ST^TK .T^?BO..»» E-506 U.S. DER\RTMENT AGRICULTURE BUREAU OF tNTOMOLOGY AND PLANT QUARANTINE July 1940 I1JV3STIG-ATI01IS IN COiTTHOL 01? HEl-JPTEHOUS COTTON INSECTS IN ARIZONA BY TES USE OP I^TSECTICIDES By T. P. Cassidy and T. C. Barter, DiV/ision of Cotton Insect Investigations^'' Introduction The problem of reducing the damage caused to cotton hy hemipterous insects in Arizona has "been ^receiving serioiis consideration during recent years. In 1938 a circular^/ vjas issued hy the Bureau of Entomology and Plant Q,uarantine giving the progress of experimental work up to and includ- ing the season of 1937, That circular described the methods v;hich had been followed in determining the relative economic importance of each species to the cotton crop, discussed the more economical3.y important species, and included a description of the character of the damage inflicted to the cot- ton plant by the different groups of insects. It concluded with a resume of the experiments in control vdth insecticides, which had been conducted to that time, together vriLth recommendations of measures which had been in- dicated as practical and profitable as a result of these experiments. Since Circular E-439 was published, 2 more shears of experimental control work have largely confirmed the correctness of the information given therein. The present circular is intended to supplement the earlier one by reporting the results of 2 more years of experiments, including, last season, the use of airplane dusting. -he More Important Hemipterous Insects Attacking Cotton in Arizona Out of 53 species of hemipterous insects collected on cotton in Arizona, 8 v:ere listed in Circular E-439 as being those most injurious to l/ The v;riters v;ere assisted in the field ^o:r !f. A. Stevenson, H. &, Johnston, L, W. Sheets, J. I-I. Breazeale, and H. J. Crawford. 2/ Cassidy, T, P., and Barber, T. C. Hemipterous Cotton Insects of Arizona and Their Economic Importance ajid Control, U. S. Dept. Agr., Bur. Ent. and Plant Q^ar. Circ. E-439, (iiimeographed, ) the cotton crop. These included three pentatomids, Suschistus impictiven - tris Stc.l, Chlorochroa sayi Stal, and Thyanta custator Kirk.; four nirids, Lygus hesperus ICnight, Lyg:as -jpratensis o"blineatus (Say), Creontiades f emor- alis Van D,, and Psallus seriatus (Heut.) ; and one pyrrhocorid, Dysdercus min:ulus Hussey. A cliange has occurred during the past 2 years in the importance of Dysdercus ..daulus . ?or some unknovm reason this species, which v;as then abuixo-ant , has become so scarce, especially in the Salt Idver Valley, that amons collections at thousands of points in 1939 only two or three speci- mens v/ere found. VJhile this insect v;as so scarce that it was not consider- ed of much economic importance in 1939, it must he recognized that at any time it may reappear in damaging numbers. -he increasing importance of the mirid Creontiades femoralis should also he emphasized. This species is ap-oarently increasing in the ma.in Arizona cotton areas, particiilarly in the south side of the Salt Pdver Val- ley, v:here for the past 2 years it has greatl:-- outnumbered the combined po- pulations oi :he two species of Lygus, which v;ere formerly considered the most common and destructive mirids. Repeated experiments have proved C. femora.lis to be more destructive to the cotton plants, insect for insect, than either of the species of Lygus . I-.'oreover, Creontig.des can maintain itself and multiply readily on the cotton plants throughout the grov;ing season, vmereas Lygus can maintain itself in the cotton fields only after the plants have become large enough to furnish heav?'- shade and are squaring and fruiting heavily. Even then it does not multiply rapidly on cotton, and Liost of the population comes from migrations fron other host plants in the vicinity. \Iith. the foregoing modifications the original list of the more in- jurious heraipterons in Arizona cotton fields is still accurate. No new hemipterous insects of marked economic importsjice to the cotton crop have been found in Arizona during the past tvro seasons. ITature of Dajnage to Cotton by Pentatomids (Stink Bugs) The three important species of stink bugs in Arizona cotton fields are boll feeders, and feed but little on either the foliage or squares. The damage caused by boll puncturing is greatly aggravated by lint stain- ing, v.'hich follows as a result of pathogenic organisms that gain entrance to the bolls through the \umctures. Punctured bolls are shed in large num- bers, but the ones not thrown off maj"- exhibit varying degrees of injury from a small stain in ono lock of the matured boll to what is termed an "unpick- able boll," v;hich is a mu,uaified, half-opened boll with the lint in every lock