Dr. Grow: Sunscald is a common problem for newly planted trees

I have received two phone calls in the last month asking about damage to bark on trees planted within the last two years. Both situations have similar characteristics, so I thought this might be a problem common to a lot of newly planted trees in the area.

After inspecting the trees I noticed some similarities. First, the damage to the bark was on the west and southwest side of the trunk. Second, the bark of the young trees was thin. In one case, the trees were varieties of maple, while in the other, both maple and ash were found to be damaged.

The damage was evident up and down the tree in a band about two inches wide. If a limb was just above a damaged area, the limb usually died over the summer.

After looking at the damage and recollecting weather conditions over the last two years, I came to the conclusion that these trees were suffering from sunscald. A few different scenarios can result in the physical damage.

In the first scenario, trees grown in a nursery are often placed close to each other. Each tree shades its neighbor. When these trees are planted in a landscape, they often are planted in full sun. The bark is not used to having direct sun shining on it, and it gets sunburned. The sunburn causes sunscald.

Sunscald also develops during the winter when warm winter days alternate between cold winter nights. Cambia cells (the layer between bark and wood) will develop resistance to cold during the winter. During normal cold days and nights, no physiological changes occur. But when the warm, west afternoon sun shines on thin-barked young trees, these cells temporarily lose their resistance to cold and often freeze. These frozen cells erupt from the ice formed and die. The result is a dead longitudinal strip developing on the west side of the tree trunk.

This problem can develop just as it did in spring 2007. We had a warm March. Trees and shrubs came out of dormancy early that year. Then in early April we got temperatures well below freezing. Again, the bark on the western side of the young stems warmed up during the day and refroze during the night. The result was a longitudinal strip of frozen, dead cambial cells on the west side of these young trees.

If you have this same kind of problem in young trees in your landscape, there are a couple of things you can do to help them overcome this dead bark problem. First, using a small knife, cut the loose bark back to where the bark is firmly attached to tree wood.

Next, spray pruning sealer over the damaged area every two to three months during the growing season, until the damaged area has been covered by new bark. This may take two to four years. The living bark on either side of the damaged area will slowly converge until the damaged area has been covered.

In order to prevent the damage from occurring in the first place, cover thin bark, newly planted trees for the first two or three winters with either paper or material tree wrap. Place the wrap on the tree trunk in November or December and then remove it in late April. If you leave the wrap on the tree during the summer months, the wrap will act as a hiding place for insects.

Sunscald is a common problem for newly planted trees in the area. With a little preventive maintenance (wrapping your new trees' stem with tree wrap during the winter) you can eliminate this problem. If sunscald is evident in some of your trees, you can prevent further damage by spraying the damaged area with pruning paint until the bark has repaired itself over two to four years.

Send your gardening and landscape questions to Paul Schnare at P.O. Box 699, Cape Girardeau, Mo. 63702-0699 or by e-mail to news@semissourian.com.