WINTER INJURY 



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Contributing Factors. — The drying effect, of wind should be considered, 

 as also the effect of cold winds on the temperature of the exposed tissues. 

 Winter killing is sometimes more severe in the three or four rows nearest 

 the windward side of the orchard. Many of the older prune orchards in 

 the northern end of the Willamette valley still showed, 15 years later, 

 the marks of the freeze of November, 1896, in the shape of dead areas on 

 the northwest sides of the trunks, corresponding to the direction of the air 

 drift at the time of the freeze. In many cases of this sort the dead tissue 

 ceases abruptly at the point where snow stood at the time of the injury, 

 suggesting at least that the injury was due to the temperature effect of 

 the wind. The effect of snow on soil temperatures will be shown 

 later. This protective influence evidently is not confined to the soil, 

 as data shown in Table 20 clearly indicate. 



Table 20. 



Temperature Under 10-Centimeter Snow Covering 

 {After Goeppert^^^) 



Consideration should be given, also, to the unequal maturing of 

 tissues on different sides of the tree trunk. Casual observations in 

 autumn have indicated that maturity may be attained more rapidly on 

 one side of the stem than on another. It would follow, then, that a given 

 temperature in autumn might prove injurious to the tissues of one side 

 and not of the other, without the intervention of other causal agents. 

 Furthermore, it should be considered that the temperature a few inches 

 above the soil may be, on clear cold fall nights, 10° colder than is indicated 

 by a shelter thermometer, so that an official temperature record of 20°F. 

 may mean that the tissues at the crown were exposed to a temperature 

 of 10°F. 



Remedial Measures. — In view of the different circumstances under 

 which this type of injury occurs it is probable that not all the factors 

 mentioned are operative in any given instance and that only one of them, 

 if sufficiently intensified, may produce the injury. The one condition 

 apparently requisite to crown rot and to crotch injury is immaturity 

 in the tissues at the point involved. The prospective grower is safe in 



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