We cut all of it off and burned it. Please advise us what treatment we should use. Some crape myrtles are highly susceptible to powdery mildew, and some years are better than others. This has been a great year for powdery mildew. If the entire plant is covered in it, sprays are suggested.
Heavy infestations can cut down on photosynthesis, which in turn can hurt blooming.
If there is only a light coverage, ignore it. Spray with Daconil, Funginex or similar general fungicide. I trim them every year, but I notice around town that some people have already trimmed them back for this year and I generally wait until close to springtime. Many people begin pruning their crape myrtles as soon as they lose their leaves in the fall. While this can be done, I too, prefer to wait until late February.