BOLL WEEVIL CONTROL BY USE OF POISON. 9 
CONDITIONS UNDER WHICH TO MAKE APPLICATIONS. 
The time of day for making these applications is quite an im- 
portant point. Thoroughly successful results can be secured only 
when every part of the cotton plant is absolutely covered by the fine 
particles of poison dust. It has been found that when the humidity 
is low and there is any breeze whatever, the dust cloud will drift 
away above the cotton plants and will not filter down and cover all 
portions of the plant surface. The best time to dust is when the 
humidity is high, the air calm, and the plants moist with dew, so that 
the dust will adhere readily. This condition is experienced generally 
only at night and thus it has been necessary to do nearly all of the 
dusting work during the night, early in the morning, or late in the 
evening. De 
Tt has been found that while the weevils can be controlled by ap- 
plications made under unfavorable conditions, the results are gen- 
erally very erratic and unsatisfactory, and at best can only be ex- 
pected to hold the weevils in check without accomplishing any con- 
siderable diminution in their numbers. This, of course, means that 
the application must be repeated at very short intervals and makes 
the entire operation very risky. Therefore the best economy un- 
doubtedly is to reduce the acreage allotment of the different machines 
to the point where it is not necessary to operate when the plants are 
dry or while a breeze is blowing. This will increase the outlay for 
machinery, but it makes the entire operation much safer. Operation 
under unfavorable conditions should be attempted only in case of 
absolute emergency and fields which have been treated under such 
conditions should be watched carefully to determine whether the 
requisite degree of control has been secured. 
ARRANGEMENT OF POISONING SCHEDULE. 
Those features of poisoning which include the number of applica- 
tions, the time of starting, time of ending, and time interval between 
applications are of course exceedingly variable and depend upon 
purely localized conditions. But a number of fundamental factors 
govern these points which should be understood in order properly to 
plan the operation. In the first place, as has been mentioned, a cer- 
tain degree of weevil abundance may be permitted without resulting 
- In any reduction in the cotton crop. Furthermore, it is necessary to 
control the weevils and hold them below the point of injury for only 
a limited time until the plants have had an opportunity to set their 
maximum crop. Another important point which must be considered in 
this connection is the fact that poison reaches and kills only the adult 
weevils present in the field and has no effect whatever on the imma- 
174542°—Bull. 875—20 
2 
