89 



14, receiving- the same treatment except that the insecticide used 

 was the Oregon instead of the California wash, the loss for the 

 same period was 11 per cent. No. 21, sprayed also but once, with 

 15 gallons of water, lost 20 per cent, of its scales in seven days; No. 

 42, exposed to rains for a day and a night, lost in five days 11 per 

 cent, of its scales; and No. 43, similarly exposed, lost 15 per cent. 



The check trees 40 and 41, on the other hand, kept without 

 treatment of any kind, lost within five days but four scales out of 

 five hundred counted. 



It was further apparent from observations made in the field 

 that a brief but hard and dashing rain would detach many more 

 scales than a light rain longer continued, and that a fine misty rain 

 did not loosen the scales at all. 



Practical Conclusions. 



The foreg-oing described observations and experiments go to 

 show that both the Oreg-on wash of lime, sulphur, and blue vit- 

 riol, and the California wash of lime, sulphur, and salt, prepared 

 as described on page 72, are extremely valuable insecticides for 

 winter use in Illinois for the destruction of the San Jose scale; that 

 their effect is produced gradually, and is not altogether complete 

 within a period of three weeks; and that frequent rains will not 

 noticeably diminish their final action even when these come within 

 the first five days after the insecticide treatment. 



Both washes are entirely harmless to any leafless tree, and 

 hence may be freely used in winter (but in winter only) for all 

 kinds of trees, shrubs, and vines. Althoug-h the effect of these two 

 washes as shown by an inspection made ten weeks after the appli- 

 cation, was practically the same — each destroying by that time 

 about 99.2 per cent, of the scales alive at the beg-inning of the ex- 

 periment, there is considerable evidence in my data that the Ore- 

 gon wash acts a little more promptly than the California wash, as 

 shown, for example, by a comparison of effects at the end of a 

 three weeks' period. At this time 8H.5 per cent, of the scales had 

 been killed by the California wash and 94.5 per cent, by the 

 Oregon wash, a difference of 6 per cent, in favor of the latter; 

 and if the comparison be limited to those trees which were not 

 sprayed with water in the earlier days of the experiment, we 

 find that the corresponding ratios are 90 per cent, of destruction 

 for the California wash and 95 per cent, for the Oregon wash. 



A comparison of the insecticide effect of these washes with 

 that of the well-known whale-oil soap solution, two pounds to the 

 gallon, shows that there is a slight difference in favor of the lime 



