420 CONTROLLING INSECTS AND PLANT DISEASES 

 INSECTICIDES AND FUNGICIDES 



The principles involved in combating insects are based upon 

 their methods of feeding. Chewing or biting insects are killed 

 by arsenical poisons. Insects with sucking mouth parts live upon 

 the juices of plants and cannot be killed by such poisons. If they 

 are to be killed by spraying, it must be with a l 'contact insecticide, " 

 i.e., some material such as oil or dust which will smother the 

 insect by clogging the breathing pores located along the sides of 

 the body. 



FIG. 293.*-A spray pump operated by hand which pumps the liquid from the big tank and 

 delivers it at high pressure through the spray hose. (New Jersey Station.) 



Fungous diseases can be usually prevented by the application 

 of a fungicide applied by spraying the surface of the plant before 

 the disease finds a starting place there. 



In many cases, spraying may be made to serve two purposes. 

 Thus by combining two spray materials such as a fungicide with 

 an arsenical poison we may combat a fungous disease and kill 

 leaf-eating insects. Examples of these combinations are given in 

 this chapter. 



Arsenical Poisons. White arsenic is a cheap form often used 

 in preference to Paris green or arsenate of lead. Arsenic alone is 

 injurious to the leaves and should be combined with sal soda at 

 the rate of one pound of arsenic to two pounds of sal soda dis- 



