I have a young crepe myrtle tree in full sun. It has developed a white moldy looking substance only on upper most new leaves. We live in zone 9. I have a drought resistant garden. There are small stones under tree that acts as a cover to retain moisture. No flowers yet. I sprayed it with deer defense.??? Thank you for your help! Genevieve
Crep Myrtle Tree
Certified GKH Gardening Expert
It sounds like your tree has Powdery Mildew.
These links will help you.