E.\T0.MOL0(i\" AM) PLANT QUAItAXTI.NK 
57 
92 percent. There was apparentlj- no correlation between boll weevil mortality 
and percentage of water-solnble arsenic pentoxide, or between the mortality 
and anj^ of the chemical and physical characteristics of the calcium arsenates, 
such as free lime, molecular ratio, and particle size. Just what differences 
in method of manufacture or what physical or chemical qualities of the calcium 
arsenate cause this difference in toxicity has not been discovered. 
SOIL INJURY FROM CALCIUM ARSENATE 
The injurious effect to certain crops following the use of calcium arsenate 
in boll weevil control was tirst observed in eastern South Carolina more than 
10 years ago. In general the soils where injury was noticeable were light, sandy 
soils of low fertility, and the most striking cases of injury were in fields where 
more than normal amounts of calcium arsenate had been used. The crops most 
seriously affected were the legumes, such as cowpeas and soybeans, oats, and to 
a less degree cotton. Although no cases of soil injury have ever been reported 
or observed in the Delta sections of Louisiana and Mississippi, where calcium 
arsenate dust has been used for boll weevil control more extensively and for 
a longer period than anywhere else, an experiment was started at Tallulah 
iu 1931 by applying calcium arsenate to one plot of soil at the rate of 400 
pounds per acre and comparing the crops planted on it with the crops on the 
adjacent plot that had not received any calcium arsenate. The applications of 
calcium arsenate were continued annually for 5 years or until a total of 2,000 
pounds per acre had been applied, an amount in excess of what would be 
applied iu 100 years for boll weevil control under ordinary farm practices. The 
average yield for the 6-year period since the experiment was started was 
1,827 pounds of seed cotton per acre for the treated plot and 1,826 pounds for 
the untreated plot. So far as cotton production on this Delta soil is concerned 
there seems to be no danger from the continued use of calcium arsenate. How- 
ever, soybeans and cowpeas are seriously affected by large quantities of calcium 
arsenate on this soil, as most of the plants soon died on the treated plot. 
In Mississippi the study of the effect of calcium arsenate on seven major 
soil types and crops grown on them has been continued. Plots of each soil 
type received calcium arserate at the rate of 50, 100. 20O, 400. 800, and 1,600 
pounds per acre in April 1935, and no arsenic has been added since that date. 
The germination and survival records for corn, cotton, and soybeans in the 
spring of 1937 show less injury than in the 2 preceding years. The same 
is true for the winter crops, Austrian Winter peas, hairy vetch, and oats. 
The yield of cotton and corn has not been materially reduced on any of the 
seven soils except where applications of 1,600 pounds of calcium arsenate per 
acre were made. The yields of Austrian Winter peas, oats, vetch, and soy- 
beans have been reduced where 800 and 1,600 pounds of calcium arsenate per 
acre were applied. The effect of excessive quantities of calcium arsenate varied 
considerably with the different soil types. The Houston soil, black clay from 
the prairie section, is the most resistant to arsenical injury ; and the Norfolk 
and Cahaba. light-colored, sandy soils are the least resistant. The yields and 
plant survival records indicate that the soils are recovering from the arsenical 
injury, rhemical analyses of the different soils treated with varying dosages 
of calcium arsenate showed that the range in decrease of water-soluble arsenic 
from 1935 to 19.36 was from 23 percent to 80 percent. The maximum quantity 
of arsenic (^As.O;) found in corn, cotton, and soybean plant grown in the 
arsenic-treated soils was 5.8, 10.0, and 8.0 parts per million, respectively. 
COTTON FLEA HOPPER 
Better control of the cotton flea hopper was again secured at Port Lavaca, 
Tex., by dusting with mixtures of arsenicals and sulphur than with .sulphur 
alone. Mixtures of 10 percent of p-iris green and 90 percent of sulphur and of 
20 percent of calcium arsenate and 80 percent of sulphur were about equally 
effective, and both mixtures gave much better control than suliihur alone. 
Excessive rains during the latter part of June and July in 19.36 caused the 
cotton to shed the greater part of the bolls and considerably reduced the yield, 
but even with adverse conditions profitable gains were made by controlling 
the flea hopper. As the mixtures of arsenicals and sulphur are also of value 
against the boll weevil, leaf worm, and other cotton insects, it is expected that 
their use will reduce the cost of control where .several insects occur together. 
Further exi>eriments are needed to determine the best proportions of arsenic and 
sulphur to use under different conditions. Since the finding last year of the 
two cotton flea hopper egg parasites Annphcfi nuoniocrrus Gir. and Enjthmclmf, 
n. sp., studies have been continued of their distribution, abundance, and life 