impacted, stained, short, weak, and of little or no market value. In heavily infested fields a high percentage of the bolls are unpickable and remain on the plants after the crop has been picked, and in extreme cases the yield may be reduced by more than one-half. Nature of Damage to Cotton by ilirids (Leaf Bugs) The damage caused to cotton by Lygus sp'D., Creontiades femoralis . and other mirids differs from that of the pentatomids in that it is mainly - 3 - concentrated upon the terminal bi-'ds, squares, and small "bolls. The bud in- juries frequently result in a deforaed vegetative tyT.De of grov;th, due to ex- cessive "branching of adventitious "buds following the destruction of the terminal buds, Tlie square in juts'- causes heavy shedding resulting in a re- duction of the ultimate crop, although the squares shed are partially com- pensated for by the tendency of the cotton plant to put on extra fruit to replace early losses. Damage is also inflicted on small bolls, resulting in considerable shedding and light lint staining, but the boll damage is much less severe than in the case of the pentatomids, and the staining is not so pronounced. Although the vrork of the mirids is not so conspicuous as that of the pentatomids, the total, amount of loss will closely approach, if not exceed, that caused by the stink bugs. Indirect Loss from Hemipterous Insect Damage In addition to the direct injurj'- to the cotton, a secondary source of trouble consists of the dissatisfaction among the cotton pickers in fields which have been heavily damaged by hemipterous insects. The cause of the trouble is the sticking of the lint to the proliff^rations within the punctured bolls, augmented by the tendency of ''odi-- p'lnctured bolls to open only partially, so that undue effort is required to pick the cotton from them. These punctured bolls often require several, "pulls," while in a clean, unpunctured boll the lint can usually be gathered mth a single motion of the hand. Since in damaged fields the arao\mt of cotton a picker can gather is determined largely by the percentage of punctured bolls, the pay is correspondingly reduced. This aspect sometimes assumes serious pro- portions, the pickers migrating from camp to camp in an effort to locate "clean" cotton fields. The effect of hemipterous insect injury upon the Arizona cotton crop was summarized in Circular o-439 as follows: "(l) It reduces the total amount of the crop by causing abnormal cotton plants and heavy shedding of the squares and small bolls. "(2) It reduces the grade and value of the lint on account of the staining which follows the attacks of the boll-feeding species. "(3) In Cases of heavy infestation it renders a certain percentage of the crop 'unpickable' and valueless through the almost complete destruct- ion of many bolls, "(4) It reduces the value of the seed for planting or milling, as many seeds are injured in early development and fail to mature. J.'any of the faulty seeds are also broken in ginning and become mixed with the lint. '^(5) It Causes much dissatisfaction among the cotton pickers by- slowing down their work and hence reducing their pay." - 4 - Extent of Damage to Cotton "by Hemipterous Insects in Arizona Accurate estimates o juries are more difficult t on the daraa.^e inflicted "by 1934 to 1939, inlcusive, an cotton-gro'^c n.3 areas of Ari in all there areas, and cot field. Mail/ olioj.ocn.ds of c which vere 'bnu^lii: into the ternally and internally. A is shown in table 1. f the losses from Imd, square, and small "boll in- ohtain, hut much information has "been secured hemipterous insects upon the mature bolls. From intensive survey vras made each fall of the main zon.?.. Representative cotton fields v/ere selected ton hojla v/o:.*e cclJ.ectPd fr.-^n live points in each ottcn lolls vrere th-.is colleci-e.d each year, all of laboratory and e.xaminod indjvidually, both ex- summary of the results of these annual surveys Table 1. — Damage to cotton boll s by hemipt erous insects in Arizona cotton areas, 1934 to 1939, inclusive Year Short - -staple cotton Lonf -naol e cotton Number oi Percentage Number Percentage bolls of bolls of bolls of bolls examined punc tured examined p\inctured 1934 18,393 23.4 __ „_ 1935 30,700 27.2 1936 41,500 24.8 12,500 6.15 1937 21,200 23.5 5,000 7.7 195' 43,810 31.5 30,958 14.63 1939 35,000 28.2 27,500 8.73 Total 190,603 75,958 Average 26.3 9.29 These figures show that over a period of 6 years an average of 26.3 percent of the short-staple bolls for the State had been punctured by hemip- terous insects. In long-staple cotton the damage ^oy boll-feeding insects is materially less, tut considerable evidence has been gathered to indicate that tne bud and square injury is probably as ;^reat as if not greater than in the