36 MANUAL OF FRUIT DISEASES 



signs of injury from low temperatures. But these varieties are 

 not invariably injured ; and on the other hand those varieties 

 omitted from the list are not always free from the trouble. 

 Frost-injury seems to be confined largely to orchards between 

 the ages of eight and thirty years. High-headed, severely 

 pruned individuals of any variety on wind-exposed locations 

 are most liable to the difficulty. Therefore, factors other than 

 the nature of the variety condition the injury under con- 

 sideration. 



The role of frost-injury in fruit crop-production is a promi- 

 nent and important one. Growers of fruits in practically all 

 temperate and even in semi-tropical regions know and fear 

 this trouble. But not every one appreciates the actual damage 

 done in each case. It is only after hard disastrous winters such 

 as were experienced in the East in 1903-1904, 1904-1905 and 

 1906-1907 that general complaints and appeals for help are 

 made. Trees are severely injured and often killed in the ex- 

 tremes of winter temperatures of the northerly sections. In 

 warmer regions late frosts sometimes entail heavy losses. 



Symptoms. 



Frost-injury involves all parts of the tree. Injury to aerial 

 parts only are evident to the casual observer. A reliable symp- 

 tom of fatal injury evident at the end of winter is not definitely 

 known. Trees may appear entirely healthy, but on cutting 

 into the bark above the snow line discoloration in the cambial 

 region will be found. Trees, especially in low spots, affected 

 by frost fail to start in the spring or they may make only a 

 feeble growth. As the season advances they look unhealthy, 

 the foliage is yellow, and finally death of the whole tree ensues 

 (Fig. 8). Often a single branch or one side of a tree only is 

 afflicted. Such trees on closer examination show frost-injured 

 areas or cankers at one or more places (Fig. 9). 



Injuries may occur chiefly on the southwest side of trees at 

 a point midway between the crown and head, or they may be 



