CONTROL OF ROOT FORM OF WOOLLY APHIS. 37 



INJURY TO THE TREE. 



The trees used in the following experiments were of 1-year growth 

 in the nursery and were planted in the spring, three months prior 

 to the experiments outlined below, which were carried out during 

 the height of the growing season. 



4 ounces of sodium cyanid to 4 gallons of water killed the tree in 48 hours. 



The foliage turned brown and dried. 

 2 ounces of sodium cyanid to 4 gallons of water killed the tree in 7 days. 



1 ounce of sodium cyanid to 4 gallons of water injured the tree, as indicated 



by the browning of the foliage to some extent, but it did not kill the 

 tree, which resumed growth later in the season. 

 One-half ounce of sodium cyanid to 4 gallons of water produced no apparent 

 injury nor did it check the growth. Trees treated with this dosage 

 remained normal during the following two years and made a satisfactory 

 growth. 1 



During the following summer, when this block of trees was in its 

 second year of growth, trees other than the ones used in the dosage 

 tests outlined above were treated, with the following results : 



4 ounces of sodium cyanid to 4 gallons of water killed the tree in 8 days. 



2 ounces of sodium cyanid to 4 gallons of water injured the foliage to some 



extent but did not kill the tree. 

 1 ounce of sodium cyanid to 4 gallons of water produced no apparent injury 



nor was there any check in growth. 

 One-half ounce of sodium cyanid to 4 gallons of water produced no apparent 



injury. 2 



It will be observed that the resistance of the apple to sodium 

 cyanid in solution, as in the case of carbon disulphid, depends on 

 the age of the tree. During the extended field tests about 500 apple 

 trees of various ages were treated at the rate of one-half ounce to 

 4 gallons of water with no apparent injury. In excessive doses the 

 same type of injury occurs as results from the employment of large 

 doses of carbon disulphid. 



ADVANTAGES AND DISADVANTAGES OF THE METHOD. 



The only advantage possessed by sodium cyanid as compared with 

 carbon disulphid is its ready solubility in water. On the other hand, 

 its uncertainty in producing aphid mortality in the lower soil levels, 

 together with the extremely poisonous nature of the material, pre- 

 cludes its use in practice. 



USE OF KEROSENE EMULSION. 



PRELIMINARY EXPERIMENTS. 



Kerosene emulsion has been recommended repeatedly as a remedy 

 for the root form of the woolly aphis. Experiments were therefore 

 carried out to determine its efficiency and also to determine what 

 takes place when the kerosene emulsion is introduced into the soil. 



1 See footnotes 1 and 2, page 33. 



2 See footnotes 1 and 3, page 33. 



