July 1%6 £-697 
 
 United states Department of Agriculture 
 Agricultural ite search Administration 
 Bureau of jyitomology and riant Quarantine 
 
 EXPiSKIMi^Ta WITH DDT AND OTHLK Ntfrf DUSTS FOR CONTROL OF LYGUS SPP. 
 AND THE ALFALFA ,<EEVlL ON SEED ALFALFA 
 
 uy F. V". Lieberman and A* Hare, 
 division of oereal and rorage insect investigations 
 
 a preliminary test of DDT, sabadilla, and pyrethrum dusts for 
 control of lffgu s spp. on seed alfalfa was made in 1944 on small 
 field plots at uandy, Millard uounty, Utah.V Only uDT showed 
 definite promise of giving satisfactory control of these bugs. 
 
 Testing of insecticides was continued in 1945 at Delta and 
 Gandy, Utah, with the emphasis on DDT. large field plots, averag- 
 ing 4*8 acres, were used to provide reasonably normal visitation by 
 pollinating bees and to minimize effect of drift of DDT dusts, j*ach 
 plot was dusted only once, during the prebloom (early bud to late bud; 
 stage, observations have shown that danger of poisoning pollinating 
 bees is thus avoided, because they do not begin to visit the fields 
 until the flowers open. All dusts were applied with a crop duster 
 mounted on a tractor and operated from its power take-off. The trac- 
 tor was operated at a speed of 3.75 miles per hour and the duster fan 
 at slightly more than 4000 revolutions per minute. The dusts were 
 discharged several inches above the tops of the alfalfa plants through 
 a boom fitted with 12 v-type nozzles spaced approximately 16 inches 
 apart and connected individually to the fan chamber by flexible tubing, 
 it 15-foot canvas apron was attached to the boom. 
 
 Dusting and all subsequent operations in handling, harvesting, 
 and threshing the crop closely approached actual farm practice, 
 insect counts taken in the plots were based on 100 strokes of a 15-inch 
 insect net. such counts were taken just before dusting, 3 days after 
 dusting, and thereafter at weekly intervals for 6 weeks. Control esti- 
 mates are based on the average of those sweepings made in each plot 
 during the 6 weeks following dusting. 
 
 =f .Lieberman, F. V. Experiments with uDT, sabadilla, and pyre- 
 thrum dusts for control of lygua spp. on seed alfalfa. U.S. but. 
 of mt. and plant v*uar. ur-658, 7 pp. [Processed.} 1945* 
 
Results with DDT are shown by the data from second-crop experi- 
 ments in the Delta tract, which are summarized in table 1. The dosages 
 used were 0.6, 1, and 2 pounds or DDT per acre, applied duly 13 to 15 
 as 20 pounds of mixed dust containing 3, 5, and 10 percent of DDT in 
 pyrophyllite. 
 
 Table 1. — effectiveness or uDT in controlling iffgus spp. on second- 
 crop alfalfa grown for seed, u»elta, Utah, July-August 1941? • 
 
 Treatment Average Average Increase in 
 
 ^ Pounds per acre; iygus bugs reduction oeed y ie l d se ed yield 
 
 Numbe r percent Pounds per acre Pounds 
 
 series 1 (3 replications; 
 
 DDT 
 
 0.6 
 
 129 
 
 51 207 
 
 28 
 
 
 1.0 
 
 105 
 
 60 237 
 
 58 
 
 
 2.0 
 
 77 
 
 71 314 
 
 135 
 
 Check 
 
 
 264 
 
 179 
 
 
 
 
 series 
 
 il (5 replications; 
 
 
 DDT 
 
 2.0 
 
 48 
 
 80 209 
 
 93 
 
 Check 
 
 
 235 
 
 116 
 
 
 Control of lygus was spectacular for 3 to 4 weeks. Thereafter 
 noticeable numbers of nymphs hatching in the plots escaped the effect of 
 the DDT, but the increase in number of bugs on the plants was not 
 enough to warrant a second treatment, wymphs on second-crop growth 
 were tardy in hatching with respect to crop development, and most plots 
 were dusted before many nymphs had appeared on the plants. More complete 
 control might have been obtained if the dusts could have been applied 
 nearer to large-scale hatching (1 week to 10 days later;, but the treat- 
 ments could not then have been prebloom. because of the tardy hatching 
 of lygus nymphs on second growth, all untreated plots bloomed as fully 
 as those dusted, uamage to buds was almost negligible. However, moder- 
 ate to almost complete stripping of blossom? had occurred in most check 
 plots by August 6, 3 weeks after dusts were applied. The protection 
 afforded by the dusts provided a striking contrast between the treated 
 and untreated areas in the more heavily populated fields at that time. 
 
 populations in the different plots were moderate but varied con- 
 siderably in size, in the field having the highest population a peak 
 of 1,274 lygus bugs per 100 net strokes was reached on August 6. Not- 
 withstanding, the 2-pound dosage of DDT gave a reduction of 91 percent, 
 
