garden

From The Ground Up: Prevent sunscald on susceptible trees this winter

Winter weather has arrived and young trees need a little TLC to avoid a common malady called sunscald.

Sunscald is a common problem found in young thin barked trees, such as maples, beech, dogwood, honey locust and fruit trees. But what causes sunscald? What does sunscald look like? There are a couple schools of thought as to what causes sunscald. Dehydration may be a factor due to the direct sun or reflected sunlight from snow exposure, which could cause the bark tissue to die. Another theory suggests that when bark heats during the day, the tissues break dormancy, and the freezing temperatures at night kill the tissue, which creates an area of dead bark. Damage occurs in late winter or early spring. The bark may show as an elongated canker (areas of dead bark) that appears sunken or discolored, followed by cracking and peeling of the bark. You’ll find the damage on the south or southwest side of a tree.

Wrapping your tree before winter on these thin barked trees may help prevent sunscald. Damage will not show until next spring or summer when new growth appears. The tree will most likely survive, and there is nothing more to be done at this point as the tree will usually heal itself. Unfortunately, decay may follow, which is an easy entry for insects and disease, making the tree a risk to fail. Do not try to seal the open area with anything, as that may actually make it worse.

Winter weather brings other challenges to trees as well. While bark does an excellent job of protecting trees, wildlife may have other ideas. By looking at the height of bark damage, critters may be identified. Voles tend to eat bark at the base of young trees. Rabbits will feed on tender bark from young trees and bushes, especially in years of heavy snow falls, when ground cover feeding is not an option. Rabbits can girdling the tree, which means eating the bark all the way around a branch or tree. All branches above the girdling will die, unfortunately. Deer tend to strip bark, as well as damage bark by fraying their antlers to shed the velvet coating.

Be sensitive to surrounding trees when applying deicing salt to driveways or sidewalks. Many trees such as white pine and crabapple are sensitive to high salt levels in the soil, and the excess salt may stress the trees, resulting in leaf scorch or needle browning.

In conifers, brown needles found on the south side of the plant are a sign of winter desiccation. Drying winds increase the loss of moisture from the needles, and the freezing ground can’t take up any more moisture. So it’s best to continue to water conifers weekly until the ground is frozen.

For questions, call the Linn County Extension Master Gardener Hotline at (319) 447-0647.

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