CHAPTER XXVII 

 SPRAYING 



405. Significance of spraying. The surfaces of plants may 

 be treated with substances which prevent injury by insects or 

 fungi. A substance that destroys insects is called an insecticide, 

 one that destroys a fungus, a fungicide. The terms sprays, 

 sprayer, and spraying have come to have specific meanings in 

 connection with the control of insects and disease. A spray is 

 a material, a sprayer a machine, spraying the operation ; and the 

 terms cover the use of both liquid and powdered materials. 



Sprays have been used by gardeners and florists for a long 

 time. Formerly the liquids were applied with a syringe and 

 the dust with a bellows. For very many years grape growers 

 have dusted sulphur upon their vines to prevent mildew, and 

 florists have killed plant lice with soapsuds and decoctions 

 of tobacco. 



About 1870 the Colorado potato beetle became abundant 

 and caused heavy losses to potato growers. A cheap poison 

 was needed, and Paris green was found to be very effective in 

 killing the insect. It was mixed with flour or lime and dusted 

 upon the plants, or mixed with water and sprinkled from a 

 watering pot, or spattered upon the plants with a whisk broom. 

 Too much of this poison injured the tissue of the leaves, and 

 the problem became one of distributing the material evenly over 

 the surface in sufficient quantity to kill the insect without in- 

 juring the plant. The success in controlling the potato beetle 



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