July 1946 k-697
United states department of Agriculture
AgrEi. f research Administration
Bureau of intomology and rlant Quarantine
EXPaiIMhV TS WJITH DDT AND OTHhA NS4 DUSTS FOR CONTROL OF LYGUS SPP.
AND THE ALFALFA aiAWiL ON 6aD ALFALFA
y Y. V. Lieberman and 1. A. Hare,
division of #ereal anri rorage insect investigations
A preliminary test of DDT, sabadilla, and pyrethrum dusts for control of Uyg spp. on seed alfalfa was me4e in 1944 on small field plots at uandy, Millard county, Utah.:/ Ltay vDT showed definite promise of giving satisfactory control of these bugs.
Testing of insecticides was continued in 1945 at alta and
Gandy, Utah, with the emphasis on DT. Large field p>7ots, averaging 4.8 acres, were used to provide reasonably normal visitation by pollinating bees and to minimize effect of drift of WT dusts. mach plot was dusted only once, during the prebloom early bud to late bud) stage, ubservations have showm that danger of poisoning pollinating bees is thus avoiee, cause 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. rhe tractor 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. A 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. buch counts were taken just before dusting, 3 days after dusting, and thereafter at weekly intervals for 6 weeks. Control estimates are based on the average of those sweepings made in each plot during the 6 weeks following dusting.
I/Lieberman, F. V. Experiments with ijDT, sabadilla, and pyrethrum dusts for control of igus spp. on seed alfalfa. U. S. bur. of mit. and Plant wuar. b-658, 7 pp. (Processed.) 1945.
Results with WAT are shown by the data from second-crop experiments in the uelta tract, which are summarized in table 1. 'Ahe dosages used were 0.6, 1, and 2 pounds of uir per acre, applied July 13 to 15 as 20 pounds of mixed dust containing 3, 5, and 10 percent of LflWT in pyrophyllite.
Table l.-mffectiveness or uvT in controlling g spp. on secondcrop alfalfa grown for seed, uelta, utah, July-August 190>.
Treatment Average Average yilncrease in
(Pounds per acre) Lygu bugs reduction Oeed yield seed yield
Number Percent Pounds per acre Pounds
,eries 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)
I)T 2.0 48 80 209 93
heck 235 -- 116
Control of b 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. Nymphs 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 treatments could not then have been prebloom. because of the tardy hatching of 1,gs nymphs on second growth, all untreated plots bloomed as fully as those dusted. damage to buds was almost negligible, however, moderate to almost complete stripping of blossoms had occurred in most check plots by August 6, 3 weeks after dusts were applied. rhe 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 considerably in size. Ln the field having the highest population a peak of 1,274 L bugs per 100 net strokes was reached on August 6. Notwithstanding, the 2-pound dosage of LDT gave a reduction of 91 percent,
the best achieved in Delta tract experiments. u control and crop
return increased consistently with the dosage of ADT applied. The application of 2 pounds per acre appeared to be fully justified as judged by both control and crop return.
n two experiments performed at uandy, Utah, the same three dosages of DT duct were tested on second-crop seed growth. Control of g 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 hydrated lime and ueorgia talc, and the other containing 0.1 percent of pyrethrins and 0.625 percent of piperonyl cyclohexanone in talc. Although the immediate kill of jgu by both these dusts was excellent, neither had noticeable residual effect and the single applications failed to control the bugs. Nymphs of us 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 with 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. results are summarized in table 2.
Table 2.-Effectiveness of DDT, sabadilla, and pyrethrum-piperonyl
cyclohexanone dusts in controlling Lygus app. on second-crop
alfalfa grown for seed, Gandy, Utah, July-eptember 1945.
Experiment 1 xperiment 2
Treatment us Reduction gu Reduction
(Pounds per acre) population population
Number Percent Number Percent
LuT 0.6 25 86 96 73
1.0 44 75 29 92
2.0 23 87 5 99
Sabadilla 233 0 427 0
cyclohexanone 247 0
Check 173 352 -
UNIVERSITY OF FLORIDA
,;. .- I I I I I II IIJI Ill 11l1l l
3 1262 09238 7512
experiments at Gandy and Delta indicated that uU' dusts would provide satisfactory control of both a and the alfalfa weevil,
te postica ibn.) on first-crop seed growth. rive dosages of
uDT 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 a senate at the recommended dosage of 2 pounds per acre. controll of & by the same dosages of ADT 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, toe, that two prebloom applications on these slower growing ard slower maturing fields might be necessary to give best results for control of these two pests together.
In both the Delta and iandy experiments leafhoppers, aphids, and
thrips common to alfalfa fields in millard county were effectively controlled by the application of 2 pounds of u)T per acre. The results of these experiments indicate that when applied as a dilute dust this is the most satisfactory dosage yet tested against g and other alfalfa seed pests of central utah, from the point of view of control of insects and increase in yield. -'his dosage can be satisfactorily applied as a single treatment with a dust containing 10 percent of ODT in pyrophyllite or similar carrier, at the rate of 2D pounds per acre.
in order to avoid the possibility of poisoning bees, DT 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 byg bug does not usually injure seed alfalfa materially until the plants produce buds. hereafter 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 g nymphs from eggs laid in the seed growth. If
L 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 kiaown about the quantities of TD remaining on the plants at harvesttime, and the toxicity of dusted plants to livestock, vDT 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.