26 



substitute for spraying the manufacturers of pumps and spray materials 

 soon begin to show their opposition to the idea. 



Leaving out of consideration the early practice of dusting trees with soot, 

 ashes, Hme, or road dust, the first scientific experiments in the use of dusting 

 were conducted in the years 1904 to 1908 in the experiment stations of 

 IlHnois, Washington, Missouri and Delaware. In all these experiments 

 the material used was dry Bordeaux and Paris green, or in one or two cases 

 arsenate of lead. In other words the fungicidal agent was copper and the 

 insecticide was Paris green. The results of these experiments prove conclusive- 

 ly that, except in cheapness, the dust method did not give so good results 

 as can be obtained by ordinary spraying methods. In the few cases where 

 arsenate of lead was used in these experiments the codling moth control 

 was fairly good. 



The revival of interest in the use of dust came as a result of the almost 

 universal change from Bordeaux mixture to lime-sulfur as a fungicide for 

 the control of apple scab, or a change from copper to sulfur as the fungicidal 

 agent. With this change the use of Paris green was almost entirely abandoned 

 since it could not be combined with lime sulfur solution without injury 

 to the foliage. 



When the lime sulfur solution is sprayed on a surface it soon disinteg- 

 rates and sets free pure sulfur in a very finely divided state. It has been shown 

 that it is this free sulfur that acts as a fungicide and prevents scab infection. 

 Two facts lead to this conclusion as to the value of pure sulfur as a fungicide 

 when present in a finely divided state; first, the success of Scott's so called 

 self-boiled lime-sulfur for preventing brown rot of peach, and second, 

 Wallace's results in using lime-sulfur in a carbonic-acid gas sprayer. In the 

 latter case the sulfur is precipitated by the carbonic-acid and goes on the tree 

 as finely divided pure sulfur. In Scott's self-boiled lime-sulfur, the sulfur 

 is in a finely divided state caused by the slacking of the lime. From this 

 it was only a step to the use of a finely ground sulfur applied as a dust. 



The first dusting experiments with finely ground sulfur and powdered 

 arsenate of lead at the Cornell University Experiment Station were made 

 in 1911, but owing to the almost total lack of both scab and codling moth 

 in the orchard used the results were practically worthless. The experiments 

 were repeated in 1912 on a small scale but with encouraging results, as may 

 be seen from the following table : — 



Treatment Scab Codling Moth Curculio 



% % % 



Untreated 9.0 37.0 73.0 



Lime-sulfur solution 0.7 5.7 5.2 



Dust mixture 0.5 1.3 6.0 



