104 GENERAL CONSIDERATIONS 



tobacco extract, and a standard remedy for scale in- 

 sects on fruit trees is to cover them with a tent and 

 fumigate with hydrocyanic-acid gas. 



Spraying for insects and fungi has now become so 

 important a part of the best farm practice in the 

 production of many crops that the subject demands 

 a little fuller consideration even in a work of this 

 kind. Spray pumps for applying insecticides and 

 fungicides are now on the market in almost every 

 conceivable form and size, from the little hand atom- 

 izer with a reservoir holding a quart or less to 

 powerful machines with pumps run by gasoline 

 engines and tanks holding hundreds of gallons. 

 Spraying is now a recognized necessity in the pro- 

 duction of nearly all tree fruits and of many vege- 

 tables. It is almost universally used for potatoes, but 

 is too expensive to be employed for most other ordi- 

 nary farm crops. Tobacco and cotton growers usu- 

 ally apply insecticides in the form of a powder. 

 The substances mostly used for spraying are, first, 

 the arsenic compounds, Paris green, London purple, 

 white arsenic, and arsenate of lead. These are the 

 recognized remedies for biting insects. Second, the 

 contact poisons used for sucking insects: kerosene, 

 either as the mechanical mixture with water or the 

 emulsion, whale-oil soap solution, resin-lime mixture, 

 and tobacco extract. Third, various copper com- 

 pounds used as fungicides. The most important by 

 far is Bordeaux mixture. Paris green is often 

 added to Bordeaux mixture, thus affording protec- 

 tion from the biting insects and fungi by the one 

 spraying. Fourth, sulphur in suspension or potas- 



