By JASON GRAVES
K-State Research and Extension Central District Horticulturist
Winter injury has been a common problem on young and even mature trees here in central Kansas over the last several seasons. Winter tree injuries are frustrating because the damage may not be seen or noticed until much later the following year.
Winter injury can come in the form of sunscald/freeze injury or winter desiccation (drying) damage. New and young trees and evergreens are the most susceptible to winter injuries. Proactive measures can help reduce this type of damage in 2024-25.
Sunscald
Sunscald is a term for the cracking and splitting of tree bark caused by rapid heating or cooling. It can occur both in the extreme heat of summer and during the winter.
A typical winter day in Kansas may be sunny and 40-50 degrees. High-intensity sunlight occurs at lower angles during the winter, heating the south and southwest sides of tree trunks. The heat can cause cells to come out of dormancy and become active.
Once the sun sets or the weather quickly turns below freezing the active cells and conductive tissue are killed.
Symptoms of sunscald initially appear as sunken and discolored bark, which later cracks, splits, and falls off the tree in patches. Thin-barked trees are especially prone to sunscald. Maples, fruit trees, willows, lindens, honey locusts, some oaks and many other trees can easily be damaged, especially when young.
What to do
New and young trees can be wrapped to minimize winter sunscald. Commercial wraps, such as corrugated plastic guards or crepe paper, are easy to use. Plastic guards slip around the trunk, while crepe paper-style wraps should be applied upward from the base to just above the lowest branches, overlapping about one-third with each turn.
Wrap trees from November to April (Thanksgiving to Easter) to help shield trunks from sunlight and heat. Paper-type wraps should be removed in spring to avoid pests that may get underneath. Repeat this process each winter until the bark thickens and becomes corky. Wraps also help protect against feeding damage from rabbits and rodents, which can harm young trunks during winter.
Winter desiccation
Desiccation means drying out. A dry winter is stressful on any tree, especially on evergreens. All plants continue to transpire during the winter, and freezing plant tissue or frozen soil may restrict water conduction. When water loss through transpiration isn’t replaced, winter drying kills portions of the plant. Winter desiccation is worse on the side of the plant facing the wind.
Freeze injury can occur even when soil moisture is adequate and is usually the result of extreme temperature swings during mid-winter. In Kansas, warm January days can cause trees to lose their acclimatization to cold, making them more vulnerable if freezing temperatures return suddenly.
What to do
Prevent desiccation by ensuring that trees and woody plants have access to moisture throughout the winter. Recent rain has helped provide some soil moisture, but this needs to be monitored throughout the winter, especially on young trees and evergreens.
If conditions become dry, a mid-winter watering will be of great benefit. Trees and shrubs can be watered when needed during the winter on days when the temperature is at least 40 degrees, and the soil isn’t frozen.