short-sxaple cotton. The comparative amount of boll injury varies greatly, yet consistently, with the locality. ?or 6 consecutive years Ytusa County, in the southwestern corner of the State, has shovm the heaviest hemipterous insect injury, ranging from 40.3 percent in 1937 to 62.1 percent in 1939, '-'ith a 6-year average of 53^7 percent. Pima County has as consistently sho'-m the least injury, rang- ing from 5.1 to 12.2 percent, with a 6-year average of 7.4 percent. The re- maining cotton-producing counties have always fallen between these two ex- tremes of infestation. A number of factors are resoonsible for the differences in the amount of damage in different sections of the State, some of them unicnovm. The boll-puncturing species are general feeders and attack many fruits and seeds, •■^hey are frequently abundant in damaging numbers on other crops, such as al- falfa, sugar beets, and grain sorghioms, and they are found in considerable ■ - 5 - numbers on desert vegetation. The infestation in cotton is mainly due to their migrations from these alternat--5 host plants. The proportion of land planted in other crops and their proximity to the cotton fields, the time they are harvested, the amount of rain and its effect on desert vegetation, and the density of weed growth and other vegetation, all influence the mi- grations of hemipterous insects to cotton and the time when damage occurs. Control Experiments After preliminary tests with various insecticides in lantern glohes and cages, small field plots were dusted with hand guns and then larger plots of 2 to 5 acres were dusted with a five-roiir pov/er duster. For the past 2 years particular attention has "been given to sulfur and combinations of sulfur and paris green or sulfur and calcium arsenate. The increase in yields over the checks in the 53 plot experiments conducted during the period 1933 to 1939 are given by years for each locality in table 2 and are sum- marized in table 3. w C rH O § ^ Sh a) " P< Q) •H N c: •H d QJ ^ iH rf w O w CO o 0) 4-5 o rH d O U o +3 > rt •H O tt-H o xi o rH Q) M 4-3 ^ rt G) £ rH •H d ;h o (U ! ^ - 6 - r^ Oj| r^ CD o K> ct3 CO d to C\J| O rH O rH pq d r— o O rH O O t^ ^- pq O rH t^ en it w ^l^ rv-l d o •H ,H W O ,J -H rH CO ^ ci d o p^ o 8 } o rH rH C^ I r— -J- 1 ^.o I 0~N TO I J- C\J t^ rt o o O 4J feS W CO •H f., f4 d d PL. ri f-i ;:( o d rH CO '♦H u d •H y C3 O •H d '^ o -^ o to f-^ o bO TO I CM r^ r--\ 1 1-r. 1 rH r-\ c^^ 1 --rf r- TO r-\ I TO 1 Lr\ rH OJ !I^ I rH ^ >jr\ r-'^ rH f'V rH O rH r-i cr\ d 'g- ^ TO I 1 ^ 3 pi ^ rH •. ^ ■^'i. to O cv o . 4-> rH o M fl !h O d O r-i U ■ d d J I ^-' • r-\ r-i fH O^ tH 0> I& -1^ d I \,^ o M PJ CJ U C) o d o o O .H -H rH !h J-i d d d r-n rv-J in 7 - Table 3 — Average gains from the use of different insecticides tested upon a field-plot basis in Arizona, 1933 to 1939, inclusive Insecticide tested Calcium arsenate and sulfur Paris green and sulfur Sulfur Paris -ireen and calcium arsenate Lead arsenate Calcium arsenate Sodium fluosilicate Pyrethrum Derris Derris and sulfur Pyrethrum and sulfiir Paris ,^reen 7-1/:j1, clay 92-l/2^: — ' In most experiments the treatments were replicated from one to several times, and the mimber of plots treated is therefore much greater than the n\amber of experiments shoiim. Total of ex ments number Average gain in seed cotton, pounds jjer acre. 8 683.2 10 528.6 11 525.2 S 392.0 7 329.1 5 258.4 2 258.5 2 233.0 2 144.5 1 151.0 1 41.0 1 19.0 - 8 - It will be noted that the first three insecticides listed have shown the largest gains year after year; these i'ains fluctuated greatly in different localities and years, as they were affected by local condi- tions and the intensity of insect ponulations. The calcium arsenate-sul- fur mixtures in 8 experiments over a period of 4 years and in 3 localities have given an average gain of 683.2 pounds of seed cotton per acre over un- treated check plots. The paris green-sulfur mixtures in 10 experiments over a period of 5 years in 3 localities have given an average gain of 528.6 pounds of seed cotton per acre. Dusting sulfur in 11 exoeriments over a period of 7 years and in 3 localities has given an averaa:e gain of 525.2 pounds of seed cotton per acre. In addition to giving the best in- sect control of all treatments tested, these three insecticides are avail- able at a reasonable cost. Airplane Cotton Dusting Experiments in Arizona, 1939 In the experiments reported above, the insecticides were applied with hand dust guns and ground -oower diisting machines. However, neither method of application if fully adapted for large-scale field dusting in Arizona. The hand machines are too small to be practical and require too much expenditure for labor, '-.'hile a po^'-er dusting machine can efficiently dust some 50 or more acres of cotton in a night at an application cost of about one-half of airplane dusting, the use of pov/er eround machines pre- sents definite difficulties. The irrigation schedules interfere seriously '.