INSECTS AND DISEASES 55 



mon. Arsenate of lead is usually used at the rate 

 of from two to five pounds to 50 gallons of water, 

 sprayed upon the plants when the insects are 

 present. Paris green, if pure, should be used at the 

 rate of from six to eight ounces to 50 gallons of 

 water. In cases where these strengths show any 

 tendency toward burning the foliage the difficulty 

 may be largely overcome by adding from two to 

 three pounds of quicklime to 50 gallons of the mix- 

 ture. A number of exceptions will be found in the 

 classifications of the insects and remedies to be used 

 for the same. Not all biting and eating insects 

 can be readily destroyed by poisons. The peach 

 tree borer, for illustration, eats its way underneath 

 the bark, where it feeds upon the softer tissues of 

 the stems thoroughly protected from any materials 

 of this class. 



Many pests are extremely difKcult to control by 

 any of the above methods, and their damage can be 

 prevented only by the indirect method of crop 

 rotation. In areas devoted entirely to the growing 

 of onions for a number of years, onion insects will 

 come in to such an extent as to seriously jeopardize 

 the crop in spite of all direct treatments that may 

 be employed. The only sensible and rational treat- 

 ment is to stop growing onions for a while until 

 these pests are starved out. The same principle 

 applies in the control of all insects and offers one 

 of the most important arguments in favor of crop 

 rotation, as cited before in Chapter V. 



The value of natural enemies and their possible 

 introduction and encouragement is becoming of 

 more importance in the warfare of insects every 

 year. The dreaded gypsy moth and brown tail 

 moth of the East have very efifectually withstood all 



