STUDIES OF THE PINK BOLLWORM IN MEXICO 
59 
made to do the work on a commercially profitable basis. On the 
contrary, the plan followed was to keep the plants thoroughly covered 
with poison during the entire period of treatment. Some of the 
plats were dusted with hand guns and others with 2-row mule dusting 
machines. 
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Fig. 15. — Progress of the infestation of green bolls in poisoned and check plats as shown by weekly 
examinations, 1921 poison tests 
The air in the Laguna district is very dry and there is considerable 
wind. It was therefore found that applications must be made every 
five days in order to keep the plants fairly well covered with poison. 
Applications were repeated after rains. A period of calm lasting 
an hour, more or less, usually occurs at 5 or 6 o'clock in the morning, 
and the applications were made at that time. Dew was usually 
absent or so light as to be hardly noticeable. The conditions for 
dusting were therefore far from ideal. 
The 1921 plats may be divided into three groups. Poisoning on 
those of the first group (plats 2, 6, 10, and 14) began about the middle 
