Other factors affect the acclimation process, so that resis- 

 tance to very low temperatures does not always result from exposure 

 to below freezing temperature. It is pretty well established that 

 conditions which favor accumulation of carbohydrates in the bark 

 and woody tissue also favor acclimation to low temperature. Maxi- 

 mum accumulation of carbohydrates depends on active photosynthetic 

 activity in the whole tree for the whole growing season. Foliage 

 diaease or injury, inadequate water or nutrition, shading, severe 

 hail damage, or a growing season shortened by early frost will 

 obviously limit photosynthetic production of carbohydrates. It is 

 also recognized that a heavy fruit crop will draw off carbohydrates 

 that would otherwise be available for storage in the tree tissues. 

 There is some evidence also that chemicals produced by the crop 

 seeds may directly inhibit cold acclimation. 



Reports of cold hardiness studies indicate that we cannot assign 

 any specific safe temperature minimum to a tree at any given time. 

 Duration of exposure to the temperature minimum must be considered. 

 Injury increases with the length of exposure to cold as the lethal 

 temperature is approached. Also, repeated freezing and thawing has 

 an amplifying effect on injury, 



A given level of cold hardiness is subject to change toward 

 less hardiness if the day or nighttime temperature gets much above 

 freezing. Just how much hardiness is lost undoubtedly depends on 

 length of exposure and how high the temperature goes, but these 

 relationships have not been clarified. In peaches it appears that 

 deacclimation (loss of the acclimated condition) is minimal during 

 the rest period, but can take place very rapidly on exposure to a 

 few hours of warm temperature any time after the rest period is 

 completed. The rest period is usually completed in late January or 

 early February in New England peaches. 



Pruning in the fall or early winter makes trees more suscepti- 

 ble to cold injury. Again, an acceptable explanation of why this is 

 so has not appeared. Early pruning was obviously a major contribut- 

 ing factor to the trunk injury in some orchards in the 1975-76 

 winter. At Storrs, the only trees to show trunk damage were those 

 (18-year-old Jerseyred) that had been heavily pruned in late Novem- 

 ber and early December. No further pruning was done until early 

 February. Comparable Jerseyred trees pruned similarly in February 

 showed no damage. Injured trees lost 50-901 of the bark around the 

 trunk in the spring of 19 76, These observations indicate the damage 

 must have occurred during December or January. December temperature 

 went to zero or lower on two days; Christmas Eve (0°F) and Christmas M 

 Day (-1°F) at Storrs. In January, 4 subzero readings were recorded: 

 -1° the 18th, -3° the 19th, -8° the 23rd, and -5° the 24th, In 

 February the lowest minimum was +5° on the 3rd. 



The fall of 1975 was unusual in that it remained quite warm 

 through the middle of December. The lowest for November was 27° 

 and daytime highs were over 60° as late as the 21st and 22nd. 

 December continued the warm trend with 61° Dec. 1st, and 60° the 



