February, '22] headlee : contact dusts . 81 



SUMMAR\ 



The following conclusions may be drawn from the data contained in 

 this paper; — 



(1) That proper dust carriers impregnated with a 2% nicotine are as 

 effective in control of the pink and green aphis on potatoes as is nicotine 

 delivered in a liquid form ; 



(2) That nicotine delivered as a dust has the following disadvantages — • 



(a) The period of kill is much longer than that necessary for nicotine 

 delivered as a liquid, thus rendering the work of the dust liable to serious 

 interference by rainfall; 



(b) The cost of controlling aphis with nicotine dust is materially 

 larger than the cost of controlling it with nicotine delivered as a liquid. 



(3) That the advantages of nicotine delivered as a dust are primarily 

 concerned with the increased speed in covering large acreages and the 

 freedom from the necessity of a nearby water supply; 



(4) That there occurs in all carriers, with which the writers have 

 experimented, a tremendous waste of nicotine; 



(5) That the improvement of nicotine dust is to be sought in the more 

 rapid evolution of the 2% or less of nicotine, which is within the range 

 of reasonable practice, or in the delivery of such nicotine as is evolved 

 in close contact with the bodies of the lice, or in developing along both 

 these lines. 



Mr. William Moore: Last year I pointed out that nicotine may be 

 absorbed by clay. Professor Headlee 's work proves that this actually 

 occurs. His results apply to his clay, but not to other clays. I have 

 on my desk 6 or 8 different clays; one from Professor Headlee, another 

 from Professor Sanders, etc. I have been testing them in different 

 ways, not particularly from the standpoint of nicotine, but in other 

 ways. Professor Headlee 's does not absorb nicotine as much as some 

 of the other materials. The most interesting clay from our point 

 of view is one from Georgia; I have 2 vials here that I will pass around. 

 They have both the same nicotine content made up according to one of 

 Professor Headlee's formulae and contain calcium oxide. In the light- 

 colored clay, if you will smell it, you will find little or no odor of nicotine. 

 There is 2% there but you cannot smell it. The other sample is Pro- 

 fessor Headlee's clay, and the odor of nicotine is quite noticeable. The 

 white clay comes from the south and ties up the nicotine tight, even 

 in the presence of calcium oxide. 



Mr. W. E. Britton: I would like to ask Dr. Headlee if he has tried 

 it with potatoes? 



