BOLL WEEVIL CONTROL BY USE OF POISON. 15 
formed. This usually means that the plant has reached the limit 
of its ability to mature fruit. Naturally there is no advantage in 
attempting to protect these forms, and poisoning during this period, 
if conducted after the retained bolls are sufliciently large to escape 
weevil injury, is bound to be profitless. The time when this con- 
dition is reached varies widely with the season as well as with the 
soil fertility, and these factors must always be taken into considera- 
tion in deciding whether additional poisoning is justified. 
EFFECT OF RAIN ON AN APPLICATION OF POISON. 
The effect of rain upon the application of calcium arsenate is a 
subject of much importance. Experience has shown that a certain 
amount of rainfall is desirable during the poisoning operations as 
it induces the formation of dew, makes conditions more nearly ideal 
for dusting, and apparently increases the amount of mortality se- 
cured from the applications. Poisoning operations have been con- 
ducted during periods of extreme drought when there was almost 
no dew formation, but under such conditions it has been very difficult 
to secure a thorough degree of control. On the other hand, ex- 
cessive rain is detrimental, owing to the difficulty of getting the 
poison to stay on the plants long enough to control the weevils. 
This was especially true during some of the work in the extreme 
southern districts in 1919. The rains encountered in this work 
were excessive and in many cases occurred almost daily. Under 
such conditions weevil poisoning can easily become an absolute im- 
possibility but, as far as that is concerned, such conditions make 1% 
practically impossible to raise cotton at all. 
It has been found that when an application is made under unfavor- 
able conditions and the plants are dry, even a sight shower occurring 
a short time later will wash off practically all the dust, while if con- 
ditions during the application are more favorable for a large quan- 
tity of the poison to adhere to the plants, a much heavier rain will 
not interfere seriously with the effect of the treatment. As a gen- 
eral rule it seems advisable to repeat an application immediately if 
a drenching rain falls within 24 hours after treatment. Until more 
information is secured on the subject, it undoubtedly will be best to 
follow some such rule as this, but the question of degree of weevil 
infestation and the conditions under which the application has been 
made should undoubtedly be considered in connection with the ques- 
tion of whether the application should be repeated. 
STARTING POISONING IN THE PRESENCE OF A COMPLETE INFESTATION. 
Many farmers make no move toward weevil poisoning until the 
crop is seriously infested and in fact almost totally destroyed by the 
