Although Crapemyrtle Bark Scale is widespread in Maryland and can stress trees and cause the sooty mold you've observed, we do not see scale in the photos sent. (Feel free to send more if you have another area of bark with what you suspect are scale.) The bark shown in the close-up has what appears to be lichen, which while uncommon on crapemyrtle due to the natural bark shedding trait it has, is not harmful and can be ignored. (The linked pages have more information.)

Sooty mold can grow on honeydew from other insects, so perhaps there were either Crapemyrtle Aphids present in prior years or even Spotted Lanternfly nymphs or adults. Those aphids are specific to Crapemyrtle and are also quite common, though populations of lanternfly still vary a bit, although they are present in your county (and in much of Maryland, really).

Management options will depend on what insect was causing the sooty mold growth, but if scale was responsible, any treatment for them will likely also suppress any aphid populations at the same time. While a dormant oil (which is just a slightly more concentrated version of the summer dilution rate of horticultural oil) is one method of treatment for scale insects, it tends to require multiple treatments since it has limited impact each time, given the insects' waxy body covering that shields them from most sprays and predators. The goal of such a spray is to smother them and/or degrade their waxy "shell" to let them dry out and die. Dormant oil is used in winter because it won't risk "burning" foliage, but it might take more than a year's worth of treatment to get a high population under control. How often to spray depends largely on the insect's life cycle (in combination with what the product label instructs), since the most vulnerable stage in a scale insect's life cycle is the crawler stage, which are new hatchlings that don't have their waxy cover yet while they wander around. Using horticultural oil (neem being one kind) to hit the crawlers is the most effective approach, but since this scale species is relatively new to the mid-Atlantic, we're still researching exactly when each generation (of the two or three this species has each year in our area) occurs based on temperature trends.

If you opt to hire a certified pesticide applicator, especially once who has experience treating scale, they should be able to monitor a population to detect when crawlers have emerged, and then treat for you. Even though horticultural oil is a lower-risk pesticide compared to others, it must be applied thoroughly and evenly over all areas the pest inhabits, so on larger plants, usually this is best accomplished by a professional whose spray equipment will be of better quality or calibration to generate very fine droplets of the oil. (They also will have any personal protective equipment needed to spray a plant over their head.)

Systemic pesticides of any type might risk contaminating nectar and pollen in blooms (more research is needed on this), which is why the chemical class called neonicotinoids were regulated in Maryland. Several chemicals exist in that category, and not all remain in the plant for the same length of time. If used, for example, the buds/blooms could be cut off for that season to spare any pollinator exposure while the chemical worked to kill the scale population. When applied in soil drench form, the roots absorb the chemical and move it up in xylem (the tissues moving water upwards) to the branches above. Since xylem only flows upwards and not downwards, the chemical must be root-applied. Other systemic pesticides work by leaf or bark absorption and move in phloem, the sap-carrying tissues that can transport materials in any direction. Neonicotinoids are not the only systemic insecticide ingredients, and others may or may not work well on soft scale in particular (see what the label says, as soft scale and armored scale are not equally affected by the same systemics). If neonicotinoids were the most practical choice for treatment of a given plant, then a hired certified applicator could legally make the treatment for you.

We do not recommend drastic pruning unless you prefer to just remove the plant instead. Drastic pruning stresses the tree and, aside from potentially weakening branching and ruining its shape, might invite attack by an incurable pest like Ambrosia Beetle that bores into wood. If you do end up removing any of the Crapemyrtles, we recommend putting in native species in their place, since at least they may benefit wildlife more than the non-native Crapemyrtle, even though every plant species has a few pests and diseases it can be vulnerable to under certain circumstances.

It's hard to tell why canopy dieback might be taking place if the scale are not present. A high aphid population can be a nuisance but should not cause any serious dieback. If anything damaged roots, such as digging or an herbicide exposure (lawn weed-killer chemicals are a common culprit), that would explain it. While we are near the limits of cold tolerance for Crapemyrtle in Maryland, usually they don't have much issue with our winters, though a mild year that has a sudden cold snap can still injure even hardy species. There are so many cultivars these days that some are less hardy than others, but those on the market 30 years ago were more vetted for cold-hardiness at the time since many came out of the National Arboretum breeding program.

Extension doesn't collect information on landscapers or horticulture pest control professionals, though we do help to train IPM scouts, and the MD Dept. of Ag. is the agency that certifies commercial pesticide applicators. (Integrated Pest Management uses multiple techniques to manage pests before resorting to a pesticide, and also emphasizes proper pest ID and assessing each situation before deciding to treat, such as looking for indications of beneficial insect activity that is helping to suppress the pest.) Extension doesn't recommend any particular person or business (nor do we have a reference list of options), though some IPM-trained professionals are self-employed as garden consultants or may be part of a landscaping company. If you use social media or a neighborhood forum, you might be able to ask around for recommendations for someone who has experience evaluating Crapemyrtle or which has experience treating scale.

Miri