April, ’24] HASEMAN & BROMLEY: CHINCH BUG AND CALCIUM CYANIDE 327 
death line of gas as long as possible and with the least effort and use of 
material. Hydrocyanic acid gas is of about the same weight as air 
and when there is no breeze to scatter it, it will hover over the line of 
flakes whether on the surface of the ground or in a furrow. However, 
at wheat harvest there is usually a great deal of wind so it is necessary 
that this be taken into account and guarded against as well as possible. 
Line Barriers Applied on Surface of Ground 
In our preliminary tests with the surface barriers we used from one 
half pound to four pounds of granular cyanide to sixty linear feet of 
barrier. The smaller dosage applied when there was a six-mile wind, 
killed adults bugs which attempted to cross, for only one hour. The 
heaviest dosage, applied under the same conditions, remained effective 
for from three to five hours and killed some bugs five feet from the line 
due to drifting of gas. These also burned the lower blades of wheat. 
A dosage of one pound to sixty linear feet of barrier on the surface of 
the ground remained effective for only about two hours on the average. 
The drifting of the gas from a surface barrier is too great for most 
effective results. 
Line Barriers Applied in Furrows 
Furrows may be made of various shapes and forms and our results 
show that a narrow, deep furrow gives far better results than do those 
of other types. 
In our first tests we used a hoe and a hand plow to make a shallow 
ditch from one to three inches deep. This showed a decided improve¬ 
ment over the line on the surface of the ground due mostly to the fact 
that it retarded the progress of the bugs and kept them longer in the 
gas area. A very shallow ditch does not help materially in checking 
the drifting of the gas,- but it will keep the bugs busy longer climbing 
out of the gas area. 
A deep furrow made with a plow and rounded out with a post, was 
then used. This provides a definite container for the gas and where 
there is no breeze it should be expected to work well. However, in 
our tests it was found that a broad rounded-out furrow of this type 
allowed the gas to spread out in the furrow, and it permitted the wind 
to blow it out readily. The broad furrow in our tests gave no better 
results than a narrow shallow furrow made by hand. However, it does 
provide for the possibility of combining a mechanical barrier with the 
gas barrier. 
To chinch bug workers it is a well known fact, that normally at 
harvest the bugs move mostly during a few hours of the day and only 
