134 



AMERICAN FORESTRY 



insects and tree diseases is becoming a 

 more serious problem. Especially does 

 the damage from these sources increase 

 with trees weakened by fires, or grazing, 

 or other causes, or in old over-mature 

 trees. 



Insects are divided into three classes 

 as to mode of attack, namely, chewing, 

 sucking and boring. From the forest 

 standpoint for practical purposes, the 

 two classes of borers and leaf feeders 

 (chewing) are the most important. 



The borers generally work by bur- 

 rowing under the bark and feeding on 

 the living "cambial" tissue between the 

 wood and bark. Spreading out in sec- 

 ondary channels, these insects more or 

 less girdle the tree, or parts of it, and 

 either greatly weaken the vitality of the 

 tree or kill it. 



The leaf feeders, as their name indi- 

 cates, injure the trees by more or less 

 completely eating off the foliage, thus 

 greatly checking growth and weakening 

 the tree; and killing it if repeated over 

 several years. 



The insect enemies are so many, and 

 so varied according to locality, that it 

 is impossible to enumerate these here. 

 Most states maintain entomologists 

 from whom information concerning the 

 insect pests of their states may be ob- 

 tained. 



Of the tree diseases not so much is 

 known. Those that attack living trees 

 generally work by feeding on the 

 cambial layer just under the bark, and 

 appropriating to themselves the nour- 

 ishment which should go into the tree. 



Many of these diseases have two 

 stages and more than one form; that is, 

 they may live part of their lives on a 

 certain tree and part on another plant, 

 and the form on the different hosts may 

 be entirely different and not recognized 

 except after careful study. 



Thus, one of the most threatening 

 diseases which has appeared in some 



time has been the white pine blister 

 rust. This disease lives in one form or 

 young white pine and at other times in 

 another form on the currant and goose- 

 berry. Fortunately, the disease has so 

 far been kept in check by destroying all 

 the currant and gooseberry bushes near 

 any infected localities deprived of its 

 alternate host, the disease cannot spread. 



The chestnut blight is perhaps the 

 most virulent tree disease which has 

 ever appeared. No known remedy has 

 yet been found, and the destruction of 

 the chestnut seems imminent. 



The liability of certain species to dam- 

 age from these causes must be under- 

 stood. Thus, the chestnut bark disease 

 is so virulent in its attack on chestnut 

 as to render it impracticable to favor 

 chestnut as a tree in forest management. 

 Similarly, in many cases the white pine 

 weevil, hickory borer, elm leaf beetle, 

 locust borer, and other insects make 

 inadvisable the favoring of those species 

 in certain localities and under certain 

 conditions. 



These must necessarily modify the 

 forest practice, both in selection of 

 species and especially in taking steps to 

 see that the woods are as little liable to 

 attack as possible. This generally 

 means keeping the woods cleared of dead 

 and diseased individuals, as these are 

 the breeding places for the disease or in- 

 sect. Another important and practicable 

 thing is to protect and encourage the 

 propagation of our insectiverous birds, 

 etc., as these are very valuable in check- 

 ing depredations. 



Poisonous gases, such as produced by 

 smelter works, often will kill all the tree 

 growth in their vicinity. This is of 

 very limited occurence, however, and 

 not often noted. About the only 

 measure possible in such cases is to use 

 the species most resistant to the poisons 

 found. 



(To be continued.} 



WASTE LAND ON THE FARM 



