CHAPTER XV 

 INSECTICIDES AND FUNGICIDES 



The treatment of plants to destroy insect pests and 

 fungous diseases is now so important a factor in the growth 

 of crops that a short description of the compounds and 

 mixtures employed will be of value. No attempt will be 

 made to describe the various insects and fungi or to give 

 the proper treatment for each. All such details including 

 methods of application and proper dilution of spray material 

 should properly be taken up in connection with the pro- 

 pagation and growing of various plants. The present dis- 

 cussion will be limited to the chemistrv of the more common 

 spray materials, noting first the chief characteristics of the 

 pests to be destroyed. Figs. 70, 71, and 72 illustrate the 

 method and results of spraying. 



214. Insects. — The insects which destroy crops are of 

 two kinds: First, those which have biting mouth parts for 

 chewing the plant tissues, such as grasshoppers, caterpillars, 

 and cucumber beetles. Second, those which have a beak 

 or apparatus for penetrating the skin of plant organs and 

 sucking up the juices. They do not chew and swallow any 

 of the tissue proper. The woolly aphis and San Jose scale 

 are examples of these insects. 



For insects which eat plant tissue, it is usually sufficient 

 to sprinkle the surface of the leaves with a poison. This 

 kills the insects when the poison is taken internally. The 

 insects which do not eat tissue but suck out the plant juices 

 are not injured by this treatment. They penetrate the 

 skin for their nourishment and do not eat the poison on the 

 surface. Spray materials which kill by contact are efficacious. 

 They act by destroying the skin of the insects or by clogging 

 up their breathing pores, or by merely repelling them. 



