66 



CIRCULAR 270, U.S. DEPARTMENT OF AGRICULTURE 



SPRAY MATERIALS 



Fortunately, most of the insect pests of fruit trees spend at least 

 part of their lives in situations that enable the fruit grower to control 

 them by means of sprays. Annual crops may often be protected from 

 serious insect injury by following certain practices of planting, 

 harvesting, cultivating, and crop rotation, but with fruit trees these 



methods are usually out of the question. 

 Spraying is expensive, but its cost consti- 

 tutes only a small proportion of the value 

 of the crop. 



Insects feed in two distinct ways. Some 

 bite off and swallow portions of the fruit 

 or foliage. Many of these biting insects 

 may be destroyed by keeping the trees 

 covered with a poisonous material which the 

 insects eat with their food. The young of 

 the codling moth and other moths, beetles, 

 sawflies, grasshoppers, and crickets are 

 examples of biting insects. Other insects 

 have mouths in the form of a sucking ap- 

 paratus which they insert into the plant 

 tissue and through which they draw out 

 the plant juices. These insects are not 

 affected by stomach poisons placed on the 

 surface of the leaves or fruit, and it is not 

 possible to poison the plant juices without 

 injuring or killing the plants; therefore 

 materials known as contact insecticides are 

 used for their control. These materials 

 poison the insects through their breathing pores, or by a corrosive 

 action on their bodies. The scale insects, aphids, leaf hoppers, tree 



Figure 79.— Young of a laeewing fly 

 Six times natural size. 



Figure 80.— Eggs of a lacewing fly 



hoppers, and the true bugs are examples of sucking insects. Red 



spiders also feed in this manner, although they are not true insects. 



Several spray materials have been employed so extensively and 



successfullv that thev have "become standard insecticides. The worth 



