Growers in the Coastal Plain area of Georgia have always been 

 plagued by the very short life of their peach orchards the aver- 

 age life of trees there is only 8 years. Many years of investiga- 

 tions 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 injury usually occurs in early spring when 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 1949, a low temperature of 26° F. killed 

 thousands of trees. The injury occurs primarily in the cambium 

 (dividing) and phloem (food-conducting) 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 the 

 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 higher in winter than in summer. This happens because 

 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 40°F. or more above 

 ai r temperature . This situation does not occur in the summer be- 

 cause rn the trunk is shaded by leaves and (2) cool water is be- 

 ing drawn through the trunk, from the soil to the leaves. 



1 n 



Of course, these high trunk temperatures persist only during 

 daylight hours. At night, trunk temperatures fall to near air tem- 

 perature. 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 4°F. night in 

 1963--the tree trunks were exposed to about 100°F. temperature drop 

 in 10 hours. If the tissues are dormant, they may survive such a 

 shock, but if they are physiologically active, severe injury and 

 subsequent death of the tree can be expected. 



An important factor in this situation is trunk size. The lar- 

 ger the trunk, the more heat will be absorbed and retained during 

 solar irradiation. Seldom does injury occur to 1 ess-than-4-year- 

 old trees, simply because they do not absorb as much heat and 

 therefore experience such violent temperature fluctuations. This also 

 is why most of the injury occurs in the trunk rather than in scaf- 

 f ol d branches . 



Another important factor is wind. On a bright, sunny day, heat 

 will not accumulate in the trunk if a mild breeze is blowing, so 

 wind can be a protective influence. But at night, a wind will sig- 

 nificantly lower the temperature of the trunk on the windward side, 

 and therefore may be a damaging influence. 



