21 



and the openings at the ground are closed. The mate- 

 rials for generating the gas must vary in quantity with 

 the size of the tree, and the thickness of its foliage. The 

 time necessary to destroy insects ranges from fifteen to' 

 forty minutes. Mr. Coquillett thinks the best time to 

 apply gas is at night or during cool and cloudy days 

 when the life processes of the trees are least active. 



It is not likely that this method of treating trees will 

 soon be employed for large shade trees ; for small ones, 

 for nursery stock, and for some fruit trees, it is admira- 

 bly adapted, and I have called attention to it here be- 

 cause it will doubtless be found in special cases to be the 

 most convenient means of checking injury. Those who 

 may be especially interested in the process will find an 

 excellent condensed account of it in Vol. VI, No. 2, p. 

 176 (1893) Insect Life, printed by the Department of 

 Agriculture at Washington. 



Many other ways of treating trees for injurious insects 

 have been advocated, some good, others of no value 

 whatever. Among the latter may be mentioned the plan 

 of boring holes in the trunks of trees and filling them 

 with sulphur. Tarred bands are sometimes employed to 

 prevent the ascent or descent of injurious insects along 

 the trunks. Whether the bands' prove of value or not 

 depends of course upon whether the insect has other 

 means of getting to the leaves than by creeping up the 

 trunk. They can be of little use in checking the injuries 

 of such pests as fly to the leaves, though they have some- 

 times been recommended and used for such species. For 

 the canker-worm and some others which habitually creep 

 up the trunk the tarred bands can in some cases be used 

 profitably, but even for these spraying, if practicable, is 

 the better treatment. When bands are used the tar 

 must be kept from the trunks by strips of tin, otherwise 

 it may injure the trees. Bands of straw, old carpet, or 



