362 Diseases of Truck Crops 



Insecticides 



All animal and insect pests are best controlled by 

 the use of poisonous mixtures applied in the form of 

 liquid sprays or of powders. Insecticides may be 

 classified as internal or stomach poisons, and external 

 or contact poisons. 



(a) Stomach Poisons. Paris green is one of the 

 oldest of stomach poisons. When chemically pure, 

 it is composed of copper oxide, acetic acid, and arseni- 

 ous acid. It destroys cutworms, caterpillars, beetles, 

 grubs, slugs, etc. It should be applied preferably as 

 a liquid, using one pound of the poison and two 

 pounds of lime to two hundred gallons of water. It 

 tends to sink to the bottom of this mixture, unless 

 constantly stirred while being applied. This chemi- 

 cal is often adulterated with white arsenic, causing 

 it to scorch the treated plants badly. Therefore 

 for truck crops the use of arsenate of lead is to be 

 preferred, since it is less liable to scorch the foliage, 

 and it adheres better. Its chemical composition 

 consists of acetate of lead and arsenate of soda. It 

 is applied to the best advantage as a liquid, using 

 about three pounds of powdered arsenate or five 

 pounds of paste arsenate to one hundred gallons of 

 water. 



Arsenite of zinc may also be used. It is a very 

 finely divided fluffy white powder which distributes 

 and adheres well to the foliage. It is intermediate 

 between Paris green and lead arsenate in strength, 

 and it costs less than either. 



