CHAPTER 20 



INSECTICIDES AND FUNGICIDES 



BY H. GAKMAN 

 Professor of Entomology, University of Kentucky 



The word insecticide has come to mean any chemical or other sub- 

 stance used to destroy insects that are hurtful or objectionable in any way 

 to man. This definition excludes substances such as sticky fly-paper that 

 may be employed to entrap pests and would, according to some entomolo- 

 gists, exclude also simple deterrents, such as oil of citronella, used to keep 

 insects away by their offensive odors. In a general way, however, every 

 substance employed to prevent the injuries of insects is an insecticide and 

 in this view it does not matter whether or not they kill, deter or entrap. 



The insecticides most used and valued by practical men either kill 

 as poisons when eaten with food, or else destroy when brought in contact 

 with the bodies of insects, in which case they are sometimes called contact 

 insecticides. 



A group of insecticides of which the effective ingredient is arsenic has 

 proved especially popular and useful in suppressing insects which feed by 

 gnawing away and devouring the leaves of plants. 



Paris Green. Of these the one best known and most used is Paris 

 green, Schweinfurth green, or Imperial green, French green and Emerald 

 green. It was first used in the arts, and because of its cheapness and 

 poisonous properties was early tried on the Colorado potato beetle (about 

 1868) proving a very satisfactory means of suppressing the pest when used 

 either as a dry powder or when stirred into water. It contains a little 

 soluble arsenic however, and in water this is liable to burn leaves to which 

 it is applied, hence care must be exercised not to use too much. Four to 

 five ounces of the powder in a barrel of water is commonly regarded as 

 enough ; if more is used a pound or two of freshly-slaked lime may be added 

 to neutralize its caustic effect. ^ 



Arsenate of Lead. Paris green has two defects: Its burning action 

 is often hard to guard against, and its weight causes it to settle quickly 

 when used in water, rendering the spray produced uneven in strength. 

 Stirrers connected with spray pumps obviate the latter trouble, but some- 

 times increase the labor of operating pumps. The addition of lime, as 

 already suggested, lessens the burning action, though the lime may, if care 

 is not exercised, increase the labor of applying. 



Arsenate of lead has neither of these defects. It is practically insol- 

 uble in water, does not burn foliage, and it is so finely subdivided that it 



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