70 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 1940 
slowly nnrl the peak occurred Inter than in the warmer or lower 
levels. This explains Why the weevils appear in the fields later in 
the season in the higher areas. 
Large-scale field tests involving the dusting of the more heavily 
infested edges of the field of Austrian winter field peas were con- 
tinued in 1939. The results as a whole were satisfactory, and the 
dusting of Austrian winter peas is now generally practiced through- 
out the area planted to this important seed crop. Results in general 
indicate that the germination of these peas is governed almost solely 
by the presence of the weevil grubs; and that if the weevil infesta- 
tions can he held at less than 10 percent, germination tests satisfactory 
to the industry can be maintained. This has been accomplished for 
the peas in two successive seasons in the areas under observation; 
and while substantial improvements may be made in the present 
method of reducing pea weevil infestations in Austrian field peas, 
the present methods may be considered reasonably satisfactory. 
Even with applications of dusts, however, the importance of early 
harvest and prompt fumigation of the peas after harvest should not 
be overlooked, as a delay of 5 to 10 days from the earliest possible 
harvest date may increase the loss manyfold. 
CABBAGE CATERPILLARS 
A control experiment against cabbage caterpillars was carried 
out on the scale of a commercial planting, of fall-grown cabbage 
at Charleston, S. C. Its purpose was to test the practical applica- 
tion of the results obtained in toxicity and control experiments, con- 
ducted during previous years, which had for their major objective 
the determination of a satisfactory control program for caterpillars 
on cabbage with special reference to the avoidance of a poisonous 
insecticidal residue on the marketed product. The program in this 
field experiment consisted essentially of applying cryolite-containing 
dust mixtures at regular intervals before the cabbage began to form 
heads, and of rotenone-containing dusts during the heading stage 
of plant growth. Cryolite was used because it is toxic to the corn 
earworm and cutworms as well as to the cabbage looper, the diamond- 
back moth larva, and the imported cabbageworm, whereas rotenone- 
containing dusts are effective only against the three last-named pests. 
Cryolite is not recommended for use after the cabbage plants have 
begun to head because of the danger that poisonous deposits may 
be left on them at harvest time. 
A total of 10 applications of insecticidal dusts, made with equip- 
ment ordinarily used by the grower, were given at approximate inter- 
vals of 10 days between August 21 and November 15. This included 
the period of plant growth from soon after the plants appeared above 
ground in the field until the weather was sufficiently cool to prevent 
further insect development and damage. The first seven applications, 
made before the cabbage began to form heads, consisted of a dust 
mixture of synthetic cryolite and talc, 1 part to 2 parts, respectively, 
by weight, put on at a rate of 21 pounds per acre per application. 
The la^t three applications, made during the heading stage of plant 
growth, consisted of b derris-talc dust mixture containing l percent 
of rotenone. put on at a rate of 22 pounds per acre per application. 
Denis root powder was added to the cryolite-dust mixture for the 
