Recognise sycamore gall mite

28th July 2021

Recognise sycamore gall mite

These red, pimple-like bumps on the leaves of young sycamores are caused by tiny mites which overwinter in bark crevices and then emerge in spring to feed on the unfurling leaves. As they pierce individual cells to feed, the surrounding cells are stimulated to divide,  enlarging and forming the prominent red galls. The mites lay eggs inside the galls from mid-May and several generations can occur over a season, finally exiting the leaves in autumn to overwinter in the bark. Although it disfigures a sycamore, it does no permanent damage to the tree.

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