Prune and burn affected parts. With Phyllosticta, leaves will have reddish-brown spots bordered by darker zones, outside of which is a zone of dark red. There may also appear within the spots small, black fruiting structures of the fungus. This fungus causes cankers and twig blight on cotoneaster. Prune and destroy infected branches.
Powdery mildew is very common on crapemyrtle.
It is particularly active in the spring and fall months. Dust or spray with a recommended fungicide at first appearance of mildew. Dallas red is an old variety with good mildew resistance. Check on availability of newer varieties with mildew resistance. If needed, apply a recommended fungicide.