CHAPTER XVII 

 PROTECTION AGAINST TREE DISEASES 



Fungi. — The tree diseases of greatest importance from the 

 silvicultural standpoint are induced by parasitic plants, 

 principally fungi. Chief consideration will be directed to 

 diseases of this class. 



The silviculturist is interested primarily in parasitic fungi, 

 in contrast to saprophytic fungi since the latter attacking 

 only dead or dying material are not the cause of tree diseases. 



For a comprehensive account of all classes of tree diseases 

 reference should be had to books devoted to the subject such 

 as those by Hartig ^ ^'^^ ^ and Rankin.^ 



Parasitic fungi are able to attack living trees, but must 

 have a suitable opportunity for gaining access. In young 

 trees, before the formation of cork in the bark is accompHshed, 

 fungi are able to gain access through the uninjured bark, if 

 climatic conditions are favorable. Older trees can be attacked 

 only through a wound or opening in the protective bark 

 covering. Such wounds may be created in a variety of ways; 

 as for example by fires, lightning, frost, storms, insects or 

 branch stubs left by natural pruning. With western white 

 pine, branch stubs furnish the principal points for attack; ^ 

 with white fir (abies concolor) fire, frost and lightning are 

 largely responsible.^ 



The presence of fungi is revealed readily by the appear- 

 ance of the fruiting bodies springing from the soil or parts of 

 the tree above the ground. Where sporophores are lacking 

 there may still be fungi within the trees. Swellings, or pitch 

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