Crapemyrtle bark scale
I believe this is a scale infestation but crepe myrtle bark scale is an insect found in southern states. For a positive identification on the exact type of scale shown here bring a sample of branch with the scale attached into our office. Correct ID will mean spraying with the appropriate chemical at the appropriate time.
Feel free to contact our office if you have other questions.
Let me know if I can help you further!
Jefferson County Cooperative Extension Service
200 Juneau Drive
Louisville KY 40243