i6 INSECTS OF ECONOMIC IMPORTANCE 



and (2) tricalcium arsenate Ca->(As04)2 are the 

 forms that have been used. The latter appears to 

 be more stable and less liable to form soluble arsenic 

 and is therefore safer to use as a spraying material. 

 The calcium hydrogen arsenate when combined 

 with lime-sulphur for summer spraying is likely to 

 give severe burning depending somewhat on 

 weather conditions. The commercial mixtures ap- 

 pear to be a combination of the calcium hydrogen 

 arsenate and the tricalcium arsenate. When com- 

 posed of pure tricalcium arsenate less injury may 

 be expected. Calcium arsenates are high in arsenic 

 content and when manufactured properly may 

 prove to be of much use in spraying operations. 

 At present they are in the experimental stage. 



ArSENITE of ZINC 



Arsenite of zinc ^^ is a white powder and high in 

 arsenic content containing about 40% of arsenious 

 oxide. Tt has been used with success apparently in 

 the Pajaro Valley, Calif., on the foliage of apple, 

 potato and bean. In the East it has proven danger- 

 ous on apple foliage when used alone or with lime- 

 sulphur. In combination w^ith Bordeaux mixture 

 it appears to cause no injury to apple foliage. It 

 is of use in spraying potatoes because of its high 

 toxic quality. 



''Slug-shot" 



This appears to be mostly composed of gypsum 

 and not of much value as an insecticide.^^ 



Bug death 



Is another trade insecticide of little value for it is 

 largely composed of zinc and iron oxids.^^ 



29 Schoene— N. Y. State Expt. Stat., Tech. Bull. 28. 



30 Van Slyke— N. Y. State Expt. Stat. Bull. 165. 

 ?i Smith— New Jersey Expt. Stat., Bull, 214, p. 14. 



