13 



Amounts of diemkals ordinarily used in gassing. 



The amounts here recommended are thoroughly effective for the 

 black scale at the proper season, and generally effective also for the 

 California red scale and other armored scales. Where the treatment 

 is designed to be absolutely one of extermination, and the expense is 

 not considered, from one-third to one-half more of cyanide and acid is 

 employed, as indicated in the table following, furnished by Mr. Felix 

 G. Havens, of Riverside, Cal. 



The greater expense entailed by this larger quantity of chemicals is 

 offset by the more effective results and the longer intervals between 

 treatments: 



Excessive amounts used for extermination.C' 



o A fumigation of the orangery of the Department of Agriculture demonstrated that half an ounce 

 of cyanide to the hundred cubic feet kills the eggs, even of the black, purple, and other scales. The 

 results are scarcely comparable to the proportions recommended in the tables on this page, for the 

 reason that in these tables the amount of cyanide is greatly lessened with larger trees, and further- 

 more, that the orangery probably retained the gas more effectually than would be the case with cloth 

 tents. Nevertheless, it is interesting to know that a comparatively inconsiderable strength of 

 cyanide, when applied under the best conditions, will prove thoroughly effective against the eggs as 

 well as the insects. 



59729— Bull. 172—08 3 