- 3 - 
 
 the best achieved in Delta tract experiments, iygus control and crop 
 return increased consistently with the dosage of DOT applied. The 
 application of 2 pounds per acre appeared to be fully justified as 
 judged by both control and crop return. 
 
 in two experiments performed at uandy, Utah, the same three dos- 
 ages of DDT dust were tested on second-crop seed growth. Control of 
 Iggna bugs was considerably better than at Delta, largely because the 
 applications were made just as large-scale hatching of the nymphs 
 began, unfortunately, yields were spoiled by windstorm and frost, 
 included in these experiments were two other new dusts, one containing 
 20 percent of ground sabadilla seed in a 1:3 mixture of hydra ted lime 
 and ueorgia talc, and the other containing 0.1 percent of pyre thr ins 
 and 0.625 percent of piperonyl cyclohexanone in talc. Although the 
 immediate kill of iygua by both these dusts was excellent, neither had 
 noticeable residual effect and the single applications failed to control 
 the bugs. Nymphs of lygus quickly became more numerous than they were 
 in these plots before the dusts were applied, and the plots were heavily 
 damaged, one of those treated wit^i the sabadilla dust failing to bloom. 
 The sabadilla dust was applied at the rate of 35 to 40 pounds per acre 
 and the pyrethrum-piperonyl cyclohexanone dust at 25 pounds per acre, 
 ae suits are summarized in table 2* 
 
 Table 2. — Effectiveness of DDT, sabadilla, and pyrethrum-piperonyl 
 cyclohexanone dusts in controlling Lygus spp. on second-crop 
 alfalfa grown for seed, Gandy, Utah, July -September 1945* 
 
 ■fatxperiment 1 isxperiment 2 
 
 Average Average 
 
 Treatment Juygus Reduction iygus Reduction 
 
 (Pounds per acre; population population 
 
 
 Number 
 
 Percent 
 
 Number 
 
 Percent 
 
 DDT 0.6 
 
 25 
 
 86 
 
 96 
 
 73 
 
 1.0 
 
 44 
 
 75 
 
 29 
 
 92 
 
 2.0 
 
 23 
 
 87 
 
 5 
 
 99 
 
 oabadilla 
 
 233 
 
 
 
 427 
 
 
 
 ryrethrum-piperonyl 
 
 
 
 
 
 cyclohexanone 
 
 247 
 
 
 
 
 
 Check 
 
 173 
 
 
 352 
 
 
UNIVERSITY OF FLORIDA 
 
 , ^ r 1 1 1 ' 
 
 - 4 - 3 1262 09238 7512 
 
 JSxperiments at Gandy and Delta indicated that uui dusts would 
 provide satisfactory control of both iygua and the alfalfa weevil, 
 I tiypera postica hbn*; on first-crop seed growth, rive dosages of 
 wDT ranging from 1 to 2*4 pounds of active ingredient per acre gave 
 substantially better control of the alfalfa weevil than is obtained 
 by the use of calcium arsenate at the recommended dosage of 2 pounds 
 per acre, control of ijgus by the same dosages of DDT dust appeared 
 equally as good as that obtained on second-crop seed growth, but 
 mortality of nymphs inflicted by storms 3 to 6 days after applications 
 of dusts somewhat obscured actual results. There was indication, too, 
 that two prebloom applications on these slower growing and slower 
 maturing fields might be necessary to give best results for control of 
 these two pests together* 
 
 In both the Delta and liandy experiments leafhoppers, aphids, and 
 thrips common to alfalfa fields in Millard county were effectively con- 
 trolled by the application of 2 pounds of ulf£ per acre. The results of 
 these experiments indicate that when applied as a dilute dust this is 
 the most satisfactory dosage yet tested against lygus and other alfalfa 
 seed pests of central Utah, from the point of view of control of insects 
 and increase in yield. This dosage can be satisfactorily applied as a 
 single treatment with a dust containing 10 percent of DDT in pyrophyllite 
 •r similar carrier, at the rate of 20 pounds per acre. 
 
 In order to avoid the possibility of poisoning bees, DDT should not 
 be applied to the crop after it blooms. Honeybees and wild bees which 
 visit the alfalfa blossoms are essential to the production of seed 
 because of their pollinating activity, ihe urgus bug does not usually 
 injure seed alfalfa materially until the plants produce buds. There- 
 after buds, flowers, and seed pods are subject to heavy attack, oeed 
 alfalfa should therefore be dusted during the bud stage just as soon as 
 damage to buds is evident* This time usually marks the beginning of 
 volume hatching of iygus nymphs from eggs laid in the seed growth, if 
 Lygus nymphs are not numerous while the plants are budding, dusting may 
 be delayed until the plants are just beginning to bloom, but no longer* 
 
 Until more is known about the quantities of DDT remaining on the 
 plants at harvesttime, and the toxicity of dusted plants to livestock, 
 uDT should not be used on alfalfa crops that are to be pastured or cut 
 for hay, meal, or silage, when used on an alfalfa seed crop, the chaff 
 and straw from threshing should not be fed to livestock, at least not 
 until more information is available on the residues of DDT present in 
 the threshings, and the possible direct or indirect toxic effects of 
 these residues on livestock and man*