By Morgan Pickett
University of Minnesota
Extension
As we head into the winter months, and before we snuggle in for the winter. Let’s take one last look at our young trees and wrap them up, too.
Sunscald, also known as sunburn or frost canker, is a condition that primarily affects the bark of trees, especially young or thin-barked trees, often seen particularly in winter or early spring. Thin-barked trees are more susceptible to various environmental factors, including sunscald. Thin-barked trees include: maple, birch, dogwood, linden, and willow trees. Sunscald occurs when there is a sudden increase in temperature, causing the tissue in the bark to warm and become active and out of winter dormancy. When the sun sets or clouds block the sun, and the temperature drops rapidly, it can lead to damage in the active cells. This damage can result in sunken, discolored, or cracked areas on the bark.
To prevent sunscald in trees, especially newly planted or young trees, consider the following measures:
Wrap the trunk: Use a white commercial tree wrap or plastic tree guards. Do not use brown or black wrap or guards, as they will absorb heat from the sun. Placing black tree wrap will increase the temperatures which will cause more dormant tissue to become active again. Wrap a newly planted tree for at least two winters and thin-barked species up to five winters. Be sure to remove all tree wraps in the spring.
Provide shade: If possible, provide temporary shade for young trees during periods of intense sunlight. This can be achieved with shade cloth or by raising temporary shade structures.
Mulch: Apply a layer of mulch around the base of the tree to insulate the soil and regulate temperature. This helps maintain a more stable environment for the tree’s roots and trunk. Do not mound up the mulch around the trunk, as this will cause other issues.
Proper watering: Ensure that trees are adequately watered, especially during dry periods. Well-hydrated trees are more resilient to temperature fluctuations. When watering newly planted trees, apply 1-1.5 gallons per inch of the diameter of the trunk each time you water. It’s recommended that you continue to water your trees until the ground is frozen and begin watering again when the ground thaws in the springtime.
Avoid pruning in late fall: Late fall pruning can leave fresh cuts on the tree, making it more susceptible to sunscald. Consider delaying pruning until late winter or early spring
By taking these preventative measures, you can help young trees thrive and reduce the risk of future related disease issues. If you have questions about this or any other agriculture, horticulture or natural resource topics please reach out to your local Extension educator. Residents in Fillmore and Houston counties call (507) 765-3896 or (507) 725-5807.
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