256 ANNUAL REPORT OF THE OfE. Doc. 



from him declares tliat it is impossible to hurt lieu Davis no matter 

 how much oil jou i)ut on. 



Mr. John Repp, of Glassboro, N. J., used 1,000 gallons of oil, undi- 

 luted, during the winter of lOOO-'Ol, without hurting a tree; and his 

 case is not exceptional. 



In the peach district of North Jersey the crude oil, used in a me- 

 chanical mixture with seventy-five per cent, of water, finds most 

 favor, and this seems to be the result of experiments made on peach 

 by others. 



In a mechanical mixture containing twenty-five per cent, of oil, 

 each particle of oil is accompanied by three particles of water, and if 

 the spraying be as carefully done as with undiluted oil, the same 

 amount of oil is made to cover four times as much surface. As the 

 water evaporates or is absorbed, the vaseline and parafiSne remain; 

 but the coating is only one-fourth of what it would be were the oil 

 applied pure. 



It must be remembered that the oil is the killing agent and there 

 must be enough to kill the insects. The water simply spreads the 

 same amount of killing material over a larger surface. The evidence 

 seems to be in favor of the effectiveness of the twenty-five pfer cent, 

 mixture and its safety on trees. It may pay the careful man to ex- 

 periment a little, especially as for this a lower grade oil may be used. 



It makes a difference on peach as to the time when the oil is ap- 

 plied. Trees treated in January have been killed where others in ad- 

 joining rows, treated in March, were unhurt. Bark completely dor- 

 mant is ijrobably more absorbent than that in which the sap is ris- 

 ing. On apple, pear or plum, it makes little difference at what time 

 of the winter the application is made. Fruit buds will not be harmed 

 by any reasonable covering. Yet I would not recommend treat- 

 ment to be made before January. So I would prefer to have trim- 

 ming done after the spraying, for if done before, the cut surfaces 

 would absorb a certain amount of oil. If the cutting is close to the 

 branch this absorption may cause injury; but if one-half to one inch 

 stubs are left, no harm will be caused and the trimming may be done 

 before the spraying. 



As to the price of the crude oil, that has varied from season to 

 season and will vary in Pennsylvania in proportion to accessibility. 

 In New Jersey, the Standard Oil Company demands thirteen cents 

 per gallon and gets it. For this they furnish a green oil, — Insecticide 

 oil they call it, — that tests forty-four degrees or very close to it. In 

 Ohio, oil testing as low as thirty-five degrees has been safely used in a 

 twenty per cent, mechanical mixture. I would be afraid of oil so low 

 in grade; but forty degrees or possibly thirty-eight degrees might be 

 safe in a twenty-five per cent, mixture if there is a material difference 

 in price. 



