ash leaf curl (Psyllopsis spp.)

A gall created by the larvae of several species of jumping plant lice (in the same family as the cuckoo-spit louse), that feed on ash leaves. The edge of an affected leaflet swells and folds or rolls towards the underside, either from the tip towards the base or from the side towards the midrib. The affected part withers and turns brown but the leaf does not fall

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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