WINTER INJURY 301 



Protective measures include the use of winter irrigation, thorough 

 cultivation, frost-killed cover crops and windbreaks or shelter belts. 



Many cases of injury from cold during late winter are associated 

 with a breaking of the rest period, resulting in some resumption of growth 

 and an accompanying decrease in resistance to low temperatures. They 

 are brought on by periods of mild weather during late winter. Fruit 

 buds particularly are susceptible to injury from this cause. Buds in 

 certain positions are especially subject to this form of injury. The ending 

 of the rest period in midwinter or spring is related to some extent to the 

 time of its inception in the fall. Consequently factors or practices 

 which delay its beginning tend to protect against the forms of winter 

 inj ury incident to its breaking. Among such practices may be mentioned : 

 Moderatel}^ late cultivation, reasonably heavy pruning, applications of 

 nitrogenous fertilizers and thinning. The end of the dormant period may 

 be delayed somewhat by whitewashing and shading, which reduce heat 

 absorption. 



Most sunscald is attributable to extreme and rapid fluctuations 

 in temperature of the affected tissues. Injuries similar in appearance 

 sometimes are caused by midsummer heat or they may be associated 

 with immaturity coupled with low temperature. 



In general, rapid decreases in temperature are more damaging than 

 more gradual decreases to the same or even to a lower point. A special 

 form of injury due to very rapid temperature decline is trunk splitting 

 or frost crack. 



