This is an infestation of Spiny Witchhazel Gall Aphid (Hamamelistes spinosus). During its life cycle, the aphid alternates between two host plants: witch hazel (Hamamelis spp.) and birch (Betula spp.). The feeding by these aphids causes corrugations and furrows in the leaves. Affected leaves may turn yellow and may prematurely fall off of the tree.

Most often, control of these aphids is not necessary. Many natural predators such as ladybird beetles, syrphid flies, soldier beetles, and parasitic wasps are active at this time of year and usually move into the area to reduce the aphid populations naturally. If your birch is new/young and populations are high, you can use a low-impact material like horticultural oil to minimize the impact on the beneficial insects that are present. There is more information on the following page of our website.

https://extension.umd.edu/resource/shade-tree-galls

Marian