CONTROL OF CITRUS THRIPS IN CALIFORNIA AND ARIZONA. bb 
In the above calculation the cost of spraying an acre of 18-year-old 
trees is higher than will usually be the case, since, as a rule, the 
grower is obliged to have a team on hand all the time and may there- 
fore reduce the item of team hire; he may also be able to reduce the 
cost of labor somewhat in many cases. In seasons of gross infesta- 
tion, and in certain orchards every season, the returns will be greatly 
increased over the figures given because of the excessive infestation in 
such seasons and orchards. 
WASHINGTON ; GOVERNMENT PRINTING OFFICE ; 1915 
