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Wraps or guards can lessen winter damage to young trees

Published: October 06, 2009

Story Source: Christopher Starbuck, 573-882-9630

COLUMBIA, Mo. - Tree wraps or guards can lessen the risk of southwest injury, a condition that can afflict young trees in winter, said a University of Missouri horticulturist.

Southwest injury, or trunk scald, occurs on the lower portion of the trunk, said Chris Starbuck. Low-angle winter sunlight warms trunk tissue during the day. This warming can activate dormant cells that become vulnerable to injury as temperatures plunge in the evening.

"Trunk cracking or splitting on the south or southwest side of the tree are common symptoms, as well as sunken areas in the bark," he said.

Insects like the flatheaded appletree borer can gain access to the trunk, worsening the injury.

Fall is a good time to wrap the trunks of recently planted trees to lessen or prevent southwest injury.

Thin-barked ornamental trees such as red maple and ornamental cherry are particularly at risk. You can protect the lower trunk by covering it with a light-colored material that will reflect sunlight, such as waterproof kraft paper, tree wrap or vinyl tree guards. Vinyl guards are more expensive but can be reused for several years.

An alternative is to apply white latex paint to the lower portion of the trunk, he said.

Never use a dark wrap, since this can actually increase trunk scald damage.

When you wrap the trunk, begin at the soil line and spiral the paper around the trunk up to the first branches, overlapping the edges of each layer.

Remove wraps and guards in early spring. Materials left on too long can restrict tree growth and provide a protected environment for insects and disease organisms. Wraps and guards also limit coverage of pest-control products.

Removing the wrap in spring promotes bark thickening during the growing season, making trees less vulnerable to trunk scald the following winter. In most cases, wrapping the trunk during the first winter after planting should be sufficient.