Pests and Diseases 67 



dition of a plant which is not healthy, and frequently a 

 reasonably good crop will be matured on a field that is 

 attacked by one enemy only, while if attacked by two or 

 more, it would fail to give a profitable return. 



POISONOUS INSECTICIDES 



The first attempts at protecting plants against insects 

 and diseases were made by combating leaf-feeding 

 insects. Their damage was the more obvious and the 

 method of control required less ingenuity than for handling 

 the sucking insects and for diseases. 



Paris green was among the first of the poisonous insecti- 

 cides to be used and is applicable to all leaf-eating insects 

 and smaller animals. About a teaspoonful should be 

 used to a gallon of water, or a more accurate measure 

 would be to use j pound paris green to 50 gallons of water. 

 The mixture must be constantly agitated ; otherwise, the 

 poison will settle to the bottom and the application will be 

 uneven, resulting in a scalding of some of the plants and 

 the others not receiving enough poison to protect them. 

 Paris green is now little used, the arsenate of lead and 

 other materials taking its place. 



Arsenate of lead usually comes in a paste form, the 

 package usually having printed upon it the formula neces- 

 sary for its use. Generally speaking, 1 to 5 pounds to 

 50 gallons of water will be found to be the correct quantity. 

 It is less caustic than paris green and can be used in many 

 places where the latter cannot. It also comes in a 

 powdered form, when it may be mixed with some inert 

 materials such as flour and air-slaked lime and these be 



