APPLE DISEASES 43 



growing season, will, if a severe winter follows, be seriously 

 affected by low temperatures. A dry summer followed by a 

 warm, wet fall makes a tree more susceptible to cold than it 

 otherwise would be. Late cultivation and excessive nitrogenous 

 fertilization forcing late succulent growth tend to an unripened 

 condition of the trees, rendering them susceptible to early win- 

 ter-injury (crown-rot). Sun-scald, however, is not induced by 

 these conditions. The topography, type of soil, and methods 

 of orchard management are factors influencing the severity of 

 frost-injury. 



Control for frost-injury. 



From the foregoing remarks and discussion it seems advisable 

 to reiterate in discussing control the following points with 

 reference to winter-injury : (1) that while some varieties of 

 apples are more susceptible to cold than others, none are im- 

 mune; (2) all parts of a tree are liable to injury, and these 

 injuries are referred to according to the part affected, as root- 

 injury, crown-rot or collar-rot, black-heart, crotch-injury and 

 sun-scald ; these are forms of winter-injury, whereas spring 

 frost affects the buds, blossoms and young fruits ; (3) low tem- 

 perature injury is essentially a desiccation-proccess, resulting 

 chiefly from the sudden withdrawal of water from the cell 

 during a sudden drop in temperature ; (4) succulent immature 

 tissues suffer more than properly matured tissues ; (5) injured 

 bark is inhabited by fungi which may enlarge the wound, pre- 

 venting it from healing ; (6) trees on low, wet soil suffer most ; 

 (7) a dry summer acts detrimentally, and if the autumn is wet, 

 succulent tissue is developed ; (8) injudicious nitrogenous 

 fertilization and cultivation also favor winter-injury. 



It is recommended : (1) that in planting, only those varieties 

 best adapted to the particular soil and environment be selected. 

 (2) Orchards should be cultivated thoroughly in the earlier 

 part of the season, but the operation should cease in time to 

 allow trees to mature thoroughly. (3) A cover-crop should 



