These are crape myrtle scale. They are quickly becoming a problem in some areas of Wake County.
They probably have 2 generations a year here and are more numerous and more difficult to control now (second generation).
Clemson, https://hgic.clemson.edu/factsheet/crapemyrtle-bark-scale/, suggests a few control strategies. Unfortunately, the most effective one is a soil drench w/ a systemic pesticide. The problem w/ systemics is that they kill all insects that feed on a plant, including bees and other pollinators feeding on nectar and pollen. The systemic can also be taken up by other nearby plants.
The females and crawlers must walk from plant to plant, so infection of nearby plants is slow.
I suggest you read the article from Clemson for a better understanding of the pest and possible control strategies.