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Why is my Crape Myrtle Covered in Powder?

Branch on a table with white coating

It’s a common question asked by gardeners and property owners – why are my Crape Myrtles covered in a white powder? The answer is: Powdery Mildew, or Erysiphe lagerstroemia.

Powdery Mildew is usually a problem in the spring where nights are cool and days are warm. Long periods of dry weather call also accelerate powdery mildew’s growth. Young and soft areas of the plant are more likely to be affected by the disease rather than the more mature and hardened tissues.

It can be identified by small white areas on younger leaves at first. Once the disease is well-established, it can also be associated with a rusty discoloration and a thick white coating. The long term effects of powdery mildew can include stunting the growth of young leaves, shortening stems on foliage, buds that never bloom and in the end defoliation.

Like most ailments, prevention is the best way to avoid these long-term problems. You can achieve this by growing fungal-resistant Crape Myrtles cultivars. Some examples are: Apalachee, Biloxi, Cherokee, Choctaw, Commanche, Hope, Muskogee, Pecos, Seminole, Sioux, and Yuma. These work best in the east and southeast. They may have trouble thriving in the pacific northwest.

Additional ways of preventing powdery mildew is to plant the trees with enough space and distance to allow ample airflow and sunlight to reach the entire plant. The spores of Erysiphe lagerstroemia cannot survive a dry heat. Though it seems counterintuitive, the spores also do not thrive in an excess of water, so a heavy rain will not necessarily increase or worsen a case of powdery mildew. But a quick drying process, with warm sunlight and a breeze, can eliminate the threat altogether.

How do I remove powder from Crape Myrtles?

To treat an existing case of powdery mildew, horticultural oils such as neem oil, mint oil, rosemary oil, and jojoba oil can be quite effective. To apply, coat the plant in a generous amount of the plant-based oil spray (2.5 teaspoons per gallon of water) as soon as you have discovered the presence of the disease. Repeat every week, and by doing so, you can help eradicate even a moderate outbreak.

There are also store-bought chemical remedies for treating Erysiphe lagerstroemia which include ingredients like potassium bicarbonate, sulfur, and copper. These can be wildly effective, but overuse can also cause phytotoxicity and damage the plants. Following labeled directions and practicing safe application will work best for your plants and for you.

While powdery mildew is a non-fatal annoyance to your Crape Myrtles, you don’t have to endure it for much longer. Follow these recommended steps for prevention and treatment, and your trees should be back in perfect health in no time, or contact Sussex Tree today!