BOLL WEEVIL CONTROL BY USE OE POISON. 6 



KIND OF POISON TO USE. 



In the various studies which have been conducted by the writers, 

 nearly every known type of arsenical has been tested, but the first 

 generally successful results were secured from the use of an im- 

 proved type of arsenate of lead. This was soon replaced by calcium 

 arsenate, and this chemical remains the best which has been found 

 for this purpose so far. Tests were conducted with both liquid and 

 dry applications, and it was found that with the liquid spray a 

 slight degree of control was secured, but not nearly enough to make 

 the operation profitable. 



POISON SPECIFICATIONS REQUIRED. 



When calcium arsenate was first tested it was found that the ma- 

 terial as then prepared was not safe for use on cotton plants, owing 

 to the injury caused by burning of the foliage. This was due to the 

 excessive amount of water-soluble arsenic present. It was found 

 that it was possible to make calcium arsenate without this high per- 

 centage of soluble arsenic, and the type which is now recommended 

 for this work is absolutely safe for use on plants. Not all calcium 

 arsenate, however, is of this safe type. Anyone attempting this 

 work should purchase the calcium arsenate on specifications describ- 

 ing its composition. The specifications advised are as follows : 



Not less than 40 per cent arsenic pentoxid. Not more than 0.75 

 per cent water-soluble arsenic pentoxid. Density not less than 80 

 or more than 100 cubic inches per pound. 



Calcium arsenate was almost unknown as an insecticide when these 

 experiments were inaugurated, and its production had been at- 

 tempted by only a few manufacturers. Recently, however, almost all 

 insecticide manufacturers have undertaken its production. While 

 its manufacture is comparatively simple, some experience is required 

 to produce a thoroughly satisfactory material. Undoubtedly this 

 difficulty will decrease rapidly as the manufacturers gain more ex- 

 perience in the production of calcium arsenate and the quality of 

 the material becomes standardized, but for the present it is still ad- 

 visable to make purchases only on the specifications recommended. 

 If the total arsenic content is too low, the material is not sufficiently 

 poisonous to control the weevil. If the proportion of water-soluble 

 arsenic is too high, plant injury will be the result. Some lots of 

 calcium arsenate have been found which killed the cotton plants 

 within a few hours after application. It is also important to watch 

 the density of the material very closely. If it is too heavy and runs 

 much less than 80 cubic inches to the pound, it is not suitable for use 

 in dry powdered form and will not produce the proper type of dust 



