Protect Young Trees

By John Wilson

Extension Educator

Recently I’ve talked about injury we might see on evergreens or turf with our open, dry winter. Today I wanted to visit about another kind of injury that often occurs on trees during the winter, but it doesn’t matter on this one whether we have lots or little snow.

While evergreen trees and shrubs are susceptible to winter desiccation or drying, sunscald is a winter injury that can occur on southwest side of deciduous or broadleaf trees. Sunscald occurs when tree bark warms up on sunny days and dormant cells become active. Once active, plant cells lose some of their cold hardiness and are then injured when temperatures drop at night.

Sunscald damage appears as discolored bark, cracking, or sunken areas. This damage stresses trees and provides an avenue for insects and diseases to enter. Often the injury may take place under the bark, but it doesn’t become evident for a year or more.

Sunscald is mainly a threat to young, thin-barked trees with southwest exposure. As most young trees mature, they develop thicker bark and become less susceptible to sunscald injury. However, trees that have thin, dark-colored bark, such as cherries, peaches, and plums, even as they mature can remain susceptible even with age.

Drought stressed trees are more susceptible to sunscald than trees that go into winter well-hydrated. This is another reason to pay attention to correct fall watering; especially of young trees. Deep watering and using mulch to conserve soil moisture are good practices.

Avoid over pruning young trees, especially removing lower limbs earlier than needed. Lower limbs provide some shade to tree trunks during winter. Wait two to three years after planting before removing the lowest tree limbs. If possible, plant susceptible trees to the north and east of buildings or of evergreens. This way, the lower portions of the trees will be shaded during winter.

Protecting trees from sunscald is fairly easy and inexpensive. Wrapping the lower branches and trunk of susceptible trees with light colored tree wrap during winter is the best prevention. Tree wraps can be purchased at most home and garden stores.

White or light colored tree wrap reflects light helping to keep tree bark cooler. Dormant cells then remain inactive and are at less risk of being injured by temperatures dropping at night or suddenly when a cold front or cloud cover comes through.

Ideally, wraps should be put in place in late fall. If you have a susceptible tree, there is still time to protect it. As air temperatures warm in mid- to late winter, the risk of sunscald increases. Warm winter days followed by cold nights can be more common in late winter.

All tree wraps need to be removed in spring after the risk of freezing has passed. Tree wrap left on a tree during the growing season can harbor pests and hold moisture against a tree trunk which may promote disease.

Sometimes people with orchards paint the trunks of fruit trees white during winter. This is usually not acceptable in a landscape, but if trunk painting is done use an interior latex paint. Some exterior paints contain antimicrobial agents that could damage a tree.

If sunscald injury does occur, the area may repair itself. In the meantime, damaged areas should not be painted with a wound dressing or filled with any sealing substance such as paint or tar. These products can interfere with the trees own natural process to close the wound.

For more information on protecting trees from sunscald, contact your local UNL Extension office.