Hi Bettie, 

The crepe myrtle has scale. Crapemyrtle bark scale (Acanthococcus lagerstroemiae) is a non-native type of soft scale insect that can be difficult to manage as their waxy body covering shields them from predators and certain pesticides.

Your tree is relatively small, and does not appear to be heavily infested, so it should be able to recover without problem. You will want to take a hose or pressure washer and spray off the white bumps on the tree bark. If the hose does not do it alone, use a stiff scrub brush to help. By exposing them this way, they are vulnerable to predators. 

More information about scale and its management can be found on the link above. 

Jamie