My mother's crape myrtle mysteriously dropped all of its leaves overnight. Have you ever heard of this? If so, what might be the problem?
Why Would a Crape Myrtle Drop All Its Leaves Overnight?
Certified GKH Gardening Expert
Crepe Myrtle is a deciduous tree and early Autumn weather will trigger leaf drop.
If the tree drops it's leaves outside of the Autumn time frame, it could be a fungus issue.
If you suspect fungus and not due to Autumn weather, rake up all leaves and dispose.
Spray the tree with Neem Oil. Use a 70 % solution and add 2 Tablespoons to a gallon of water. Spray the tree throughly.
Air circulation is key to good tree health.
Here are some links for you with more information.