156 PRINCIPLES OF PLANT CULTURE 



282. Poisoning. — Destroying insects by poisons or 

 caustics is the method most generally available. The 

 material used is called an insecticide, and if satisfactory, 

 must be destructive to the insects without injuring the 

 plant to which it is applied, or rendering the plant or its 

 products unfit for food. The insecticides in most general 

 use are certain compounds of arsenic (paris green, london 

 purple, white arsenic, arsenate of lead), hellebore and 

 pyrethrum powders, tobacco, kerosene and various com- 

 pounds of soda and potash. With the exception of 

 kerosene and the soda and potash compounds, all of these 

 may be used either as dry powder or with water. 



283. The arsenic compounds are effectual as insect 

 destroyers, even when largely diluted. When applied 

 in water, however, they are liable to injure foliage in 

 proportion to the amount of soluble arsenic they con- 

 tain. Since they are largely insoluble in water, they 

 require stirring to keep them in suspension. 



284. Paris green (arsenite of copper), when pure, is 

 a nearly insoluble compound and may be safely used 

 upon most plants, when diluted at the rate of one pound 

 to two hundred gallons of water. For the peach and 

 nectarine it should be diluted one-half more. Pure paris 

 green dissolves without sediment in ammonia water, hence 

 where adulteration is suspected this test may be applied. 



285. Arsenite of lime, a very cheap arsenic compound, 

 may be prepared by boiling one pound of powdered white 

 arsenic and two pounds of fresh lime in two gallons of 

 water for twenty minutes, stirring occasionally. For use 

 dilute to 400 gallons. This costs only one-fourth as much 

 as paris green. 



286. Arsenate of lead contains less soluble arsenic, 

 remains longer in suspension and sticks to the foliage 



