Wrap smooth-barked and young trees in the fall to minimize damage from sun scald. Sun scald can occur on sunny, cold winter days. The sun warms the tree on the south and southwest sides, causing sap to thaw. When the sun sets or goes behind a cloud or building, the temperature of the bark drops very quickly, causing the sap to refreeze rapidly, which damages the tissue in the area that had warmed up. The bark in this area will eventually slough off, leaving a scar or canker.
Cracks from sun scald can allow insects, fungus, virus, or other damage to gain an entry and begin the process of weakening the tree. As it will take many years to heal a crack, prevention is important.
Paper tree wrap or plastic tree guards will minimize sun scald. In late fall, wrap the material around the trunk, starting at the bottom, and fasten securely below the first set of branches. Remove the wrap in the spring, after the last frost. Wrap newly-planted or young trees each fall for two-to-five years, depending on the texture of the bark. Once bark is rough, the tree is mature and will no longer need to be wrapped.
To repair sun scald damage, cut the dead bark back to live tissue with a sharp knife, following the general shape of the wound; smooth off any sharp edges to facilitate healing. Wounds will heal faster when they are elliptical in shape, coming to a point at the top and bottom.
Do not use a wound dressing on the exposed area unless the wound is on an oak or elm.
Spraying with a fungicide may help prevent fungal infection.