^rith the use of a ground duster, as in some soils the machine cannot be used for several days after an irrigation on account of the muddy condition of the ground. I'/hen cotton reaches its maximum growth the latter oart of the season, insect loopulations have usually reached a peak and dusting is most urgently needed, but the dusting machine cannot be dra\\ni through the fields without causing material damage to the cotton plants and fruit. Then, too, in the event of a sudden insect migration to cotton, it may be necessary to apply insecticides at a much faster rate than can be done \^th a ground machine. For these reasons it is believed that hand and power machines vrill not be entirely suitable for average conditions in Arizona. Obviously a method of insecticide apt)lication is required which \i!ill not be affected by the field irrigation schedules, which v/ill not in- jure the cotton plants when they attain large size, and moreover \\rill oerrait the dusting of large acreages in the shortest possible time. The use of airplanes promises to meet these requirements. The desired tyr^e of dust cloud as applied with a ground povrer dusting machine is shown in Figure 1. It has been found that under ideal climatological conditions a satisfactory dust cloud and distribution of insecticides can be obtained Vfith airplanes in Arizona. An airolane dusting cotton is sho^m in '^igure 2. During 1939 a series of largo-scale airplane dusting experiments Tvas conducted cooperatively with the J. G. Boswell Company and a number of cot- ton growers to obtain information on the efficiency, practicability, and ex- pense involved in this method of insect control, and the minimum number of injurious heraiioterous insects that would justify airplane dustin;?;. The dis- tribution of dusted cotton fields was planned to cover the major cotton- growing sections of the State, and they included fields located in areas - 9 - that were heavily and lightly infested in previous years. The fields were selected and arrangements made for the cxpefiments before the insect ab\in- dancc could be determined. Later examinations showed that in some fields the insects did not reach what are considered to be commercially damaging populations, and in no fields v/ore the populations as heavy as in some of the previous experiments dusted v^ith ground machines. Fovever, as one of the aims of the airplane dusting experiment \^ras to determine the insect po- pulations that \\roul(i justify control operations and oroducc a profit, it was decided to carry through the season 8 large-scale field experiments as planned, regardless of insect populations or cost. Each field consisted of 40 or 80 acres, half of \irhich was dusted with a mixture of 7-l/2 percent paris green and 92-1^2 percent sulfur and half left as an untreated check, '■^he gains over the checks in the £ dusted fields in Maricopa Coujity in 1939 are shown in table 4. Table 4. — Summary of gains in the airplane dusting ex- periments, Salt River Valley, Arizona, 1939 Gains in seed cotton, dusted plots over checks Pounds per acre Percent 47 3.2 34 2.5 87 4.1 208 9.3 59 7.1. 242 40.4 154 12.5 240 15.7 Average 5 short-staple fields 123 6.9 Average 3 long-staple fields 152 20.0 It will be noted that despite the unfavorable insect conditions for the ex-periments. Increases in yields ranging from 2.5 percent to 40*4 per- cent vrere obtained. In the 5 §hort-staple fields an average gain of 123 pounds, or 6.9 percent, of seed O^ot ton per acre vras obtained by dusting, while in the 3 long- staple fields the average gain was 152 pounds, or 20 percent, of seed cotton. These figures and the seasonal insect population counts show that airplane dusting v;ith the paris green- sulfur mixture will reduct hemipterous insect populations and their injury to cotton but that it will not be profitable under all conditions with low insect populations. The population and yield records in the experimental fields of 1939 indicated that, while some increase in yields could be secured from dusting fields with light infestations, a population of 12 to 15 of the injurious species per 100 strokes ii^ith a standard sweep net is required to justify control by airplane, , and that dusting should be discontinued ^^fcen the in- sects are reduced below these numbers, further work is needed before de- finite recommendations can be made as to the t)opulations that vdll yield yield No. Location Type cotton 1 Palo Verde Short 2 Buckeye Do. 3 Perryville Do. 4 Marinette Do. 5 Marinette Pima 6 Chandler Do. 7 