Wednesday, January 7, 2009 3:06 PM CST

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 Michele Warmund. 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,” she said.

Insects like the flatheaded appletree borer can gain access to the trunk, worsening the 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 such as waterproof kraft paper, tree wrap or vinyl tree guards. Vinyl guards are more expensive but can be reused  for several years.

As a rule, you should apply wraps and guards by December, but it’s still not too late, she said.

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.

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