Likely the crape myrtle scale that has been spreading out of the Richardson area for the past few years. Can't tell from the focus, but those white spots are the right size for scale and the black colored bark from the sooty mold that grows on their secretions is another symptom.

We've had only very modest results from topical treatments. However, our ant and lady beetle populations responded to knock back the initial infestations to a tolerable level. Systemic pesticides are said to work and would be our next line of defense.