1G ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 194 1 
pounds of seed cotton per acre, or 48 pounds per application, and the 
latter a gain of 210 pounds per acre, or 70 pounds per application. 
However, on the lighter soils where cotton does not fruit so late in 
the season, control of the early weevil damage is more important. 
Each year tests are conducted with various materials in the hope of 
finding an insecticide better than calcium arsenate for boll weevil con- 
trol. Sodium fluosilicate, one of the most promising insecticides 
tested, prevented the proper development of the fiber and resulted in 
significant reduction in yield in one variety of cotton, though not in 
ot hers. Barium fluosilicate, cryolite, DDT, and other materials tested 
were all inferior to calcium arsenate. 
In tests to obtain additional information on mopping entire fields 
with molasses-calcium arsenate, 55 fields containing 27G acres were 
mopped at 6 localities in South Carolina, Georgia, Mississippi, Louis- 
iana, and Texas. Half of the mopped area in 19 fields at 4 localities 
was also dusted with calcium arsenate when needed. The average gain 
for all 55 mopped fields was 83 pounds of seed cotton per acre ; for the 
19 most heavily infested fields, 142 pounds from mopping and 290 
pounds from mopping and dusting. The gains from mopping were 
not significant at any locality, while dusting gave significant gains at 
3 localities. 
CHEMICAL DEFOLIATION FOR CONTROLLING COTTON INSECTS 
Tests of chemical defoliation of cotton indicated that this treatment 
controls insects, improves the grade of fiber, increases the efficiency of 
mechanical cotton harvesting, and reduces the labor required for hand 
picking.. In experiments in Mississippi, Texas, and Arizona dusting 
with 10 to 20 pounds per acre of calcium cyanamide, a commercial 
nitrogenous fertilizer, caused complete defoliation within a few days 
when moisture was abundant and the plants were succulent, but poor 
defoliation of water-stressed plants. Defoliation causes the small 
bolls and squares to shed and the mature bolls to open promptly and 
uniformly without a reduction in staple strength. This checks boll 
weevil breeding, prevents staining of lint by aphids or leaf worms, 
ermits all the crop to be picked at one time by hand or mechanical 
arvesters, reduces the trash, and improves the grade of lint. 
COTTON APHIDS 
The addition of nicotine to calcium arsenate to prevent the build-up 
of aphids increased the yields of seed cotton in 1943 by 137 to 435 
pounds per acre in Mississippi, by 120 to 446 pounds in Louisiana, and 
by to 132 pounds in Texas. The average gain in yield of seed cotton 
in 78 experiments at Tallulah, La., during 1939-43 was 128 pounds per 
acre when calcium arsenate dust was used against boll winwils and 393 
pounds when ealeium arsenate plus nicotine was used against both boll 
weevils and aphids. In other words, there was an increase in yield of 
2G5 pounds when nicotine was added. In general, nicotine sulfate, 
free nicotine, and several fixed nicotines were about equally effective 
per pound of actual nicotine. Sat is factory aphid cont rol was obtained 
in commercial dusting with airplanes or ground machinery at any 
time of day or night when atmospheric conditions were favorable for 
the dust to settle. None of the synthetic materials tested, including 
