COLD INJURY TO PEACH TREES 



William J. Bramlage 

 Department of Plant and Soil Sciences 



In a talk given last year in New Jersey (Horticulture News ^7 : 26-34), 

 Dr, E.F. Savage described some very interesting findings in Georgia about 

 cold injury to peach trees. 



Growers in the Coastal Plain area of Georgia have always been plagued 



by the very short life of their peach orchards the average life of trees 



there is only 8 years. Many years of investigations showed that nutrition, 

 diseases and nematodes all may play a part in this problem, but the basic 

 cause was not uncovered. However, recent findings seem to have pin-pointed 

 this basic cause: it appears to be cold injury. 



This cold injury usually occurs in early soring v,;hen the trees have 

 become physiologically active, not during the winter when the trees are 

 in their rest period. And it does not have to get very cold to produce 

 injury, in 194-9, a low temperature of 26°F. killed thousands of trees. 

 The injury occurs primarily in the cambium and phloem tissues, and appears 

 as a discoloration in the cambium extending from the ground level upward 

 to 2-3 inches above the crotch along the scaffold limbs. After a few 

 warm days, a characteristic *'sour sap" odor resulting from fermentation 

 of the injured tissues occurs. 



Results of studies by Dr. Savage's group at Experiment, Georgia, 

 are rather startling. They have found that tree trunk temperature is 

 much higher in winter than in summer. This happens because in the winter 

 solar radiation penetrates directly into the bark, and is absorbed by the 

 dark-colored bark. Such large amounts of heat are accumulated that trunk 

 temperature may rise M-0°F. or more above air temperature. This situation 

 does not occur in the summer because (1) the trunk is shaded by leaves 

 and (2) cool water is being drawn through the trunk, from the soil to the 

 leaves . 



Of course, these high trunk temperatures persist only during daylight 

 hours. At night, trunk temperatures fall to near air temperature. Thus, 

 if a bright, sunny day is followed by a cold night, violent fluctuations 

 of trunk temperature can occur. For example. Savage described a sunny, 



66°F. day followed by a M- F. night in 1963 the tree trunks were exposed 



to about a 100 F. temperature drop in 10 hours. If the tissues are dor- 

 mant, they may survive such a shock, but if they are physiologically ac- 

 tive, severe injury and subsequent death of the tree can be expected. 



An important factor in this situation is trunk size. The larger 

 the trunk, the more heat will be absorbed and retained during solar ir- 

 radiation. Seldom does injury occur to less-than-4-year-old trees, sim- 

 ly because they do not absorb as much heat and therefore experience such 

 violent temperature fluctuations- This is also why most of the injury 

 occurs in the trunk rather than in scaffold branches. 



