Tales From the Help Desk: Crape Myrtle Bark

Q.  My crape myrtles have splits on the bark.  What is going on?

A.  Your crape myrtles appear to have sun scald.  Crape myrtles, Lagerstroemia indica, are considered a relatively problem-free tree. The Clemson Cooperative Extension website cites the most common problems as powdery mildew, Cercospora leaf spot, aphids, Japanese beetles, sooty mold, and the recently recognized crape myrtle bark scale. Clearly, the photo of your tree shows no indications of any of these diseases and insects. Your tree likely has sunscald. While sunscald typically occurs in trees with thin bark; crape myrtle is not one of the most common types of trees where sunscald is frequently observed. However, it can occur in crape myrtles. Tree Call had a client a few years ago whose crape myrtle had sunscald.

Sunscald can occur from either winter or summer sun. A common cause of sunscald is light reflected off snow, but it can be caused by direct sunlight. Per University of Connecticut Home and Garden Education Center Fact Sheet, sunscald can also occur “when a tree’s canopy has been overly pruned or another shade-providing tree or man-made structure has been removed.” Symptoms do not show up until later, such as the following summer.

Trees go dormant in winter, but growth can be reactivated by warm weather or the warmth of the sun reflected off the snow. Once active, the cells are not able to return to dormancy by nightfall. At night, temperature falls to levels that kill the active cells. This damages the outer layer of the tree’s trunk and causes lesions or damaged spots which then provide an opportunity for microorganisms such as fungi and bacteria, or insects, to enter the tree.  Sunscald occurring in summer is caused by excessive heat reaching a particular area of the tree and killing the cells. Sunscald most frequently occurs on the southwest side of the tree’s trunk.

 

This article first appeared in the April 2022 edition of The Colonial Master Gardener.