Remedial Measures and Insecticides. xxix 



for the foliage of a tree will suffer serious injury if the tree is left 

 covered with an air-tight oiled tent for half an hour in sunlight, 

 without the gas being present. Having ascertained this fact by 

 experience, the foreman in charge of the Board's outfit refrained 

 from covering trees until the sun had sunk from sight on any but 

 cool, dull days. The great majority of the trees treated have been 

 fumigated after sunset. The ideal night for fumigating is quiet, 

 cool, and moonlight, and without dew.' 



It is evident, from the above, that the period available for this 

 process is somewhat limited. However, when only a few trees 

 have to be treated, the hour immediately preceding nightfall will 

 be ample for the purpose. I have personally found no ill effects 

 following the operation when performed on dull, cloudy days, when 

 the sun is entirely obscured. 



Although hydrocyanic acid gas will certainly kill every insect 

 — and even their eggs — if used in sufficient strength and for a 

 sufficient length of time, both the necessary strength and time will 

 be found to vary with different species of insects, and must be 

 made the subject of careful experiment. I find that OrtJiegia 

 insignis is a very difficult insect to kill, and requires a double 

 strength of gas, continued for fully three-quarters of an hour. 



Mr. D. W. Coquillet, one of the first to employ this process, 

 gives the following directions for making an air-tight tent: * — ' The 

 material commonly used in the construction of the tent is what is 

 known as blue or brown drilling. A few persons have used 

 ducking instead of drilling, but this is much inferior to the latter ; 

 in the ducking the threads extend only lengthwise and crosswise, 

 whereas in the drilling they also extend diagonally — this belonging 

 to the class of goods to which our merchants apply the term 

 " twilled " — and for this reason the drilling is both stronger and 

 closer in texture than the ducking. 



* After the tent is sewed up it is given a coat of black paint, as 

 it has been ascertained that tents treated in this manner last longer 

 than those which have been simply oiled with linseed oil. Some 

 persons mix a small quantity of soap-suds with the paint in order 

 to render the latter more pliable when dry, and therefore less liable 

 to crack. Instead of thus painting the tent some persons simply 

 give it a coating of size. Sometimes a small quantity of whiting 



* U.S. Department of Agriculture (Division of Entomology). Bulletin^ 

 No. 23. 



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