DUSTING COTTON FROM AIRPLANES. 31 
trol. where the worm infestation had not progressed quite so far. 
the results were of course much more satisfactory. 
It was quite noticeable, however, that the distribution of the 
material in the path of the plane was not absolutely uniform 
throughout the width of the strip. In several instances a single 
application was made in a fairly heavily infested field containing 
many eggs which hatched later and were then allowed to develop 
without further treatment. Perfect control was always obtained in 
a strip from '2~> to 5G feet wide directly under the plane, but beyond 
this strip the dosage of poison was somewhat lighter and more of 
the worms hatching from the eggs managed to survive, so that the 
fields treated in this manner with very wide swaths presented 
alternating strips thoroughly and partially controlled. On the 
other hand, sufficient control was exerted to prevent really serious 
commercial damage to any of the cotton, and where two applica- 
tions were made in such fields, practically complete control was 
secured. 
This experience was compared with the work which was being- 
done at the same time on other properties in controlling the leaf- 
worm with calcium arsenate with different types of ground machines, 
and it was found that to control this unusually heavy infestation 
two applications of calcium arsenate were usually necessary. As 
nearly as could be determined, about '2 pounds of calcium arsenate 
per acre delivered from the airplane proved as effective as 5 pounds 
per acre delivered from a ground machine. Of course the effective- 
ness of this application was measured only by leafworm control, 
and is by no means settled as regards the boll weevil. 
TESTS OF VARIOUS INSECTICIDES. 
DIFFERENT CALCIUM ARSENATES. 
To contrast with the results secured from calcium arsenate of the 
usual type a number of other varieties were utilized. By a slight 
variation in manufacturing methods, calcium arsenate can be pro- 
duced with practically the same chemical analysis, but with a great 
range in the physical characteristics. For example, its volume may 
range from ¥) to 250 cubic inches to the pound, and the material 
ordinarily found on the market varies from 60 to 150 cubic inches to 
the pound. This difference is largely due to difference in the size 
of particles. 
To determine the behavior of these different dusts in the air. flights 
were made with a product testing about 60 and another about 135 
cubic inches to the pound. The heavier material ( 60 cubic inches) 
did not behave very well in the air and dropped nearly directly to 
the ground from the plane, not being as subject to the influence of 
the slip stream as the standard material | '.mi cubic inches). The light 
material behaved very differently. It had been feared that it was 
exceedingly light that when released in the air it would float away 
and never reach the plants, but it proved to be subject to the Influence 
of the slip stream and made a beautifully controlled cloud. Unfor- 
tunately it was not possible to make determinations of adhesion of 
this material, but as far as visual observation was possible it seemed 
to work fullv as well as the standard material. 
