image of sun scald presenting on bark of ash treeYoung trees, newly planted trees, and thin-barked trees are most susceptible to a process called sun scald, or southwest injury. On a sunny winter day, the bark temperature of your tree can increase 20 degrees higher than the air temperature.

This can cause tree cells to come out of dormancy and become active. When the sun is blocked, shadows cause the bark temperature to drop rapidly or a warm day gives way to near zero temperatures at night. This temperature drop kills these active cells and conducive tissue before it can return to the protection of dormancy.

Once sun scald occurs, cracked areas at the bark level or beneath begin to form which dries out the tree causing leaves or pine needles to appear brown or discolored and bark to die and fall off. Trees that have been pruned to raise the lower branches, or moved from a shady to a sunny location are also sensitive. This condition can kill a tree or make it vulnerable to toppling by snow.

Sun scald can be prevented by wrapping the trunk with a commercial tree wrap. Light-colored wraps work best as darker colors may absorb too much heat. The wrap will reflect the sun and keep the bark at a more constant temperature.

Wrap the trunk from the ground up in an overlapping swirling fashion up to the first branch.  Make sure to take it off in early spring or mold and other pests can infect the tree.  That said, don’t remove it too early; wait until after the last frost.

Newly planted trees should be wrapped for at least two winters and thin-barked species up to five years or more until they are established. To repair sun scald damage, cut the dead bark back to live layers. Wrap the trunk in subsequent winters to prevent further damage.