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Winter injury

Very few raspberry varieties are completely hardy in Minnesota; even hardy varieties can exhibit symptoms of winter injury following severe winters. Winter injury can also occur after winters when the temperature fluctuates between mild and extremely cold.

winter-injury

Winter injury on 'Nova' raspberries.

Thaddeus McCamant, Central Lakes College

Winter injury is often confused with cane blight, but it can be distinguished from biotic diseases due to its characteristic symptoms. The tips of the canes are most susceptible to winter cold. Mild winter injury will result in the death of the top few inches of a cane. With severe winter injury, the top few feet of the canes will die. In almost all cases of winter injury, there will be healthy leaves at the bottom of the cane. If the winter injury occurred with a few inches of snow, then the canes die to snow level and will produce healthy leaves and fruit from the lower canes.

Raspberries that produce flowers and fruit on first year canes (primocanes) will always show some dieback in the spring. Dieback in fall-bearing raspberries is normal and is not considered winter injury. Flowering in primocanes always starts at the tips of the canes and later flowers sprout lower in the cane. Any part of the cane that produces flowers will die in the winter. The summer-bearing variety Nova produces flowers on the top six inches of the primocane each fall, so dieback is minor. Fall varieties like Autumn Britten, Heritage and Caroline often produce flowers and fruit on the top 3/4 of each cane, and only 1/4 of the cane will survive each winter.

Always choose varieties that are suitable for your zone in Minnesota. Nova, Killarney and Boyne red raspberries are all rated for zone 3. Royalty purple is rated for zone 4, but will often survive colder winters, if the canes are healthy. The canes of some fall-bearing raspberries, such as Autumn Bliss, are killed even during mild Minnesota winters. Those varieties can successfully be grown here, because the new canes sprout and bear fruit each year, and the dead canes are removed each spring.

Winter injury can also be aggravated by biotic diseases. Leaf spot, spur blight, cane blight and anthracnose can make raspberries more susceptible to winter injury. Healthy plants will survive the Minnesota winters better.


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