By Judy Brisson for the Puslinch Pioneer, Feb 2022
Q: I planted three Freeman Maple (Acer rubrum) trees three years ago to shade our south facing deck. I noticed one of them had peeling bark and exposed wood this summer as seen in this photo. What is it, how do I treat it and what can I do to protect the other two trees?
A: The affected tree has sunscald and the other two are at risk. Sunscald damage occurs in the winter but is often not apparent until the next summer when new growth starts. Trees naturally go into dormancy when the temperatures drop in the fall; the tissues, including the bark tissue, stop growth. When the temperatures rise in the spring, the trees come out of dormancy and resume growth.
Sunny days in winter can warm the tree bark on the south and southwest sides of a tree enough to cause it to start to grow. When the temperature suddenly drops overnight, the tree’s inner bark cells will freeze and die. As normal growth resumes in the spring, the dead bark will appear as a sunken, cracked and peeling line on the south side of the tree. Although sunscald will not kill a tree, the damaged areas can be invaded by insects and disease. You may want to replace a young tree with extensive damage that is cosmetically unappealing.
Young trees with thin bark and some species including ash (Fraxinus), oak (Quercus), maple (Acer), birch (Betula), willow (Salix), basswood (Tilia), and honeylocust (Gleditsia) as well as most fruit trees are more susceptible to sunscald. When planting these trees on a south facing site where they will be exposed to winter sun you should protect the trunk bark until the thicker, mature bark develops. Wrap the bark with spiral white tree wrap in the fall; it will reflect the sun and keep the bark cold. Avoid wrapping trees with dark wraps or burlap which will increase the bark temperature.
Your affected tree will form callus tissue around the injury to prevent infection or further damage. You can help by trimming away any loose or peeling bark with a sterilized, sharp knife. Do not paint any substances onto the bare wood; tree paints and tars prevent healing and encourage rot and insects. Next summer keep the tree well watered. If the trees are growing in grass, remove the sod in an area 60 to 100cm around the trunk of each tree and cover with 6cm of mulch. Do not allow the mulch to touch the tree trunk.
This month temperatures will be rising and there will longer, sunnier days. To prevent future damage you should wrap all three trees now with white spiral wrap. Wraps should be removed in the spring as they can trap water and harbour insects which can cause rot and damage to the underlying bark.
Judy Brisson
Guelph Wellington Master Gardeners February 2022