40 BULLETIN 730, U. S. DEPARTMENT OF AGRICULTURE. 



advantages of the method are, first, the huge amounts of water 

 required, with consequent high cost of labor; second, the difficulty, 

 on any but level ground, of preparing basins with level floors, thus 

 insuring the proper distribution of the liquid over the area to be 

 treated; and, third, the wide area of infested roots on older trees, 

 every square foot of which must be treated with the liquid. This 

 last condition precludes the use of carbon disulphid except on small 

 trees with restricted root areas. 



Sodium cyanid at the rate of one-half ounce to 4 gallons of water did 

 not kill the woolly aphis in the lower soil depths even when a super- 

 abundance of solution per square foot was employed. No injury to 

 apple roots resulted when the material was employed at this strength. 

 The only advantage this material possesses, 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. 



When kerosene emulsion is applied to the soil it disintegrates into 

 its component parts; the first inch of surface soil retains the soap 

 and some of the kerosene content; the first 4 inches of the soil retains 

 almost all the remainder of the kerosene. Kerosene emulsion, there- 

 fore, does not kill the aphids in the lower soil levels and the cost of 

 preparing the quantity necessary for soil treatment renders it of little 

 value. The application of this material to apple roots, in the writer's 

 experience, results in severe injury to the tree. 



Deep planting will not prevent woolly aphis infestation and results 

 in the death of many trees so planted, due apparently to the inability 

 of the root systems to function properly under these conditions: 



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