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REDUCING WINTER INJURY TO TREE FRUITS 



W. J. Lord, Department of Plant and Soil Sciences 



Pomologists in the early 1900 's considered winter injury to roots to be 

 a major problem of tree fruit production in northern growing areas. 

 Nevertheless, root-kill of fruit trees apparently has occurred only twice in 

 Massachusetts during this century. Reportedly, it occurred during the 

 severe winter of 1903-04 and it did occur in the "open-winter" of 1978-79. 

 Much more frequent in Massachusetts is injury to apple tree trunks asso- 

 ciated with winter freezes or early-winter pruning. 



Two types of damage occur to trunks of fruit trees. The first occurs 

 in midwinter at the time the low temperature is encountered. The tissue in 

 the trunk contracts unequally and the trunk simply cracks open (Southwest 

 injury). The second type is actual death of the cambium layer in the trunk. 

 In the spring xylem layer swells but the cambium has not laid down new cells 

 for expansion. The bark splits away from the trunk as a result. The latter 

 type of damage, which is generally associated with early pruning, causes 

 more trouble since it involves actual death of tissue. 



Southwest injury on both apple and peach trees can be reduced by appli- 

 cation of white latex paint to the southwest side of the tree trunks 

 including the base of the lower scaffold limbs. Use only latex water 

 soluble paint. Do not use oil or lead-base paints soluble in paint thinner 

 or turpentine because they can injure trees. Whitewash, a mixture of lime 

 and water, can be substituted for white latex paint, but durability is poor 

 and it may not last through the winter. 



A delay in vegetative maturity (the physiological stage where deciduous 

 fruit trees cannot be forced to resume growth if defoliated) will delay 

 acclimation to low winter temperatures. Factors which delay or prevent 

 tissue maturity and cold acclimation include high nitrogen nutrition, late 

 cultivation and irrigation, early defoliation, heavy cropping, not picking 

 fruit on trees, and early pruning (before Christmas). 



Rate of decline in temperature during the Fall can affect cold 

 resistance even though the same minimum temperature is obtained. A slow 

 decrease allows acclimation to occur, whereas a rapid decrease reaches a 

 level too low too quickly for acclimation to occur. Optimum temperatures 

 for acclimation are 25° to 30° F. Keep a record of minimum and maximum tem- 

 peratures, beginning November 1. Delay pruning until February if there have 

 not been 25 days with minima of 28° F or lower by December 25. Do not prune 

 within 10 days following maxima of 55° F or more that occur before 

 Christmas. 



Pruning immediately prior to a freeze greatly increases injury to the 

 tree. The fresh cut apparently stimulates cellular activity and/or creates 

 a strong sink (attraction) for growth hormones, both of which deharden the 

 tissue. Therefore, listen to weather forecasts and stop pruning if a severe 

 cold front is on its way. Prune old apple trees first and do not prune 

 young trees before late February. Leave for late February and March the 

 pruning of all trees that bore especially heavy crops, and those that were 

 weak or had reduced leaf surface for any reason. 



