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FACTORS CONTRIBUTING TO LOW TEMPERATURE INJURY 



IN STRAWBERRIES 



Bertie R. Boyce 

 Department of Plant and Soil Science 

 Vermont Agricultural Experiment Station 

 University of Vermont 



Winter injury occurring in strawberry plants can be a serious 

 problem in northern regions. The degree of injury may range from 

 none, to that severe enough so the plants do not survive. Inter- 

 nal crown discoloration is often used in the field as an indication 

 of the degree of injury: the darker the crown tissue, the more se- 

 vere the injury. Our experiments have indicated that enough injury 

 can occur to reduce yields without discoloring the crown tissue. 

 Moderate injury can go undetected and yet reduce berry size or num- 

 ber and thus total yield. This may be the cause of relatively low 

 yields that cannot be attributed to other factors. 



How much injury occurs and how vigorous the plants will be 

 the following spring, depend upon many factors. These factors can 

 be divided into three groups: (1) conditions that determine how 

 much resistance to low temperature injury the crowns will attain; 

 (2) conditions that bring about injury; and (3) conditions to which 

 the plants are subjected following injury. Most of the strawberry 

 hardiness research at Vermont has dealt with the first two groups. 



How much resistance to low temperatures will be attained dif- 

 fers with varieties. We have screened many varieties under arti- 

 ficial freezing conditions and found a wide range among them. Cat- 

 skill and Sparkle were among the hardier varieties tested, while 

 Earlidawn was among the least hardy. Nutrition, soil moisture, and 

 fall temperatures all play a role in determining how hardy the 

 plants will become. If mulched too early, the degree of hardiness 

 attained will be substantially less. Periodic sampling and arti- 

 ficial freezing indicate that maximum hardiness is not reached un- 

 til mid-November in the Burlington area. 



A strawberry plant, after reaching its maximum hardiness, is 

 still not a hardy plant. Tissue temperatures low enough to kill 

 strawberry plants would not injure peach buds. If the crown tem- 

 peratures approach 20 F, injury will probably be severe enough to 

 reduce yields. If the crown temperatures reach 10 F, the plants 

 are unlikely to survive. 



In controlled freezing tests, rapid freezing and thawing in- 

 creased crown injury. This probably is not a factor under field 

 Conditions because close proximity to the soil and a covering of 

 mulch usually prevent rapid freezing or thawing. 



The amount of injury increases as the time the tissue remains 

 frozen increases. This could be significant at temperatures above 

 that where the plant is killed, but within the temperature range 



