258 EXPERIMENT STATION RECORD. I Vol. 40 



and July is of some benefit in destroying the larvae and pupae in the cocoons. 



By far the most valuable practice, however, is the application of such cultural 

 methods as will induce a vigorous and rapid growth in a healthy vine. 



A list of 8 references to the literature cited is appended. 



III. Experiments in the control of the root form of tin- tooolly apple aphis, 

 B. R. Leach (pp. 29— iO). — This is a report of a series of experiments couducted 

 in Virginia during the seasons of 1914 and 1915, the work being based upon 

 results obtained by French Investigators in the employment of carbon disulphid 

 and sodium cyanid in solution against the grape phylloxera. The results have 

 been summarized by the author as follows: 



"Carbon disulphid, in solution at the rate of 0.5 oz. to 4 gal. of water and 

 applied at the rate of 0.75 gal. per square foot of soil, will control the root 

 form of the woolly aphis under 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. BOme going into solution and 

 the remainder forming B mechanical mixture with the solution. The gas dif- 

 fuses laterally and vertically only as far as the liquid penetrates and therefore 

 every square foot of Infested soil must be subjected bo the action of the solu- 

 tion in order to insure complete control. When used at the foregoing rate 

 the carbon disulphid produced no injury to the roots of apple The treatment 

 may be made at any time during the growing season excepl during the period 

 of two or three weeks to 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 arc. tirst. the even diffusion of the liquid 

 and complete aphid mortality in the soil area treated and. second, the safety 

 with which the disulphid ran he used. The disadvantages of the method are, 

 first, the huge amounts of water required, with consequent bigb COSl of labor: 

 second, the difficulty, on any hut level ground, of preparing basins with level 

 floors, thus insuring the proper distribution of the liquid over the urea to be 

 treated; and, third, the wide area of infested roofs 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 0.6 02. to 1 gal. of water did not kill the 

 woolly aphis in the lower ■-oil depths even when a superabundance 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 com- 

 ponent parts; the first Inch of surface soil retains the soap and some of the 

 kerosene content; the first 4 in. of the soil retain almost all the remainder of 

 the kerosene. Kerosene emulsion, therefore, does not kill the aphlds in the 

 lower soil levels and the cost of preparing the quantity necessary for soil treat- 

 ment renders it of little value. The application of this material to apple roots. 

 In the author's experience, results in severe injury to the tree. 



"Deep planting will not prevent woolly aphis Infestation anil results in the 

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

 systems to function properly under these conditions." 



