white powder on crape myrtle
Your crape myrtle and Japanese maple are suffering from powdery mildew. We have seen increasing incidences of his malady on both of these plants during the past couple of summers, due primarily to the cool, wet conditions experienced during the spring and early summer weeks.
This fungal disease rarely kills mature plants, but it will weaken them somewhat. Fungal diseases cannot be cured once the symptoms appear, but they can be prevented or slowed by spraying the plant with a fungicide before the symptoms appear or immediately after the first symptoms appear.