Knowledgebase
Black Locust Tree infestation #757509
Asked June 21, 2021, 2:36 PM EDT
Calvert County Maryland
Expert Response
Hello Josh,
These are aphids (and the white flecks are their shed skins), and while often numerous, their feeding rarely causes serious problems for plants, especially trees. Many beneficial insects prey on aphids, and they should catch-up to the infestation soon to reduce their numbers. We see at least one aphid "mummy" in the picture, so some are already beginning to work. (See the photo of an aphid mummy under Management - Biological on this page.)
Spraying, even with an organic pesticide, risks killing the beneficial insects along with the aphids. Since the impacts of aphid feeding are minimal to negligible for the locust, we don't recommend any treatment with pesticides. If the tree is young enough to reach, you can try blasting off aphid colonies with a strong jet of water, but it's otherwise not necessary.
Miri