You may have seen this powdery-white substance on the leaves of your crape myrtles. Powdery mildew is one of the most common problems of crape myrtles.
Does it harm the tree? While powdery mildew is not typically fatal to trees, it can cause noticeable damage if left untreated. It is a type of fungus that thrives in warm, humid weather. Our Texas gulf coast is the perfect breeding ground. Powdery mildew typically appears as white or grayish spots on the leaves.
Aphids feed on tender new leaves from which they suck plant sap. Plant sap has a high sugar content. When they feed, the aphids excrete large amounts of sugary liquid called honeydew. The honeydew serves as food for the sooty mold fungi. The result is the unsightly white or grayish fungus that grows on the leaves.
Aphids and Powdery Mildew
What can you do about the aphids and mildew?
If aphids are still present, an insecticide will take care of the source problem. The fungus will stay on the leaves until they fall off the tree. Some of the fungus can be knocked off with using a heavy stream of water. The fungus won't hurt the tree.... just very unsightly.