I need a fact sheet on crape myrtle bush. I have white moldy looking matter...
Crape myrtles will get powdery mildew, a fungal disease. It sounds like yours has a bad case. You can spray a fungicide to prevent this fungus from infecting clean leaves, but a fungicide will not cure the leaves that are already infected.
Next year, you may want to spray a fungicide as a preventative. Keep a close lookout next year, and as soon as you see one infected leaf, pull it off and spray all the rest with a fungicide labeled to kill powdery mildew. Never spray when bees are visiting blooms. Spray before it starts blooming.
Try to get your shrub as much sun as you can and prune it to improve air circulation if the foliage has gotten very thick.