582 ANNUAL REPORT OF THE Off. Doc. 



Dec. 8. On these particular plum trees the examination on Jan. 6. 

 showed from ninety to ninety-seven per cent, of the insects dead, 

 while on the apple trees only forty to fifty per cent, were dead. 

 These results may be due to other conditions than the insecticide, 

 but from the count it appears that this material was nearly suc- 

 cessful on one kind of tree, and a complete failure on another, 

 although applied on the same day and under the same conditions. 



Oct. 5, we sprayed twenty-live apple trees with "Scalecide," made 

 by the J. G. Pratt Co., using one part to twenty-five of water. Exam- 

 ination made two weeks afterward showed that at least ninety 

 per cent, of the scale were dead. On Oct. 10 a block of plum 

 trees were sprayed with the same material and strength, using 

 the same apparatus, and on this lot not over forty per cent, of the 

 scale were dead on Nov. 20. With these varying results it was 

 though necessary to spray more trees for comparison. On Dec. 

 G twenty-five apple and plum trees were treated with the same 

 material at the same strength. An examination on Jan. 5, showed 

 from thirty-five to forty-five per cent, of the scale dead, the result 

 upon apple and plum being the same. Further experiments will be 

 made with these materials, particularly with the last two in order 

 to see if the differences are not due to natural conditions of the 

 insects on the different trees rather than to results of spraying. 

 It must be remembered that from fifteen to forty per cent, of the 

 scale insects may be found dead during the winter, even upon trees 

 that have not been sprayed, and consequently the total percentage 

 of dead individuals given above cannot be attributed to insecticides. 



From these experiments we are forced to conclude: (1) That no 

 hard and fast rule can be formed as to the success or failure of an\ 

 commercial insecticide, as we have had a few fairly successful re- 

 sults and complete failures under the same conditions. It is neces- 

 sary to repeat them several times in order to eliminate the chances 

 of error. 



(2) In the majority of cases the failures or partial failures far out- 

 number the results that would be called even fairly successful. 



(3) It is impossible, owing to varying original conditions and final 

 results to calculate accurately the per cent, of scale insects killed, 

 and the margin of variation may be at least five per cent, on either 

 side of the definite result. 



(4) That the solution of the problem of controlling the San Jose" 

 Scale by means of commercial insecticides is yet to be solved. 



EXPERIMENTS WITH STANDARD HOMEMADE INSECTI- 

 CIDES FOR THE SAN JOSE SCALE. 



By ROSS F. LEE. 



Owing to the great increase of the San Jose" Scale and other scale 

 insects throughout the State, the Division of Zoology of Pennsylva- 

 nia, decided to start a series of experiments with Lime-sulphur-salt 

 mixture and other home-made remedies. There is a great demand 



