164 Bulletin 155. 



reason, the trees have been killed. l*robabh- the best time to use kerosene 

 in any strenjj^th is on a brij^ht sunny day when the conditions favor a rapid 

 evaporation of the kerosene. Pure kerosene should not be used without an 

 appreciation of the fact that the results may prove fatal to the plants treated 

 with it. 



Of the different solutions and mixtures used in this series of 

 experiments, it is evident that, all things considered, No. 4 or 

 20 per cent kerosene and 80 per cent water, is the most satis- 

 factory. While this was fully effective in destroying the scales, 

 the foliage remained in good condition. This result corroborates 

 our experience (in Bulletin 144) of last year. Some of the stock 

 which was treated with the 20 per cent mixture was examined 

 by Mr. Slingerland, wlio pronounced all the scales to be dead. 



Conclusions from Our Experience. 



Practicability of spraying. — The practicability of spraying for 

 San Jose scale will depend entirely upon conditions. In the case 

 of fruit trees or ornamentals, permanently set, which have not 

 already become weakened from the effects of the scale, it would 

 seem, in the light of the evidence at hand, to be an entirely 

 feasible operation and if thoroughly done, there can be little 

 doubt as to its effectiveness ; but spraying cannot be recom- 

 mended for nurser}^ stock. When the trees are so close together 

 as they are in the nursery, it is impossible to spray with sufficient 

 thoroughness to insure complete success, and the possibility of 

 distributing the scale on trees thus sprayed becomes too great to 

 warrant such a method of treatment. 



When to spray. — From the fact that the scales are probably 

 more susceptible to the action of insecticides during the period of 

 activity than they are during the winter months, it follows that 

 a weaker insecticide can be used in the summer than during the 

 winter ; and so far as the use of kerosene is concerned, the evi- 

 dence at hand seems to show that plant life is little, if any, more 

 liable to injur}' from it when in an active state of growth than 

 when dormant. Accordingly, the summer season would seem to 

 be the preferable time to spray if kerosene in any form or 

 strength be used. Professor J. B. Smith recommends the use of 

 pure kerosene during the middle of a clear sunshiny day in Sep- 



