318 ANNUAL REPOETS OF DEPARTMENT OF AGRICULTURE. 



the system can be adapted in a way to make poisoning profitable 

 under these different conditions on land which normally produces 

 one-half bale or more per acre. Much valuable information was se- 

 cured also on the exact limitations of profit in boll weevil poisoning. 



The development of dusting machinery has been continued. There 

 are now over 40 different machines on the market, practically all 

 of which were previously tested at the Delta Laboratory. Progress 

 is being made on the development of new types of machines suited 

 to conditions for which no machines are at present available. This 

 has resulted in the recent appearance on the market of the so-called 

 saddle gun or mule-back gun. While this machine is still in the de- 

 velopmental stage, apparently it has much promise of usefulness. 



The studies on the quality of the various types of calcium arsenate 

 on the market have been considerably elaborated and a cooperative 

 project inaugurated with the Bureau of Chemistry. Methods of 

 manufacture are being studied in order to determine the causes of 

 variations in the completed product in relation to its adhesiveness, 

 ease of distribution over the plant, etc. The investigation undoubt- 

 edly is leading to a considerable change in methods of manufacture 

 and a much improved product. 



The chemical inspection is being continued as in the i)ast in co- 

 operation with the Federal Insecticide and Fungicide Board. This 

 includes both the examination of unofficial samples of calcium arse- 

 nate submitted by county agents and the study of official samples 

 taken by inspectors employed by the Insecticide and Fungicide 

 Board. In connection with the latter type of inspection, evidence 

 for court cases is secured whenever the material is found to be unfit 

 for use. 



Studies on the deterioration of stored calcium arsenate extending 

 over a period of several years have just been completed and a manu- 

 script on the subject has been prepared for publication. The inves- 

 tigation has led to important modifications in the kind of containers 

 recommended for the shipment of calcium arsenate, and has done 

 much to standardize the supply. These studies also were made in 

 cooperation with the Insecticide and Fungicide Board. 



An interesting development of boll-weevil poisoning is the fact 

 that in some localities the use of calcium arsenate so reduces the 

 natural enemies of the cotton aphis that the latter becomes seriously 

 injurious to cotton. Investigations are being conducted to determine 

 the best method of control of the cotton aphis in connection with 

 control of the boll Aveevil. Studies are also being conckicted bearing 

 on the relation between the use of calcium arsenate and the possible 

 incidental control of the bollworm. 



Tobacco insects. — The most important addition to tobacco horn- 

 worm control has been the perfecting of a tandem-wheel shaftless 

 type of one-mule two-roAv duster for the application of insecticides 

 to the tobacco plant. The work was begun two years ago and was 

 mentioned in the annual report of last year. Since that time more 

 than 200 acres have been dusted with the experimental model with 

 much better results than could have been obtained with hand dusters. 

 As much as 18 acres has been dusted in a single day, about three 

 times as much as could have been done with a hand duster. A pat- 

 ent to be dedicated to the public has been applied for, and already 

 one of the older manufacturers of dusters has begun the construction 



