342 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 17 
tion to do so, when the gas was no longer effective. The percentage of 
kill was estimated at 90% to 100% in these three towns. 
Preliminary tests by Professor F. L. Hisaw, Kansas State Agricultural' 
Experiment Station, indicate that calcium cyanide might be effectively 
used in the eradication of the pocket gopher. Doses of one and two 
ounces were used. The dose was placed in the main run through ah 
opening made with a trowel. These holes were always closed after the 
dosage was administered. In these tests only isolated runs were used 
and only one dose was put in a run. 
Calcium Cyanide dust was tried out in a few holes but proved not to 
have any advantage over the flakes. One hundred holes were given, 
two ounce doses. In ninety-four of these successful kills were made, 
or about 94% effective. In 187 holes a one ounce dose was used. 
Of these, 21 holes were later found to be plugged indicating that the 
gopher was not killed. In the remaining 166 the treatment was suc¬ 
cessful, giving a killing percentage of about 88%. Professor Hisaw feels 
that the holes plugged were for the most part done before gas could be 
generated from the flakes. He found that his best results were ob¬ 
tained in the spring when the soil was moist, while his poorest results 
were in the fall when the ground was dry. From this he concludes 
that the gas generation depends on moisture in the soil. He was able 
to detect the gas in the run 15 feet from the opening but no quantitative 
tests were made. 
These tests in the destruction of pocket gophers are preliminary and 
further work is necessary before safe conclusions can be made as to 
effectiveness under various conditions and the proper dosages to use. 
Conclusions 
Calcium cyanide when used at the rate of 1 ounce to each burrow was 
90% effective or better. When used at the rate of 1 ounces total 
kills were obtained. 
The burrows need not be closed, thus making an appreciable saving in 
time and labor. 
The moisture in the air liberates hydrocyanic acid gas which remains 
in the burrow for several hours diffusing in all directions. The prairie 
dogs are killed in their attempt to come through this curtain of toxic 
gas, very small amounts proving fatal. 
Temperature apparently is not a limiting factor in the use of calcium 
cyanide providing the inmates of the burrows are active. 
Preliminary experiments indicate that calcium cyanide may also be 
used for the destruction of pocket gophers. 
