By pruning in December, and that severely, it could make the plants more susceptible to winter damage, should cold weather occur. Try to encourage the caretaker of these plants to allow them to grow, and limit pruning to thinning cuts and shaping. All of the upper branches are covered with a mold like growth. 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.