n-ilbert Do. a Meoa Short - 10 - profitable returns from control, the increase in yields that can he expected, and the number of dust applications that will give the most economical control, There have been so many requests for the results of the airplane dust- ing experiments that the detailed records of t^.'o fields, one in short-staple and one in long- staple cotton, are given in the following xDages. Seasonal Kistorj'- and Yield Records of :5xperimental Field No. 8, Acala Short-Staple Cotton This was an 80-acre field divided into four SO-acre strips, tv/o of which were dusted and two undusted for securing comparative records in the treated and untreated cotton. IXisting records: Insecticide applied — paris green 7 l/2^', sulfur 92 l/2-l, at 7-day intervals. Number of applications — 7, at 15 pounds per acre-application. Method of application — airplane in early morning hours. Dates of aoiDlication — July 13, 20, 26, August 2, 9, 16, 23. Cost of dusting — $1.17 per acre-application, including insecticide. Total amount of insecticide applied -«- 4,200 pounds Hemipterous insect infestation records; Twelve population counts made at vreekly intervals. First count made June 22 and final count made September 8. Populations of injurious hemioterous insects; !?umber of in,jurious insects per 100 strokes Dusted Check Seasonal average Peak infestations Period of commercial damage Dusting reduced the infestation an average of 2.04 injurious insects per 100 net strokes over the season, and reduced the peak infesta- tions by 9 insects per 100 strokes. It also reduced the period of severe damage by one-third. 8.21 10.25 19 28 3 weeks 4.5 weeks - 11 - Records of form counts: Average number of forms peri -plant Date Dusted Check June 23 9.77 9.33 July 19 32.08 27.69 August 26 17.85(15.88 bolls) 13.96(13. 27 bolls) At the last count, the dusted plots exceeded the check plots on the average by 2.61 bolls per plant. Record of boll examinations for hemipterous insect damage: Percent of bolls punctured Date Dusted Check August 10 21.75 31.25 September 6 34.25 52.00 Yield of seed cotton in comparable areas; The avera£:e yield per acre was 1,770 pounds in the dusted plots and 1,530 pounds in the check plots. The average gain in the dusted plots over the checks was 240 pounds, or 15.7 percent. Rendition of lint: On a field basis the gin records shov; that the dusted plots yielded 0.8 percent more lint from seed cotton than did the check plots. 12 - Classing an d grading records: Dusted Check No. of bales Percent Ho. of bal es Percent Total yield 47 -- 39 — Grade V • .Strict H iddling 23 48.9 8 20.5 Middling 24 51.1 31 79.5 Color ^■Tiite 44 93.6 36 92.3 Spotted [last picking) 3 6.4 3 7.7 Staple 7/8" 2 4.3 2 5.1 15/16" 3 6.4 6 15.4 1" 14 29.8 16 41.0 1-1/32" 24 51.0 10 25.7 1-1 '16" 4 8.5 5 12.8 It is seen that a higher percentage of lint was produced and a het- ter grade and staple was obtained in the dusted cotton. Value of Acala seed cotton V.'ith a gin lint turn-out of 36.5 percent, 9.5 cents per pound for the lint and "^24 per ton for the seed, 100 potinds of seed cotton v;ould bring the following raturns; 36.5 pounds of lint at '^0.095 ^3.47 63.5 pounds of seed at <^0.012 0.76 Total !^4.23 - 13 - From the extra yield gttrioutable to dusting, however, the follow- ing costs per hundred pounds of seed cotton would have to be deducted; Picking and hauling .=^0.95 Ginning 0.30 "lagging and ties 0.09 Total $1.34 he net value of 100 pounds of \cala seed cotton would therefore "be !^4.23 minus ''1.34, or $2*89 per hundred. Computing profit from the above figures, and not considering the increased value of the diTsted cotton due to an increase in lint turn-out and a better grade and staple, the value of 240 pounds of seed cotton gained per acre as a resu-lt of dusting is $6.94. "^he cost of seven ap- •olications of dust at '^^l.l? per acre-application is $8.19, which shows a net loss of $1.25 per acre. Eox-zever, a.t least three applications of dust were made in the experiments before the insect population reached damaging numbers, and it is believed that four applications would have given the same yields and a profit of .^2.26 per acre. . Seasonal History and Yield Records of Exoerimental Field llo. 5, Long-Staple Cotton ""his was a 40-acre field of Pima cotton divided into four 10-acre strips, two of which were dusted and two untreated. The field was divid- ed into l-acre plots for securing yield records in the dusted and undust- ed cotton. Dusting records; Insecticide apT:)lied — paris green 7 1/2^, sulfur 92 l/2^ at 7-day intervals. ITumber of applications — 7, at 15 pounds per acre-apDlication. Method of application — airolane, in early morning hours. Dates of application — July 13, 20, 26 — Aug. 2, 9, 16, 23. Cost of dusting — $1.17 per acre-application, including insecti- cide Total amount of insecticide applied — 2,100 pounds. ^m^"^--^ - 14 - Hemipterous insect infestation records; Twelve population counts made at weekly intervals. 