INSECTS AND PLANT DISEASES 79 



both these kinds of insects. Some farmers plant a 

 "trap" crop that is, a crop earlier than the regular 

 one upon which the insects light to deposit their 

 eggs. As soon as the eggs are laid the crop is de- 

 stroyed, or else it is poisoned to destroy both the old 

 insects and the young ones when they hatch. 



Caution in Using Poisons. A word of caution in 

 the use of poisons is necessary here. Cases are on 

 record where people have been poisoned with paris 

 green intended for insects. Of course, it should never 

 be applied to cabbage or celery or any vegetable that is 

 used for food. Currants have sometimes been poisoned 

 in an effort to kill the currant worm. In no case 

 should deadly poison be used on fruit trees after the 

 fruit has begun to form. 



Other Plant Diseases. It is often convenient for the 

 farmer to fight other enemies of his crop, known as 

 plant diseases, while carrying on his fight against in- 

 sects, as one spraying may be made to do for both. 



Rust, blight, smut, rot and the like are diseases 

 which afflict the plant. They are caused by little, dust- 

 like particles, called spores, that float around in the 

 air and settle on healthy plants. Here they grow and 

 multiply very rapidly. They injure the plant by living 

 upon its sap in much the same way that lice and ticks 

 suck the l>lood of cattle and sheep. They must be 

 destroyed or they will destroy the plant on which they 

 feed. 



As soon as the spores make their appearance in the 

 field or orchard the farmer should begin his fight. If 



