PESTS OF THE HOP CROP. 123 



the extreme northwest, where the plum or prune crop 

 is such a valuable one. In such cases recourse must 

 be had to extensive spraying, preferably of the plum 

 trees themselves in the early spring, since the lice are 

 infinitely fewer in number at that time of the 

 year, or of the hop crop itself, the earlier the better, 

 after the lice make their appearance. 



As to sjTraying materials, the extensive experi- 

 ments which we carried on at Richfield Springs in the 

 summer of 1887 show plainly the efficacy of the stand- 

 ard kerosene emulsion diluted with 15 parts of water 



FIG. 61. APHIDINE PARASITE OF HOP PLANT LOUSE. 



Greatly enlarged. (From U. S. Department of Agriculture.) 



and of a dilute soap wash made from homemade fish- 

 oil soap. In Oregon and Washington, for some rea- 

 son, the kerosene emulsion has not come into general 

 use. As has been recently shown with such positive- 

 ness, in the case of the San Jose scale and the lime salt 

 and sulphur wash, there is really a difference in the 

 effect of the same insecticide wash on the Pacific and 

 Atlantic coasts. Nevertheless, the decoction of quassia 

 chips, which was so strongly recommended and so 

 frequently used in Oregon and Washington in 1890 

 and 1892, fostered, as has been said, by the efforts of 