7irst count made June 22 and final count made September 8. Nxamber of injurious insects per 100 strokes Dusted Check Seasonal Average 14.25 20.10 Peak infestations 27 37 Period of severe damage 6 weeks 7 weeks Dusting reduced infestation an average of 5.85 injurious insects per 100 net strokes over the season, and reduced the peak infestations "by 10 insects per 100 strokes. It also reduced the period and intensity of severe damage. Records of form co-ants; Average num"ber of forms per plant late Dust ed Check June P4 3.83 3.96 July 19 14.01 12.75 August 24 42.55 (13.64 "bolls) 36.78 (11.53 bolls) At the final count, the dusted plots exceeded the check plots on the average "by 2.11 bolls per T)iant , although the long-staple cotton had not yet reached the peak of the fruiting stage. P.ecord of boll examinations for hem.ipterous insect damage; Percent of bolls punctured ^ate August 10 September 7 The amount of boll puncturing was reduced practically one-half through- out the main fruiting season in the dusted plots as compared with check plots. Dusted Check 8.75 19.50 14.00 26.75 - 15 - Yield of seed cotton in coraparalDle areas: The average yield per acre was 841 pounds in the dusted plots and 599 po\inds in the check plots. The average cain in the dusted plots over the checks v;as 242 pounds, or 40.4 percent. Rendition of lint (gin turn-out): On a field hasis the gin records show that the dusted plots yielded 0.7 percent more lint than did the check plots. Clas sing and grading records: Dusted Check No. of hales Percent Ho. of hales percent Total yield (first picking) 8 ~ 7 — arade No. 1 5 62.5 ~ !^To. 2 3 37.5 7 100.0 Staple 1-1/2" 2 25.0 4 57.1 i-e,'i6" 6 75.0 3 42.9 It is seen that a higher percentage of lint was produced and a bet- ter grade and staple was obtained in the dusted cotton. Value of Piaa seed Cotton: !vith a gin lint turn-out of 25 percent, 20 cents per pound for the lint and S14 per ton for the seed, 100 pounds of Pima seed cotton would give the following returns: 25 ^o-unds of lint at ?50.20 $5.00 75 pounds of seed at $0,012 .90 Total f^5.90 ?rom the extra yield attrihutahle to dusting, however, the follo^v^ ing costs T)er 100 pounds of seed cotton iirould have to he deducted: - 16 - Picking and hauiins $1.55 Ginning .60 Bagging and ties 0.06 Total $2.51 The net value of 100 pounds of Pima seed cotton vould therefore "be $5.90 minus $2.51, or t3.39 per hundred. Computing- the value of the gains and costs of dusting from the ahove figures, but without taking into consideration the increase in value of the dusted cotton due to an increased lint turn-out and a "better grade and staple, the value of 242 poujids of seed cotton gained per acre as a result of dusting is $8.20. The cost of seven apolications of dust at -.1.17 per ecre-application is '^8.19, v/hich shows a net gain of 1 cent per acre. How- ever, it will be noted that inf.ect populations in the dusted areas of this field were present in dar'-agin^; niribers for a period of 6 weeks, which should have required only 6 g-oplications of dust instead of 7 and would have left a profit of $1.18 per acre. The yields in this field vrere low, the imdusted check producing only 600 pounds of seed cotton per acre. Ordinarily Pima cotton produces from three-fourths to one bale per acre on siaitable land for Pima in Arizona, and a gain of 40 percent in cotton from such areas will justify several applications of dust and still give a profit. Definite information on the increased value of the lint resulting from the improvement in grade and staple in the airplane-dusted fields is not available at this time. A study of the classing and grading records shows, however, that this should be a considerable item. In fact, one large company that has been dusting with airolanes for several years con- siders tliat the increased value of the cotton alone will pay for all costs of dusting even though there is no increase in yield. Recommendations for Hemipterous Insect Control in Cotton Experiments conducted over a period of 7 years have shown that hemipterous insect damage to cotton can be profitably reduced by the use of several insecticides applied by hand and ground machinery. The in- creases in yields from 1 year's experiments with airplane dusting were not enough to pay the costs of dusting. This is attributed to the comparative- ly low insect pop\ilations in the experimental fields and the fact that more apolications of dust were made than v^ere needed. It is believed that further experiments will show that dusting with