From Jamie Crist:
We have planted a number of crape myrtle trees over the years in our community and have enjoyed the beautiful blooms in the summer. Unfortunately, they are under attack by crape myrtle bark scale. This is a grayish-whitish bug that sucks the sap and nutrients from the tree. They excrete honeydew, a sticky mess that attracts flies and bugs and can lead to a black fungal infection.
Treatments are available from local arborists and tree companies. Remedies you can use at home are also available, though they can also affect other insects. Bonide All Season Horticultural & Dormant Spray Oil for Organic Gardening is available on Amazon. This can be combined with a tree drench treatment that is mixed with water and poured around the tree in the spring.
Check out the recent Washington Post article for more information: https://www.washingtonpost.
Other resources include: https://thegoodearthgarden.
https://extension.umd.edu/
I have informed the county about the problem and am waiting to hear back to see if they would consider treating them. Avoid further pruning at this time, as it can make the trees more vulnerable to infection.