Crapemyrtle Bark Scale has multiple generations per year, though researchers are still studying life cycle details for Maryland and the mid-Atlantic, since they may differ from areas to our south where the scale has been present for longer.

Recommendations for control include treating the bark with dormant oil at a 2 to 3% concentration and possibly also (or instead) using a systemic insecticide sprayed on the trunk or soaked into the root zone ( the pesticides you mention). The systemic would have to be applied by a certified pesticide applicator since such products are unlawful for the general public to apply in Maryland - this is why you cannot find the products to use. The oil could be applied by anyone, but is also best reserved for application by professionals in circumstances where plants are large and spraying needs to occur over one's head.

Dormant oil sprays need to be used with careful attention to seasonal timing as well as weather conditions during and immediately after the application, both so they remain effective and so they minimize risks of plant tissue damage. Thorough coverage of all bark surfaces is very important for it to be effective, and more than one treatment may be needed to bring the population under control. Dead scale insects don't always fall off of their host plant right away, so a treatment may start to work without initially changing the appearance of the infestation. If you spray anything yourself, pay careful attention to the product label directions, which can vary from one product to another, even if using the same active ingredient.

Scale insects in this group produce sugary excrement called honeydew since they feed on plant sap, and this substance can be attractive to flies and wasps that you might see visiting a scale-infested tree. Beneficial predatory insects (ladybugs and others) can also be drawn to the scale as prey, which fortunately the dormant oil will avoid harming. As the scale die off, the honeydew on the crapemyrtle or surfaces below it will gradually weather off. The sooty mold (the blackish fungus that is growing on the honeydew residue) will also go away in time without any direct intervention. This fungus does not infect the plant and merely grows on the sticky surfaces, so is only a temporary cosmetic problem.

Dormant oil is simply regular horticultural oil that is used at a slightly higher-than-typical concentration. Regular horticultural oil is sometimes referred to as "summer rate" oil to better distinguish between it and the dormant rate. Its lower oil concentration is better tolerated by foliage. During the dormant season, deciduous plants won't have that issue, having shed leaves. You would need to check the label for temperature recommendations to apply the dormant oil and seeing that they aren't leafed out yet it is probably fine, meaning it won't burn the leaves.

However, applying horticultural oils well can be tricky, which is why professional equipment tends to be more effective and somewhat safer; a professional applicator will also have the protective gear they need to apply it safely, particularly when spraying overhead. Factors impacting how well the treatment works include spray droplet size – fine mists from a high-pressure sprayer coat and stick to the plant surfaces more evenly than larger droplets from most over-the-counter pump or hose-end sprayers. Plus, the container usually needs to be kept well-mixed during spraying so the application doesn't end up too watery or too oily.

Horticultural oil is in the category of contact insecticides, meaning it must directly contact the pests it needs to control. Fortunately, scale barely move, so as long as bark surfaces are thoroughly coated, the oil should serve to deteriorate the scale's protective waxy shell and smother the insects underneath. The alternative treatment, a systemic, is a type of insecticide that the plant absorbs and is then ingested by the feeding insects. Since some of these chemicals could also make their way into nectar, they need to be chosen carefully to protect pollinators that visit the flowers. Even though crapemyrtle won't flower until summer, some systemic chemicals remain in the plant for months. A professional applicator should keep this in mind and choose a shorter-residual option where possible, or clip off the flowers that summer to prevent pollinator exposure. Crapemyrtle is not highly valued by pollinators, but honeybees and possibly others can visit the blooms.

Treating a plant in the "off season” with contact sprays does help to spare numerous beneficial insects, as can systemic use since the predators are not consuming the plant directly.

Let us know if you have further questions. 

Emily