airplanes has certain advantages over ground machinery and can be profitably used for the control of hem- ipterous insects on cotton. A n\imber of factors influence the results that may be expected from dusting in various cotton-growing areas of the State, such as the soil fertility, surrounding crops, vd.ld host plants, size and stage of cotton growth, the relative proportion of the different species of injurious insects present, and the intensity of the insect populations. In planning control for hemipterous insects the general recommendations that k - 17 - follow are suggested. Eemipterous Insect Populations in Cotton Insect populations should be determined in all cotton fields be- fore dusting operations are begun. The methods used for making popula- tion counts are sweeping with a standard sweep net 15 to 16 inches in diameter, and plant examinations. In fields that are to be dusted, s^^reep- ings should be started the latter part of June or v/hen the cotton plants begin to set squares and bolls. The sweeping should be made at regular weekly intervals by maicing 300 or 400 net strokes in representative areas of the field. The sweeps should be made across the rows by hitting the tops of about every other plant with the net. VJhen 100 net strokes have been made, the insects and debris should be shaken down to the bottom of the net and sprinkled with while gasoline to kill or stupify the insects so they can be counted and recorded. I'Jhea. the sweepings have been com- pleted in a field, the total number of injurious hemipterous insects col- lected should be divided oy the number of lOO-stroke units, and if it is found that 12 to 15 specimens of injurious species are present per 100 net strokes, dusting should be started and continued at 7-day intervals until the numbers of injurious insects have been reduced below this point. Al- though very few leaf bugs or mirids may be present, it has been found that stinic bugs often migrate into cotton fields in great numbers, especially when stigar beets or alfalfa grown for seed is harvested. Since stinic bugs are heavy-bodied insects and feed principally upon the bolls located low on the plants, a smaller percentage of those present are collected by the sweeping method than of the lighter bodied mirids. In fields where heavy stink bug migrations occur, the plant examination method is used for de- termining the populations by examining 300 to 400 plants in representative areas of the field. '''Then 6 to 8 are found per 100 plants, poisoning should be started and continued as described above tmtil the stink bugs have been reduced below this point. Insecticides for Hemipterous Insect Control The insecticide to be used v/ill depend upon the insects present. If the insects are almost entirely mirids^ dygus spp. and Creontiades sp.), dusting sulfur may give the most economical control. If pentatcmids are present in any appreciable n-umbers, as they usually are in all cotton areas of Arizona, an arsenical- sulfur mixture will give better results. Repeated experiments have shoxm that sulfur alone does not give satisfactory control of stink bugs, while mixtures of paris green and sulfur and of cal- cium arsenate and sulfijT give economical control in fields vhere the popula- tions are great eno-ugh to justify the expense. The arsenical mixtures are also of value in controlling the cotton leaf perforator ( Bucculatrix thurb- eriella Busck) , the bollworm (Heliothis armigera (Hbn.)), and the cotton leaf worm ( Alabama argillacea (Hbn.)). The perforator and bollworm are nearly always present, and the leaf worm sometimes is present in Arizona cotton when dusting is needed for hemipterous insects and it sometimes causes considerable damage. Some of the gains that have been secured from dusting are probably partly due to the reduction in damage caused by these insects. - 18 - The proTDlem of the most econonical insecticide to use is further com- plicated ty Coats. At present prices dusting sulfur (98 percent 325-mesh, at least 95 percent pure) can he hou^t In quantities at around 4 cents a pound, the 20 percent C3.1ciijffl arsenate and 80 percent sulfur mixture at 5 to 5-1/2 cents, and the 7-l/2 percent paris green and 92-1/2 percent sulfur mixture at 5-l/2 to 6 cents a pound. The results of several years ofejppePiments show that for average conditions the calcium arsenate- sulfur mixture or the paris green-sulfur mixture will give the most profitahle re- sults, the choice depending largely on the preference of the individual grower and the availability of the materials. In both cases the materials should be thoroughly mixed by machinery for best results. These recom- mendations for insecticides are not to be considered as final, as they may be changed from time to time as investigations progress. Applications and Cost of Treatment V/hen insect populations reach coramercieilly damaging numbers the insecticide selected for use should be applied at the rate of 15 pounds per acre per application at 7-day intervals until the injurious species have been reduced below 12 to 15 insects per 100 sweeps, or, in the case of stink bugs, below 6 to 8 per 100 plants by the plant-examination method. In applying the insecticides \fith airplanes or any type of dusting machinery, a thorough coverage and uniform distribution of the dust are necessary. This can be best secured by dusting at night or early in the morning when atmospheric conditions are more favorable. 