CONTROL OF ROOT FORM OF WOOLLY APHIS. 39 



Winchester, Va., his object being to prevent the ravages of the woolly- 

 aphis. Following this idea he planted 200 trees, the first tier of main 

 roots being 18 to 24 inches below the surface of the ground in a stiff 

 clay soil. The second year after planting some of the trees began to 

 show signs of distress, while others were growing normally. The 

 third year some were dead, others nearly dead, and others growing 

 normally. 



An examination of the root systems showed the following con- 

 ditions : 



1. The root growth on the dead trees was poor. The roots had made an 



unsuccessful attempt to reach the upper layers of the soil. No new tiers 

 of roots had been pushed out at a higher level in the soil. 



2. The trees in a subnormal condition had succeded in pushing a few roots 



up to the top layers of the soil (PI. VIII). 



3. The deeply planted trees which were growing normally had succeeded 



in pushing the majority of their roots up to the surface layers of 

 the soil. 



When trees are planted deeply only a portion of them will succeed 



in pushing their roots up to the surface layers of the soil. The trees 



which do not succeed in accomplishing this eventually die. Deep 



planting is unnatural, injures the tree, and does not prevent aphis 



infestation. 



SUMMARY. 



Carbon disulphid, in solution at the rate of one-half ounce to 4 

 gallons of water and applied at the rate of three-fourths gallon per 

 square foot of soil, will control the root form of the woolly aphis un- 

 der suitable soil conditions. The liquid is best applied by preparing 

 shallow basins about the tree and should be applied only when the 

 soil is in a moist condition. The solution is best prepared by pouring 

 the carbon disulphid into the water and agitating vigorously. The 

 carbon disulphid thereby breaks up into small globules, some going 

 into solution and the remainder forming a mechanical mixture with 

 the solution. The gas diffuses laterally and vertically only as far as 

 the liquid penetrates and therefore every square foot of infested soil 

 must be subjected to the action of the solution in order to insure 

 complete control. When used at the foregoing rate the carbon disul- 

 phid produced no injury to the roots of apple. The treatment may 

 be made at any time during the growing season except during the 

 period of two or three weeks in the spring when the trees are budding 

 out. 



In orchard practice the solution is best applied by using a power 

 spraying outfit and two auxiliary tanks. 



The advantages of this method are, first, the even diffusion of the 

 liquid and complete aphid mortality in the soil area treated and, 

 second, the safety with which the disulphid can be used. The dis- 



