CONTROL OF ROOT FORM OF WOOLLY APHIS. 31 



AMOUNT OP LIQUID REQUIRED IN THE TREATMENT AND THE INFLUENCE OF SOIL TYPE 



AND SOIL MOISTURE. 



The success of this treatment depends on the one essential, that 

 sufficient liquid be used. Experiments carried out for the purpose 

 of obtaining data on this point demonstrated the general efficiency 

 of three-fourths of a gallon of liquid per square foot of soil area treated. 

 This is equivalent to about one and two-tenths inches of water. 



This quantity of liquid, in the majority of cases in moist soils, and 

 regardless of the soil type, will penetrate to reach the aphids infesting 

 the roots at the lower levels. This condition is due to the difference 

 in the depth of infestation in the various soil types by the woolly 

 aphis. In general it may be said that the root infestation by this 

 insect occurs at greater depths in light soils — for instance, the shale 

 loams — than is the case in heavy soils, such as the clay loams. On the 

 other hand, a given quantity of liquid will be absorbed to a greater 

 depth by a light soil than by a heavy soil. It may be said, therefore, 

 that a given quantity of liquid will penetrate a given soil in propor- 

 tion to the depth of the aphis infestation in that soil. For this reason 

 a standard recommendation can be made as to the quantity of liquid 

 required for all soil types. 



The treatment may be used in either dry or moist soil, but is less 

 laborious in the latter. If the ground is well drained, the best 

 results are obtained after a heavy rain, when the soil is saturated, 

 since a given quantity of liquid will penetrate deeper in moist soil 

 than in dry soil, thereby resulting in a more thorough control. 



When the liquid is applied to dry soil, most of the liquid (when used 

 at the rate of three-fourths gallon per square foot) is taken up and 

 retained by the first few inches of dry top soil. In order to insure 

 the death of the aphids in the lower levels of the soil under these 

 conditions it is necessary to use a much larger amount of liquid per 

 square foot of area treated, with a consequent increase in labor 

 and cost. 



THE PREPARATION OF THE LIQUID AND DETERMINATION OF MOST EFFICIENT DOSAGE. 



When carbon disulphid is added to water, and the mixture is 

 allowed to settle, the carbon disulphid drops to the bottom of the 

 container and collects in a single large globule. By agitation with 

 a broad paddle the carbon disulphid may be broken up into globules 

 which diffuse to every portion of the liquid. Some of the carbon 

 disulphid goes into solution while the remainder forms a mechanical 

 mixture with the water. 



The small amount of carbon disulphid dissolved in water necessary 

 for the success of this method is remarkable. The following experi- 

 ment will illustrate this point: A one-fourth inch streani of water 

 at 60° F. was led to the bottom of a column of carbon disulphid 18 



