New Yokk Agricultural Experiment Station. 387 



Results. — The results were practically uniform on the two plats. 

 Decided results were apparent after the second application. The 

 treated trees were practically freed from caterpillars by the 2 

 applications. The third application only ensured a little more 

 thorough work. As in the previous year the check trees were 

 stripped of their foliage. 



DISCUSSIONS OF RESULTS AND THE ARSENICALS USED. 



The results indicate that any one of the three insecticides can 

 be depended upon to kill canker worms if properly handled, and 

 that green arsenite and arsenite of lime are equally efficacious with 

 Paris green as poisons for this insect. In these experiments much 

 pains was taken to keep the mixtures well agitated, in order to 

 keep the poison well distributed in the tank and to make the ap- 

 plications thorough. Keeping the mixture well agitated is of 

 especial importance when Paris green is used, as it settles quickly. 



As the arsenicals give practically even results and the foliage 

 was not injured in any case, the principal points to be considered 

 are the ease of application and the cost per pound of the poison. 

 These points may be brought out more clearly by a brief discus- 

 sion of each arsenical. 



Paris green. — The retail price of Paris green is usually from 

 25 to 30 cents per pound. It can be bought in wholesale lots, 

 50 pounds or more, for about 18 cents per pound. The prin- 

 cipal difficulty in using Paris green lies in the fact that it settles 

 so quickly to the bottom of the tank and is so heavy that it is 

 difficult to keep it evenly distributed throughout the tank while 

 spraying. The usual result is that most of the poison is pumped 

 out before the water is half gone." Thus the poison is applied 

 very unevenly. 



Green arsenite. — This arsenical has been previously discussed. 18 

 It costs, retail, 15 cents per pound and can be obtained cheaper in 

 wholesale lots. It is manufactured by the Adler Color and Chemi- 



18 Page 340 of this Keport. 



