14 Department Circular 367, U. S. Dept. of Agriculture 



States Army Air Service pilots. These planes had been adapted for 

 cotton dusting by installing metal dust hoppers in the rear cockpits 

 with an arrangement provided for releasing the dust through the 

 bottom of the fuselage. 



In developing the method of handling the planes so as to distribute 

 the dust properly and in determining the quantity of Paris green to 

 use, flights were made first over open fields, then over dry woods, and 

 finally over various types of mosquito-breeding swamp and lake 

 areas. As the Paris green is effective in very small quantities, it was 

 diluted by mixing it with an inert carrier before it was distributed. 

 For this purpose a fine silicious earth was used in most of the tests, 

 although ordinary road dust and a mixture of flour and lime were 

 employed on a few occasions with fairly good results. 



From these tests it was found that a given area could be covered 

 rather thoroughly with the dust, and that by taking advantage of a 

 light breeze a wide strip could be treated with each trip of the plane. 

 A wind velocity as high as 10 to 15 miles per hour was, however, a 

 disadvantage in making the dust applications, and the operations 

 were usually discontinued when the stronger winds were blowing. 



In addition to the different types of marsh and lake areas treated 

 in the two seasons, applications were made on a section of one of the 

 natural bayous and on a small field of rice. The results of the entire 

 series of tests in the reduction of larvae were variable, owing in part 

 to the failure of the dust to reach all of the area under observation 

 and in part to an unsatisfactory lot of Paris green which was used 

 in a number of the experiments and which proved to have a very 

 low toxicity for the larvse. 



With an experienced pilot, and when careful attention was given 

 to the spread of the dust, no special difficulty was encountered in 

 distributing the dust over the treeless part of the lakes. Further- 

 more, from the single experience in treating rice fields, this type of 

 breeding place appears to be particularly well adapted to control 

 by airplane dusting, because of the absence of trees and other obstruc- 

 tions which interfere with close flying. As had been anticipated, 

 the most difficult conditions encountered were in the heavily wooded 

 areas where the water was protected by dense overhead foliage, and 

 where the planes had to be flown high enough from the ground to 

 clear the tallest trees. Even in such places, however, the dust was 

 found to have penetrated the thick growth and to have reached the 

 water in sufficient quantities to destroy the larvae when enough of 

 the dust had been used to offset the increased wastage. Under such 

 conditions the loss of dust due to adherence to the leaves and to wind 

 drift was considerable. 



The quantity of Paris green used in the experiments varied from 

 about one-twentieth of a pound to several pounds per acre. Ex- 

 clusive of the tests in which the poor sample of Paris green was used, 

 the writers' experience indicates that approximately one-half pound 

 per acre will give a safe margin for the treatment of such places as 

 rice fields and the more open parts of the lakes, the quantity being 

 increased as necessary where the breeding area is protected by a 

 growth of trees and brush. 



The two final tests of 1924 gave particularly clear-cut results, and 

 for this reason were of special interest in showing the possibilities 



