October, ’24] Campbell: calcium cyanide for wire^orms 
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obtained with the drill, which placed the cyanide in the soil in rows 6 or 
8 inches apart, than with the plow applicator, which placed the cyanide 
in rows 14 to 16 inches apart. 6 
(4) Texture of Soil. Too loose or too compact a soil also seemed to 
be the cause of poor results. 
(5) Depth of Application. This appears to be very important, for 
equally poor results were obtained when the cyanide was placed too 
near the surface and when it was placed too deep. The depth at which 
the majority of the wireworms occur seems to determine the proper 
depth for applying the cyanide. This depth appears to vary throughout 
the season but the habits of the worms have not been sufficiently studied 
so that it can be predicted with certainty. In most of the experiments, 
however, the best results were obtained when the cyanide was applied 
from 4 to 6 inches deep. 
The experiments so far have not determined whether it is best to 
apply the material early in the season, or as late as possible, just prior to 
planting, but indications are that late spring will be the best time. In 
early spring the w r orms are not only more or less inactive, but are fairly 
deep in the soil. When the soil warms up they become quite active and 
feed near the surface, but with the advent of hot summer weather, they 
go deeper in the soil again. Screening of a number of one-foot cross 
sections of soil in the last of February showed that 46 per cent of the 
worms were in the upper 4 inches, 40 per cent from 4 to 6 inches deep 
and 14 per cent from 6 to 8 inches. On May 5, however, 73 per cent of 
the worms were in the upper 3 inches and 90 per cent in the upper 4 
inches. 
During cold weather worms turned up by the plow show very little 
activity, remaining at the surface, often exposed for some time, but in 
warmer weather such worms rapidly work back into the soil. In the 
Yakima Valley early applications also killed many adults which had not 
as yet emerged from the soil. 
To determine how long the cyanide remained in the soil, definite 
applications followed by chemical analyses were made, with results as 
follows: No cyanide could be detected in a wet soil 7 after 2 days when 
150 pounds per acre had been applied and none after 4 days following an 
application of 500 pounds to the acre. In a dry soil 7 a faint trace of 
cyanide could be detected on the fourth day after using 150 pounds per 
6 The use of the applicator on 8 or 10-inch bottom plows, or with a spreading device, 
would remove this difficulty. 
7 The wet soil had more and the dry soil less than the optimum amount of moisture 
for cultivation or planting. 
