Leaf blister mite

Leaf blister mites cause distinctive blister-like galls to form on the upper leaf surfaces of Sorbus species, with corresponding fuzzy or velvety patches visible on leaf undersides. The galls can be reddish, yellow, or brown in color; affected leaves become distorted and may drop prematurely. The microscopic eriophyid mites live inside the galls and remain invisible to the naked eye. Damage appears in late spring.

Remove heavily galled leaves by hand during early to mid-summer before mites disperse. Sorbus typically tolerates pruning well. Water plants at soil level rather than overhead to reduce leaf wetness. Sulfur dust applied at first galling sign in spring, repeated every 10 to 14 days, may suppress early-generation mites. Leaf removal and cultural control are primary.