There are several options for suppressing Crapemyrtle Bark Scale populations: manual removal (scrubbing off the scale you can reach, as long as you don't abrade the bark itself), topical insecticide sprays that kill scale on contact (like horticultural oil used when the crawlers are active), and systemic insecticides that are absorbed by the plant and ingested by the scale as they feed. The final category should be a last resort, as such chemicals might contaminate the flower nectar or pollen weeks or even months after an application, risking pollinator health.

You can learn about the life cycle (which is still being studied) of this scale on the page linked above. Crawlers are the most vulnerable life stage of scale insects, so treatments that target them are not only more effective, but can be chosen to be lower-risk for other insects as well. If a systemic is used, you will likely need to hire a professional (certified pesticide applicator) as one class of chemicals in that group are only legal for a licensed person to buy and apply in Maryland. Those chemicals may risk pollinator health if they visit the blooms of a plant that has been treated (even weeks or months after the application).

Fortunately, there are several naturally-occurring predators and parasites of scale that keep their numbers in check, and we've even seen them nearly wipe out a decent-sized population of scale on a tree without intervention.

If you use one or more types of pesticides, the timing of application will greatly depend on the chemical chosen. This scale species has at least two generations per year, and the timing of the crawler stage can vary a bit with the weather from year to year since it's dictated by how quickly or not the weather warms. Start by targeting the first generation and evaluate how effective the intervention seemed to be before deciding to follow-up with more treatments for subsequent generations. You may find that a knock-down for the first generation is sufficient to allow natural predation keep the rest in check.

Completely eliminating the scale is not necessary or feasible without likely having to use higher-toxicity insecticides that could harm other species. Even if successfully eradicated, the scale could always recolonize the tree(s) in a future year, as scale crawlers can "hitch a ride" on animals (like bird feet) or the wind to move about the landscape, even though they don't crawl far under their own power. With how abundantly Crapemyrtles are in Maryland landscapes, it's not surprising this invasive insect has spread so far around the state in just a few years.

Miri