Grapeleaf blister mite

Grapeleaf blister mite is 0.2 mm long, white or creamy and worm-like with two pairs of legs at the anterior end of the body. Blister mite and bud mite, although morphologically similar, can be easily distinguished by the damage they cause.
Blister mites feed on the under-surface of leaves and cause very obvious blisters on the upper surface of leaves and white or brown hairy growths within the raised blisters on the lower surface of leaves.
Blister mite over-winters inside buds, but after budburst they move onto leaves to feed and complete their lifecycle within the hairy blister. Damage can be unsightly but does not usually have economic consequences.