WINTER INJURY 267 



late maturity with late cold and in 1917-1918 immaturity and early 

 cold are the distinguishing features. 



Speculation is uncertain but in this case rather interesting. It can- 

 not, of course, be proved but it seems possible that had the rainfalls of 

 1895 and 1917 been exchanged the damage would have been less in both 

 cases; or, had the rainfall of 1915 been combined with the August-October 

 temperature of 1900 and the November minimum of 1904, how great 

 might have been the danger! Out of the 35 seasons covered in Table 

 18, only six have no notable climatic extreme to be recorded. 



Winter Injuries Classified. — Winter-killing of hardy fruits in temper- 

 ate regions, then, may depend on: (1) a lack of maturity in tissues, (2) 

 a lack of ability to resist winter drought conditions, (3) too ready response 

 to short periods of warm weather in the winter. These are listed 

 here in the probable order of their relative importance and frequency, 

 though in any given section the sequence may be changed. In the 

 Minnesota-Dakota section, for example, it is probable that winter drought 

 and absolute cold are more frequently the causes of winter-killing; in the 

 northeast the lack of maturity of tissues is probably the one dominant 

 factor, while farther south much of the winter-killing of buds is the result 

 of the breaking of dormancy by unseasonable warm weather, followed by 

 ordinary cold. 



These classes can be recognized in many cases by the form of the resul- 

 tant injury, though sometimes different causes appear to have nearly 

 identical effects. Crown injury and crotch injury may be related 

 with some certainty to lack of maturity. Killing back of branches results 

 from the same factor, but may be regarded also as a sign of varietal ten- 

 derness or it may be caused by winter drought. Killing of apple fruit 

 buds in northern sections appears to be a result of absolute cold, but with 

 peaches in climates such as that of Missouri it is to a considerable extent 

 induced by ready development before cold weather has passed. Winter 

 sun-scald is a localized manifestation, ordinarily, of a late winter freezing. 

 Trunk splitting is frequently associated with an immature condition and 

 at times with a sudden and considerable drop in temperature. 



The diversity of causes and multiplicity of effects make it quite evi- 

 dent that any attempt at setting definite temperatures as injurious or fatal 

 without regard to other conditions is futile. Though there is a generally 

 accepted belief that — 14°F. is fatal to peach fruit buds, they have been 

 known to survive — 20°F. It is not always the coldest winter that does 

 the greatest damage. Much depends on the character of the preceding 

 autumn, whether it induced proper "ripening" of the wood or forced 

 late growth and on the period at which the cold weather occurred; of 

 course much depends on the treatment accorded any given orchard or 

 tree during the preceding summer and autumn. 



