Unfortunately this has become quite a common condition across the state in the past few years, probably due in part to the widespread planting of this species. The white material is an insect called Crapemyrtle Bark Scale, which feeds on sap through the bark. The black material is fungal, but not a health threat to the plant (as it does not cause plant infections/disease); it's called sooty mold. You can learn about each on the linked pages.

Essentially, manual removal or insecticide treatment are the two options for controlling scale populations. As the scale are reduced, the sooty mold will go away on its own, because its source of food (honeydew produced by the scale, which is mentioned in the sooty mold web page above) will be waning as well.

This scale insect doesn't tend to kill crapemyrtle by itself, but it does add to tree stress, and might contribute to reduced flowering as the population builds. (In addition to contributing to a heavier coating of the unappealing black mold.) If you prefer to avoid insecticide use, your only recourse is to try to carefully scrub off the scale while not cutting into the bark. Otherwise, one or more insecticide products may need to be used, either by yourself or a hired professional. The selection of ingredient(s) and the timing of its application will determine how much of a risk the treatment may pose to pollinators or other beneficial insects (like scale predators).

Miri

Hi Miri,

You're welcome!