SPRAYING 



87 



means of controlling insects and diseases on vegetables as well 

 as fruit crops; though vegetable growers have been somewhat 

 backward in recognizing this fact, and for the most part have 

 allowed the fruit growers to perfect spraying methods and appli- 

 ances. The principles of spraying for the control of insects and 

 fungous diseases are essentially the same whether the plant to 

 be protected is classified as a fruit or a vegetable. 



For effective spraying the first essential is a knowledge of the 

 nature of the organism to be controlled. There are three classes 

 of enemies that can be controlled by spraying. They are chewing 



Fig. 4: 



-Potato beetle, a chewing insect: a, eggs; 

 e, wing cover of adult. 



h, larvae; c, pupa; d, adults; 



insects, sucking insects and fungous diseases. These three classes 

 of enemies are so different that different spraying materials are 

 needed to control them. 



The chewing insects bite off portions of the plant, chew them 

 up and swallow them, the same as any of the higher animals 

 take their food. Potato beetles, cabbage worms and the various 

 forms of caterpillars belong to this class (Fig. 47). The simplest 

 means of killing such insects is to poison their food. This is 

 accomplished by appl3ring a thin, uniform coating of poison over 

 all parts of the plants to be protected. The poison must be suffi- 

 ciently virulent to cause death of the insects when eaten in rela- 

 tively small quantities, so that no large part of the plant need be 



