56 



place, althoug-h several town premises besides those mentioned 

 above were carefully inspected. 



3,931 trees in all had been sprayed with the California wash by 

 my field parties on the premises inspected by Mr. Titus in August. 

 Besides making- a careful general examination of these trees and 

 finding no living scales he critically scrutinized, one by one, 21, 500 

 individuals and found but seven of them alive. There were no 

 crawling young, and none of these living scales had reached the 

 age of reproduction. 



General Summary. 



Four insecticides have been extensively used as winter ap- 

 plications for the San Jose scale in our general orchard work of the 

 past three years in Illinois; hydrocyanic acid gas, whale-oil soap, 

 kerosene emulsion, and the California wash of lime, sulphur, and 

 salt, the first being applied by fumigation and the others as liquid 

 sprays. 



All are efl&cient destroyers of the scale under favorable con- 

 ditions, but the operation of fumigation is practically restricted 

 to comparatively small trees and to comparatively mild and quiet 

 weather. The California wash has an evident advantage in per- 

 sistence of effect, which amounts to an appreciable protection of 

 the tree against immediate reinfestation. 



These four insecticides differ materially in safety, in cost, and 

 in convenienj:e of application. Fumigation with hydrocyanic acid 

 gas and spraying with the California wash are perfectly safe to 

 all trees and shrubs if applied after the old leaves have fallen and 

 before the young leaves have put forth ; whale-oil soap is likely 

 to destroy the fruit buds of the peach if used before these have be- 

 gun to swell in spring; and the kerosene emulsion in strength suf- 

 ficient to insure the destruction of the scale is uncertain in its ac- 

 tion on the more delicate kinds of trees,— the peach especially, — 

 and on those of any kind which are in poor condition. Serious in- 

 jury has occasionally been done to the peach, and in one case to 

 apple, by an emulsion containing only 20 per cent, of kerosene, 

 which is rather below the minimum strength at which this mix- 

 ture should be used for the destruction of the scale. A twenty- 

 five per cent, emulsion, on the other hand, is usually harmless to 

 the apple and pear, but has proved in our work to be highly 

 dangerous to the peach. 



The cost of insecticide treatment includes the expense of the 

 original equipment, that of the materials consumed, and that of the 

 preparation and application of the insecticide. In respect to cost 



