REPORT OF THE STATE ENTOMOLOGIST I912 83 



THE USE OF OILS ON DORMANT TREES 



Spraying dormant trees with oils, especially mineral oils, is one 

 of the more recent developments of insect control work. The late 

 Dr J. B. Smith, late state entomologist of New Jersey, was one of 

 the foremost advocates of this practice and at one time took the 

 position that petroleum was " harmless to the most tender varie- 

 ties and the youngest trees." It should l)e added that later this 

 pronouncement was modified to '* a reasonably safe, economic 

 and effective material." Injury was noted following petroleum 

 applications, and shortly the miscible oils were placed on the mar- 

 ket and used probably much more generally than was the case with 

 petroleum, either pure or in mechanical emulsions. The great ad- 

 vantage of the miscible oils is that they make possible a nearly uni- 

 form emulsion of known strength and there has been much less 

 apparent injury following their use. The ideal in these latter is a 

 stable emulsion which can be kept indefinitely, diluted to any de- 

 sired strength and which will destroy scale and other insects with- 

 out injuring the tree or plant. Some enthusiasts have almost gone 

 so far as to assert that injury could not follow the use of even 

 large percentages of some of the miscil)le oils. 



Safety a prime essential. A fruiting orchard represents a 

 considerable investment, and we believe that most fruit growers 

 rightly consider the safety of the trees of more importance than 

 the destruction of an insect pest or the prevention of possible 

 injury. The rcmcfly should not be worse than the disease and the 

 treatment should most certainly not jeopardize the investment. 

 We are unwilling to sanction, even by implication, the use of com- 

 pounds which may result in material injury and, in some cases, 

 disaster to the orchard. 



Injury by petroleum. The writer's experience with petroleum 

 and mechanical emulsions of petroleum in 1900 to 1903 inclusive, 

 shows that serious injury might result in the latitude of Albany, 

 especially if the application was made in the fall or in the spring 

 if followed immediately by a spell of humid weather. One fall 

 treatment resulted in such penetration and discoloration of the 

 inner bark that grave fears were entertained for the safety of the 

 trees. A similar condition developed in the s])ring when the spray- 

 ing was followed by several days of foggy weather. 



Others have noted deleterious effects following the application 

 of petroleum to various trees in widely separated sections of the 



