2-percent dilutions for 2 weeks and some influence at 2 percent for a slightly longer period. About 1 month after the final transfer of crawlers those specimens successfully settled on the oil-sprayed potted trees appeared to be developing just as normally and successfully as those settled on unsprayed check trees. The spraying of pecan trees infested with the obscure scale during the crawler-emergence period to kill the crawlers or prevent their settling is not deemed practical, for the following reasons; (1) The 16 CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE long period during which crawlers are present, (2) the relatively short period that any of the oils tested were effective in deterring crawlers from settling, (3) the comparatively high cost of oils of an effective and safe type, (4) the fact that those crawlers eventually settling are able to develop as normally and successfully as if on unsprayed surfaces, (5) the difficulty of obtaining a thorough covering of infested trees, and (6) because the cost of the treatment would be out of all proportion to the benefit resulting. As the writer believed that the newly settled scales might be more readily killed than older, larger ones, oil sprays were applied to heavily infested branches by means of a hand-operated compressed- air sprayer in the summer of 1931 after the height of crawler emer- gence and settling had passed. These tests and the results effected by them are given in table 5. TABLE 5.—Effect of oil sprays on newly setiled young of the obscure scale on pecan trees, Shreveport, La., 1931 Seales settled Seales dead Test : ——— SS | RL Ce : Oil used 1 con- Effect on foliage 05 tent Pro- Ex- Pro- Ex- dead trol 5 tected | posed | tected | posed Num- | Num- Percent| ber ber Percent| Percent) Percent| Percent f Ieee Bakelite ey es oet ome. a 1.0 676 325 | 21.89 | 34.15] 25.87 | Minus | None. TOROS) eae Gp rsa S ery 2.0 622 386 | 26.05 | 49.74) 35.12 10.6 | None. Sy ad OQneraaae? Aa eee 1.0 631 369 | 23.93 | 48.78 | 33.10 7.8 | None. Ap seat eee Ap aie ae Sea es 2.0 625 381°] 26.24] 51.71] 35.88 11.7 | None. Ayre. ok cA Sees eh ge ee na 1.0 729 Zi2)| 22591} 52.50 | 30287 4.9 | None. Ghote Se Qe ees 2:0 758 242} 34.43] 71.07} 43.30 21.9 | None. “(eee TE ieee oe eee oe & ay 687 313 | 25.47 | 45.69] 31.80 6.1 | None. slot eas |e Te CC Cees ae A eae 1.0 835 175 | 21.20} 37.14) 23.96 | Minus |} None. AT he SE gee, (IGE Seas Shee 2.0 787 219 | 37.48) 71.69 | 44.93 24.1 | Small amount. AQ EA! Se Sak A es 5 722 281 | 28.67 | 55.16] 36.09 12.0 | None. [flee eee Gps ae Saas: 1.0 806 227 | 29.16) 76.65] 39.59 16.8 | None. i Lees | maa Go 22 Se 2.0 791 209 | 54.61} 99.04} 63.90 50.3 | Small amount. Sete gay. eae ae a eg =a 659 341 | 24.89]; 52.20] 34.20 9.4 | None. iF Gages (eee eee 1.0 7 214 |; 23.22) 56.07 | 30.24 3.9 | None. eer oat Gol sheen tS oes 2.0 844 162'| 48.58 |. 92.59) } 55. 67 38.9 | Small amount. dG 2225) Unsprayed check_-_|_______- 750 250; 21.73]. 44.40} 27.40 |_..---=- | | | | 1 For physical characteristics of oils used, see table 6, p. 18. 2 Oils 8, 9, and 10 were commercially prepared summer oils. 3 Oils 11, 12, and 13 were emulsified according to formula no. 2, p. 17. None of the tests shown in table 5 gave any worth-while control, test 12 giving the best, namely 50.28 percent. As with the dormant- spray applications, better control was effected of the exposed scales than of those developing beneath old covers. This again indicates the inability of oil sprays of low dilutions to penetrate these old scale covers sufficiently to effect a high kill. In addition, those oils giving the best control showed a tendency to cause some injury to the foliage, indicating that they could not be applied to the trees with any wide margin of safety. RECOMMENDATIONS FOR CONTROL As a result of the data presented in tables 1 to 5, inclusive, together with supporting data, the following recommendations for effecting control of the obscure scale on pecan trees are presented: (1) If the infestation is light (not heavily encrusted), use a 4-percent lubri- cating-oil emulsion regardless of the physical condition of the trees. (2) If the infestation is heavy, use a 4-percent lubricating-oil emulsion OBSCURE SCALE ON THE PECAN AND ITS CONTROL 17 if the trees are in poor physical condition and a 5-percent emulsion if the trees are in otherwise good physical condition. (3) Make all applications during the strictly dormant period, but preferably not until after the first of January, in order to give the trees plenty of time in which to become dormant. (4) Apply the spray to all portions of heavily infested small to moderate sized trees and to the lower three fourths of all other trees, making sure that the application to the parts sprayed is thorough, remembering that the scale specimens must be hit by the spray to be killed by it, but do not drench the parts sprayed beyond the point necessary to obtain a complete coverage. (5) Use any oil within the range of the physical characteristics usually recommended for use in dormant oil sprays. The usual oils appear to be about equally effective and to offer about the same margin of safety to the trees, with the added, though not yet thoroughly tested, possibility that oils lower in viscosity and higher in volatility than those generally recommended may prove effective at strong dilutions and give a wider margin of safety to the trees. FORMULAS USED IN PREPARING LUBRICATING-OIL EMULSIONS The formulas used in preparing the lubricating-oil emulsions employed in the tests reported upon in this circular are given below. For more complete information regarding the preparation and use of oil sprays, the reader is referred to Farmers’ Bulletin 1676 (8). No. 1.—Lubricating-oil emulsion (soap emulsifier). Made according to the standard Government formula (1) (Oe i ae mp ea at i eg Gap 2 gallons. Wie Ge Teee =. Ti