I had a problem with black leaves on my crapemyrtle last year. How do I prevent that this year? JW

First of all, congratulations on having a crapemyrtle that survived the deep freeze last year. As we all know, many of our crapemyrtles did not do well. But, for those that did make it, black leaves are an indicator of crapemyrtle bark scale (CMBS).

Adult male CMBS insects have wings they use to help find females for mating. Mated females then produce egg capsules, lay between 60-250 eggs in these capsules and then die. In addition to the black leaves you mentioned, these white puffy egg sacks are another indicator of CMBS.

The eggs overwinter in these pouches and begin to hatch in April and May. The tiny insects that emerge are very small and pink in color. They move about by hitching rides on birds or being blown by the wind to nearby plants. A second generation emerges in late summer.

These scale insects have what we call piercing/sucking mouth parts. Using these mouth parts, they are able to pierce the bark and suck nutrients out of the plant. With small infestations, the crapemyrtles are not in danger. But over time, as their population increases, they can build up to the point of being able to damage the plant.

The black leaves you mentioned are another primary symptom of CMBS. The leaves themselves do not turn black but instead are covered with a black fungus called sooty mold. The mold is caused by the excretions of the scale insect we affectionately call “honeydew.” An increased presence of ants on your crapemyrtle is also another indicator of CMBS since ants apparently love to eat this sweet honeydew. In small amounts, these blackened leaves are not going to cause a problem (other than aesthetic) but if allowed to spread throughout the plant, the crapemyrtle won’t be able to survive.

There are various strategies to deal with CMBS during the growing season, but the absolute best way to deal with them long term is in the winter on days when the temperature is over 50 degrees. Since the crapemyrtle is dormant during the winter, you can spray them with what is called a dormant oil. Dormant oil is a thicker consistency oil than regular horticultural oil and would not be safe to use on your plants during the growing season. But is great to use during the winter on scale insects. Because of its thicker consistency, it does a better job of smothering the scale insects in their protective enclosures. Dormant oil is available at your favorite garden center. Just mix with water in a pump garden sprayer according to directions and give your crapemyrtle a good soaking. Doing this will really put a dent in your CMBS population. Good luck!

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org.

Photo Courtesy: Helene Doughty, Virginia Polytechnic Institute and State University, Bugwood.org