30 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE. 
elevations flown, air conditions, regularity of hopper operation, and 
other considerations. Some flights were made at a reduced feed, 
using deliberately narrow strips, while others were made at a higher 
feed, widening these strips as much as possible. 
As a result of these studies and the observations on the leaf worm 
control effected, it was found that by properly controlling the dust 
delivery it was possible to give effective treatment to strips varying 
from 25 to approximately 500 feet in width. Of course in the 
smaller fields, especially in those immediately adjoining obstructions, 
where definite direction of the dust was particularly desirable, the 
narrow strips were utilized, while in the larger fields, where it was 
desirable to take as much area at a time as possible, the feed was in- 
creased to take care of wide strips. These wide strips are possible 
only under favorable air conditions, and are especially suitable when 
the plants are moist. As the breeze increases later in the day and the 
plants become dry, the poisoning can be better controlled and the 
applications made more thorough and accurate by taking narrower 
strips at a reduced rate of dust delivery. 
In all this field work it was almost the universal rule that ex- 
cessive applications were made, as compared with the treatments 
desired in each instance, because in operating over practically every 
field it was necessary to repeat some flights to correct faulty dust 
delivery through the feeder. For instance, the feeder might choke 
for only a second or two about the middle of a field, and with the 
crude system of signaling available, it would often be necessary 
to have the pilot make one or more trips completely across this 
field to make sure of treating the area which had been skipped. In 
addition, owing to flimsy construction, it was impossible to shut 
off the feeder completely, and consequently there Mas great waste 
of material in banking through the turns outside the field. 
For these reasons the figures which were obtained on poundage 
delivery should not be taken too seriously, though they are in a way 
rather striking. In using the standard calcium arsenate for leaf- 
worm control, following various methods, the poundage delivered to 
the different fields varied from slightly less than 2 pounds Der 
acre to about 11 pounds per acre. After fairly standardized methods 
had been worked out, however, and had been checked by the amount 
required for leaf worm control, it was found that from 2 to 4 pounds 
of calcium arsenate per acre was sufficient for the maximum effect. 
The results of these dosages so far as leafworm control was con- 
cerned, were quite equal to those obtained from the use of ordinary 
dusting machines applying the poison at the rate of 6 or 7 pounds 
per acre. 
In every instance the effect of the application on the worm was 
very careiully watched, with respect to the mortality not only of 
the worms in the field at the time, but also of those which hatched 
later from the eggs then present. As with any form of dusting 
apparatus, it was difficult to control infestation when the plants had 
been rather thoroughly skeletonized before treatment and provided 
very little leaf surface on which the poison could adhere. On the 
other hand, the control which resulted from airplane dusting on 
such fields was fully equal to that which followed the use of the 
most efficient hand guns or wheel traction machines, ordinarily used 
for boll-weevil dustinff. Under conditions more favorable for con- 
