Grape Erineum Mite

Grape erineum mites create distinctive blister-like galls on the upper leaf surface of host plants, with corresponding hair-like or velvety patches on the leaf undersides. In Western Washington gardens, Mahonia species develop these galls starting in late spring as mites feed underneath the leaf cuticle. The galls can be reddish, yellow, or brown; affected leaves may drop prematurely. The microscopic mites live inside the galls and remain invisible.

Remove heavily galled leaves by hand during early to mid-summer before mites disperse. Mahonia tolerates this pruning well. Water plants at soil level to reduce leaf wetness. Sulfur dust applied at first galling sign in spring may suppress early populations if applied every 10 to 14 days. Cultural management addresses the primary concern since damage is cosmetic.