Small Fruit Winter Injury Update
Strawberries
The duration of cold temperatures, the amount of snow cover you may have had at the time, and the amount of straw mulch applied are all factors that can influence the amount of damage caused. This can range from mild injury, causing reduction in vigor, all the way to extensive damage that is of major concern.
To assess your damage, take the following steps:
- Go out now and sample your field; take plants from across the bed, outside edges to the center.
- Cut open the strawberry crown from top to bottom (vertically), rather than crosswise (horizontally) to determine the extent of damage.
- Immediately evaluate the color of the crown – with no winter injury the crown should have a creamy-white color.
Injury levels
Mild injury would result in a brown flecking inside the cut crown. The deeper the brown coloration in the crown, the more damage is indicated. Plants will grow out of this medium damaged condition and can produce a normal crop.
Major or extensive damage would result in the crown having a dark brown color and corky texture.This condition is the most concerning and requires careful spring management of the field.
Damage needs to be managed carefully to harvest the best crop; this includes:
- Minimizing stress to the plant. The efficiency of the plant to make use of water and nutrients may be reduced because the conduction tissues have been impacted.
- Maintaining good moisture levels. 1 –2 inches per week, through the harvest period, which allows the damaged tissue to absorb the required moisture.Managing fertilizer applications. Light nutrient applications, either ground applications of granular nitrogen or foliar applications with spring fungicides. Depending on the degree of damage, a range of 15 –30 pounds of actual nitrogen per acre would be effective by “spoon feeding” small amounts over several applications.
Closely monitoring moisture levels and nutrient applications through the harvest period is critical to maximize your yield from these stressed plants.
Brambles
With raspberries and blackberries, winter injury can appear in a variety of ways. Very cold temperatures during the winter can kill overwintering floricanes and damage the crown and root system in extreme cases. Late frost in spring can result in injury or even death of flower buds on floricane-fruiting varieties, drastically impacting yield. The most typical form of winter injury, however, results from fluctuating temperatures during the dormant season. This injury occurs after plants have achieved their chilling requirements and are no longer fully dormant. Variable temperatures during the winter tend to damage less coldtolerant tissue. March can often be when injury occurs as you see more fluctuating temperatures, rather than in mid-winter when plants are totally dormant.
Winter injury typically kills or damages the overwintering floricanes but not new primocanes. There are a variety of methods for assessing winter injury that allow you to evaluate the extent prior to spring pruning. One of the simplest methods includes cutting buds lengthwise (tip to base), as buds have begun to swell to check for blackened centers or damaged tissue. This assessment can also be done prior to bud swell by putting cut canes in a bucket of water in a warm sunny location.
Winter injury is prevented by making appropriate site selection, avoiding frost pockets, having good air drainage, and planting sufficiently winter hard varieties for your area.
