200 



MASS. EXPERIMENT STATION BULLETIN 170. 



branches or buds or flowers will be affected; or, again, it may be con- 

 fined to the roots or other portions of the tree. The apple, pear, quince, 

 peach and plum, various shrubs and vines and 

 small fruits are often injured severely both above 

 and below ground from winterkilling, and much 

 loss results to agriculturists. 



There are several types of injury resulting from 

 low temperature which may be easily distinguished, 

 and which occur almost every year, such as winter- 

 killing of the roots, of the trunks, branches, twigs 

 and buds; also injury to exposed roots; to the cork 

 cambium, resulting in exfoliation of the outer bark; 

 and frost blisters, causing subsequent defoliation. 



Winter injuries are not always the result of 

 severe cold, but follow from a combination of 

 factors. Even the temperature of a comparatively 

 mild winter is sufficient to cause much injury to 

 trees and vegetation in general if the preceding 

 summer and fall have been unfavorable for nor- 

 mal plant development. A very dry summer affects 

 the normal growth of vegetation, and if a warm and 

 unusually wet fall follows such a period the plant will go into the winter 

 resting stage under abnormal conditions, and may therefore possess little 

 power of resistance to cold. 



Some of the conditions which underlie winterkilling are as follows : — 

 Severe cold, causing frost to penetrate to a great depth. 

 Sudden and severe cold following a prolonged warm spell in the fall, 

 in which case the wood tissue is tender and immature. 



Conditions which favor a soft growth and immaturity of wood. Various 

 causes may be responsible for this, such as growth in a low, moist soil, 

 too heavy manuring or fertilization, or absence of sufficient sunlight. 



General low vitality, caused by insect i^ests and fungous diseases and 

 lack of moisture in the soil. 



Insufficient soil covering, such as lack of organic matter, light niulching 

 and snow covering in winter. 



Location in unusually windy and exposed places, etc. 



Fig. 71. — Same as 

 Fig. 70, with l)ark 

 removed, showing 

 characteristic sculp- 

 turing. 



Winter Injuries of Roots. 

 During the past decade an unusually large amount of injury has occurred 

 to trees through the northeastern portion of the United States as a result 

 of root killing. Innumerable orchards, small fruit plantations and various 

 ornamental plants have suffered, and forest and shade trees form no 

 exception. This injury has been more severe in New York and Ohio than 

 in New England. The trees most severely affected by root killing are the 

 white pine, black oak, white oak, ash, red maple, white maple, elm, 

 butternut, etc. 



