Crapemyrtle Bark Scale - Ask Extension
I'm pretty sure my crapemyrtle has bark scale. It had a very heavy infestation earlier this summer and I scrubbed off what I could using soapy water a...
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Crapemyrtle Bark Scale #807203
Asked August 20, 2022, 1:25 PM EDT
I'm pretty sure my crapemyrtle has bark scale. It had a very heavy infestation earlier this summer and I scrubbed off what I could using soapy water and a long handled brush and ladder. But now it appears to have come back. I've read online about using a soil drench of a systemic insecticide containing imidacloprid, but my understanding is that neonics are banned in Maryland. Is there anything that we can apply now to kill the insects? We can wash off what we can again, and apply dormant oil in the winter, but I'm also looking for something we can do now to kill them and prevent the buggers from infecting our neighbor's crapemyrtles. Would appreciate any advice!
Montgomery County Maryland
Expert Response
We agree this is Crapemyrtle Bark Scale, and while systemic insecticides can be part of the toolbox used to control them, you are correct that some ingredients are riskier to pollinators and non-target insects than others. Fortunately, relatively few insects feed on crapemyrtle or visit its flowers, though we have heard of some birds eating their seeds in winter. We suggest you work with a certified pesticide applicator to determine what to use and when, especially since they will have more effective application equipment than what most of the general public can easily find. People with this certification (which is granted by the MD Dept. of Ag.) tend to work for landscaping or tree-care companies, are arborists, or are independent IPM consultants (Integrated Pest Management, where insecticides are the tool of last resort).
True, certain pesticides (such as the neonicotinoid class of insecticides in Maryland) do require that a certified individual purchase and apply them. Not all systemics last long enough to remain in nectar or pollen the season after application, but it will depend on the product used as well as the application timing. An Insect Growth Regulator (IGR) is another category of insecticide that could be employed to suppress the population by preventing the scale from maturing and continuing to breed. Both of these approaches take time to work and won't result in a marked reduction in the population right away; good control of an entrenched scale population can take one or more years, and it's possible they will spread to neighboring properties in the meantime, because that's fairly unavoidable. The neighbors can inspect their crapemyrtles periodically to monitor them for scale; if present even in smaller numbers, it would make sense to have crapemyrtles across several neighboring yards treated at the same time to squash an outbreak if it's already spread beyond your property.
We have circled what we think is a scale predator on the bark in one of your photos [attached]. The larvae of certain lady beetles (ladybugs; Hyperaspis probably) look somewhat like mealybugs or scale due to their white waxy covering, which allows them to blend in while consuming the scale insects, so we want to preserve them by not redoing a trunk scrub or using insecticidal soap or horticultural oil yet, which while relatively low-impact overall are still indiscriminate in what insects they harm upon contact.
Miri
True, certain pesticides (such as the neonicotinoid class of insecticides in Maryland) do require that a certified individual purchase and apply them. Not all systemics last long enough to remain in nectar or pollen the season after application, but it will depend on the product used as well as the application timing. An Insect Growth Regulator (IGR) is another category of insecticide that could be employed to suppress the population by preventing the scale from maturing and continuing to breed. Both of these approaches take time to work and won't result in a marked reduction in the population right away; good control of an entrenched scale population can take one or more years, and it's possible they will spread to neighboring properties in the meantime, because that's fairly unavoidable. The neighbors can inspect their crapemyrtles periodically to monitor them for scale; if present even in smaller numbers, it would make sense to have crapemyrtles across several neighboring yards treated at the same time to squash an outbreak if it's already spread beyond your property.
We have circled what we think is a scale predator on the bark in one of your photos [attached]. The larvae of certain lady beetles (ladybugs; Hyperaspis probably) look somewhat like mealybugs or scale due to their white waxy covering, which allows them to blend in while consuming the scale insects, so we want to preserve them by not redoing a trunk scrub or using insecticidal soap or horticultural oil yet, which while relatively low-impact overall are still indiscriminate in what insects they harm upon contact.
Miri
