April, '21] DUSTING DISCUSSION 233 



available nicotine than a clay with nicotine added, although you add 

 the same amount of nicotine in each case. 



I would like to know whether any experiments have been conducted 

 with clays and nicotine as well as sulphur and nicotine. 



Mr. Ruth : Sulphur will volatilize by hydrolysis of water. 



Mr. Alvah Peterson : I have some points along this line that may 

 be of interest. During the past season we conducted experiments on 

 various plant lice with nicotine impregnation in the various substances. 

 For the most part we used different kinds of clay and impregnated 

 these with var\4ng amounts of nicotine sulphate. We found as Dr. 

 Aloore has suggested that when we made a two percent, mixture of 

 nicotine sulphate in clay, we obtained, as I recall now, about the same 

 killing effect as when we used a half per cent, of nicotine in clay with 

 addition of ground stone lime. Hydrated lime did not give as good 

 results as stone lime finely ground. We know that when lime is added 

 to a nicotine compound such as nicotine sulphate, it liberates nicotine. 

 This combination gave us a very effective dust for the potato aphis. 



Mr. William Moore : When you add lime to clay (clay is colloidal 

 or almost collodial) it precipitates the clay, flocculates it, I believe they 

 call it in soil chemistn^ Precipitation reduces the surface and also the 

 amount of the nicotine that can be adsorbed so you also have a freeing of 

 nicotine from that source as well. 



President W. A. Orton : You know that we have been doing a whole 

 lot of work lately on the mosaics, one of the most important groups of 

 plant diseases, which are carried from field to field and plant to plant by 

 aphids. It is manifestly evident that control of mosaic diseases is very 

 largely dependent upon aphid control. We have been greatly interested 

 to hear that dust combinations of nicotine with, I think, kaolin or lime 

 are being introduced by the entomologists. I wish we might hear some- 

 thing about that from someone who has had experience. 



Mr. p. J Parrott: I would say, Mr. Chairman, that the control of 

 the potato aphis and the potato leaf -hopper by dusting is largely in the 

 experimental stage, and the situation with regard to these species is not 

 ver\^ different from that of the apple aphids, redbugs and other insects 

 which I considered in my paper. The potato aphis and leaf hopper 

 nymphs are susceptible to dusting preparations containing nicotine. 

 But the selection of insecticides is only one factor of the problem, and 

 as far as these insects are concerned there is a serious need of machinery 

 capable of dusting the undersurfaces of potato foliage, as well as data 

 on the effectiveness of this system of treatment in controlling the com- 

 mon potato diseases. Thorough applications of dust kill a large percent- 



