44 BULLETIN 1243, U. S. DEPARTMENT OF AGRICULTURE. 
MAGNESIUM ARSENATE. 
Magnesium arsenate has proved to be the least toxic to the bean 
plant of all the materials tested, and it is at the same time toxic to 
the bean beetle. For two seasons no appreciable injury has resulted 
from its use in 134 treatments in the field. 
As a spray at 2 pounds per acre with caseinate of lime, it has given 
excellent control. Rain water is not necessary; well water and 
water from streams do not cause injury to foliage, even though the 
content of sodium salts is relatively high. When magnesium arsenate 
was used, increases in yields generally resulted, but slight reductions 
occurred in a few experiments when bean beetle injury was very 
hght. 
“Experiment 6 (Table 11) gives a good idea of the merits of this 
material in comparison with zine arsenite and basic lead arsenate, 
and the relative merits of the latter in comparison with calcium 
arsenate are shown in experiment 7 (Table 11). The check plat in 
experiment 6 was completely destroyed, while the adjacent plat 
treated with magnesium arsenate remained green and bore a good 
ecop., (BIIXIE AS BS 
Magnesium arsenate is also safe for use as a dust. On account of 
poor physical properties it should be diluted with from 1 to 5 parts of 
hydrated lme, depending on the infestation. Further work with 
this material as a dust is necessary. 
This arsenical, as at first placed on the market, was very high in 
water-soluble arsenic content, but the method of manufacture has 
been improved and all the results reported herein were obtained with 
a high grade of material which did not exceed 0.13 per cent water- 
soluble arsenic content, expressed as metallic arsenic. The toxicity 
of this material to the Mexican bean beetle compares very closely 
with that of calcium arsenate. Caseinate of lime as-a spreader, 
added at the rate of half as much by weight as the arsenical, may be 
used with this material when applied as a spray. 
BASIC LEAD ARSENATE. 
Basic lead arsenate is probably the safest commercial material 
for use on bean foliage when mixed with rain water. It does not 
cause injury to foliage when used as a dust. Its low toxicity to the 
bean beetle makes it very undesirable. In one instance 90 per cent 
of the field treated with this material was destroyed, and could 
hardly be distinguished from the untreated field. Laboratory- 
prepared material gave similar results. In other instances, under 
conditions of light infestation, this material gave sufficient protection 
and yields were notably increased. in one experiment this material 
was used at the rate of 4 pounds per acre, as a spray, without injury 
to the bean foliage. Further experiments are necessary to determine 
the degree of control which can be obtained at this rate of application. 
Basic lead arsenate is the commercial basic lead arsenate such as 
is used in certain districts of California, and is termed ‘4, 1, 3, 1—-lead— 
hydroxy arsenate, Pb, (PbOH) (AsQO,),, H,O”’ by McDonnell and 
Smith.?® 
’ Jour. Amer. Chem. Soc., vol. 38, No. 10, October, 1916, p. 2030. 