'Jhere large acreages are to be dusted, commercial airplane dusting companies will apply the insecticides for 40 to 50 cents per acre per application. I'/here poix^er dusters can be used advantageously, growers could probably apply their insecticides cheap- er than this. The expense of dusting will range from about $1.00 to $1,40 per acre per application. The number of insecticide applications required may vary from 2 to 9 per season, depending upon the ab\ir.dance of the in- sects, but usually 5 or 6 dustings are sufficient. Poisoning Bees Considerable apprehension has arisen over the danger of poison- ing bees by arsenical dusts used for the control of cotton insects, especially v/hen airplanes axe used for dusting. A few cases of damage to apiaries have been reported, but these have been due largely to the drift- ing of dust to adjacent fields around the edges of the cotton. The danger can be greatly reduced b;, cutting off the dust in time when nearing the end of the field and closing the hopper tightly while zooming and turning over adjacent property. The State entomologist at Phoenix should be notified several days in advance when dusting is to be done in a locality. He has arranged to notify all beekeepers in the vicinity so they can move their bees to other areas. Cooperation ^vith beekeepers by cotton growers and airplane pilots in taking precautions to prevent drifting of dust and giv- ing advance information as to when dusting w?.ll begin will reduce dazijger of damage to bees and the objections of beekeepers to dusting. - 19 - Summary The more important injurious hemipterous cotton insects in Arizona include three species of Pontatomidae , four species of Mlridae, and one species of Pyrrhocoridae. Several additional species inflict lesser in- juries. The damage consists of (l) injury to the small "buds, causing mal- formation in the grovrth of the plants; (2) injury to squares and small "bolls, causing them to shed; and (3) puncturing of the "bolls, resulting in shedding or in deformed and a"bnormal "bolls. The "boll injuries aro fol- lowed by lint staining, which lowers the quality and value of the crop; and the lint from punctured "bolls is more difficult to pick, causing dis- satisfaction among the cotton pickers. In addition to the damage to terminal "buds and squares, annual surveys of the cotton areas in the State have shown that on the average one "boll in every four is p-onctured "by hemipterous insects. The heaviest inju-ry invariably occurs in Yoma County, where an average of one-half of the cotton bolls are damaged, while the lightest damage occurs in Pima County, where only about 1 boll in 13 is damaged. In dusting for the control of hemipterous insects on cotton, the following general rules should be observed: (1) Commence dusting when 12 to 15 injurious hemipteroxis in- sects can be collected per 100 Bweei)-net strokes, or when 6 to 8 stink bugs are found by examining 100 plants. (2) Dust with calcium arsenate and sulfur (1-4), paris green and sulfur (1-12), or straight dusting sulfur. The pres- ent information indicates that dusting sulfur will give the most economical control of the mirids, but for gen- eral use where stink bugs and other insects are also pres- ent the arsenical- sulfur mixtures are better. (3) All insecticide applications should be made at the rate of 15 "Dounds per acre per application at night or early in the morning vfhen atmospheric conditions are most favor- able for dusting, (4) Insecticide applications should be made at 7-day intervals until insect populations have been reduced below damaging numbers. (5) The number of insecticide applications required may vary from 2 to 9, depending on the abundance of insects. (6) Under average conditions the cost of dusting will range from about $1.00 to $1.40 per acre per application. 1% '^''i^,''^-'^'^^"' Figure 1,— Power ground machine in operation, shoirtng satisfactory dust cloud. Figure 2. — Dusting airplane in operation. The dust cloud should settle among cotton plants in the same manner as shown in figure 1. iilii