30 BULLETIN 1243, U. S. DEPARTMENT OF AGRICULTURE. 



ARTIFICIAL CONTROL. 



At the outset the problem, of artificial control of the Mexican bean 

 beetle appeared to be a matter of the application of the proper 

 stomach poison to the bean foliage. Some experience had been 

 gained along these lines by State and bureau workers in the West 

 and Southwest. The general conclusion from these investigations 

 was that lead arsenate and zinc arsenite are the most satisfactory 

 arsenicals for the control of the Mexican bean beetle, these being 

 recommended as sprays. 



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INVESTIGATIONS OF 1921. 



ARSENICALS. 



The work for 1921 was therefore planned with a view to learning 

 what results could be obtained in the Southeastern States by these 

 sprays. A number of other arsenicals were also tried, chiefly calcium 

 arsenate and magnesium arsenate. A large series of experiments 

 was conducted with various dilutions of all of these arsenicals, both 

 as sprays and as dusts. After completing the first experiments, it 

 appeared as though lead arsenate and zinc arsenite were promising 

 materials, since check plats were totally destroyed and excellent 

 protection was afforded treated plats. Experiments were continued, 

 however, and it was soon learned that the plant injury caused by 

 these arsenicals makes them hardly worthy of recommendation to 

 the grower, on account of reduced yields. 



Different factors were found to influence this plant injury. 

 Attention was called by Dr. William Moore, formerly of the Bureau 

 of Entomology, and C. M. Smith, Insecticide and Fungicide Lab- 

 oratory, Bureau of Chemistry, to the effect on lead arsenate of the 

 water available in the Birmingham district. Further experiments 

 were performed, and it was learned that lead arsenate is absolutely 

 unsafe for application to bean foliage, even with distilled water, or 

 diluted with hydrated lime and used as a dust. It was also learned 

 that zinc arsenite causes a serious reduction in yield, even though 

 the injury to the plant is not as noticeable as injury caused by lead 

 arsenate. Experiments proved that calcium arsenate is absolutely 

 unsafe for bean foliage without the application of an excess of lime 

 along with the material. These results were also obtained when the 

 materials were used as dusts. 



Throughout all the experiments magnesium arsenate, a commer- 

 cial preparation which has not been generally used on account of the 

 injury to foliage of different kinds of fruit trees, was found to be safe 

 on bean foliage, even though used with the water of the district, 

 which is relatively high in soluble sodium salts. Under conditions 

 of severe infestation in 1921 unsatisfactory results were obtained 

 with dilutions of those arsenicals which were injurious to foliage in 

 the undiluted state. 



Since magnesium arsenate is not generally available to bean 

 growers, and because of the fact that growers in the Southern States 

 were more familiar with dusting methods than with spraying methods, 

 a tentative recommendation was made that calcium arsenate of a 

 high grade be diluted with 9 parts of hydrated lime and be applied 

 to the foliage as a dust. The amount of arsenic in this mixture, 



