Question: What is the white powdery substance on my Crape Myrtle?

Answer: Crape myrtles are popular landscape trees in the South known for their summer flowers and attractive bark. Crape myrtles are known for being essentially trouble-free plants with little disease and few insect problems. One problem that is often seen on crape myrtles is a disease called powdery mildew.

Powdery mildew is a disease that is common on many ornamental trees and shrubs, including crape myrtles. Powdery mildew is a powdery white to light gray-colored fungus that will grow on succulent stems, leaves, buds, and flowers. Young plants and new growth are usually more severely damaged than older plants, leaves, or branches. Flowers that are heavily infected may fail to open. Parts of the plant that are severely infected will usually look distorted and stunted.

Powdery mildew usually occurs in the spring, fall, and winter months during cool weather. Powdery mildew will also show up in shady, damp locations especially where plants are crowded and air circulation is poor. High humidity and rainy conditions are good environmental conditions for powdery mildew to occur.

The good news is that there are several control measures that can be followed in order to prevent and treat powdery mildew. If you are getting ready to purchase a crape myrtle, you can immediately control powdery mildew by purchasing a resistant variety and avoiding susceptible varieties. The level of resistance to powdery mildew varies for particular crape myrtles. Location and environmental conditions can also affect the level of resistance in some crape myrtle varieties. Some crape myrtle varieties will have good to excellent resistance to powdery mildew, while others will be very susceptible. When shopping for crape myrtles note the variety and check for the extent of resistance.

There are some cultural practices that will help reduce or prevent powdery mildew from occurring on crape myrtles. Be sure to remove sprouts (suckers) at the base of the plant as they occur. Since the sprouts are new growth, they are more susceptible to powdery mildew. Once these sprouts become infected, the fungus easily spreads to the upper portions of the plant.

Planting crape myrtles in the proper location will also help discourage powdery mildew. Crape myrtles should be planted in a sunny location. Planting a crape myrtle in a shady location will not only encourage powdery mildew but shade will also reduce flowering.

When pruning your crape myrtles, be sure to thin branches so that you are allowing for good air circulation throughout the tree. Good air circulation will allow the leaf surface to dry out more quickly after a rain and will reduce wet surfaces for powdery mildew to show up on. Pruning out severely diseased portions of the plant will also help reduce the disease if only a few parts are infected.

If the disease is severe enough, there are some chemical control options available. Examples of active ingredients of fungicides used to control powdery mildew on crape myrtles and many other ornamentals include: myclobutanil, propiconazole, and triadimefon. When using fungicides remember to read the label and follow directions.

Powdery mildew is a fairly easy disease to manage, or avoid, on crape myrtles. By following some of the practices mentioned above, you can enjoy the beauty of the crape myrtle throughout the summer instead of worrying about powdery mildew.

Reminder: A growing program this year is the “Sampson County Friends of Horticulture.” This program offers monthly “How To” Horticultural Seminars. Please call (910) 592-7161 for more information. Please call the Sampson County Cooperative Extension Center at (910) 592-7161 with your horticultural questions and to register for any upcoming events. Be sure to check out the Ask An Expert Widget at sampson.ces.ncsu.edu for any questions you may have.