TREE DISEASES AND INJURIES 279 



Other diseases may in the future warrant similar measures 

 of control. 



Efforts to control the chestnut blight, although pursued for 

 some years involving large expenditures of money, were ill- 

 advised and resulted in abandonment of the work. 



Tree Diseases and Injuries Other than Those Produced by 

 Fungi. — Among tree diseases and injuries not previously 

 considered may be mentioned stagheadedness, root-rot, ab- 

 normal needle shedding, injury by acid fumes ^^ from smelters 

 and other manufacturing plants, bark-scorching and crack- 

 ing, injuries from frost, hail, snow, wind and hghtning. 



In a practical way little can be done to control or prevent 

 these diseases and injuries. 



Protection against frost should be assured to the reproduc- 

 tion of sensitive species by affording shelter in early youth. 

 For such species the shelterwood or selection methods of 

 reproduction are advantageous. Early frosts in the fall and 

 late frosts in the spring are particularly to be guarded against. 

 Injury consists in the freezing of seedlings and young organs 

 on older trees, uprooting of seedlings and production of frost 

 cracks and cankers. 



To prevent injury from bark-scorching, exposure on the 

 southern and western sides of trees and stands, susceptible to 

 the injury and which previously have been densely grown, 

 should when possible be avoided. 



Snow is particularly damaging to young evenaged densely 

 stocked stands of conifers. It can be minimized by the sys- 

 tematic use of thinnings and by employing the selection 

 method in elevated regions subject to heavy snowfall. 



Losses from wind can be reduced by starting moderate, 

 thinnings early and repeating often, by not using reproduc- 

 tion methods which unduly expose a portion of the stand 

 (Hke the seed tree method) and by keeping the trees healthy 



