Grape erineum mite

Pest description and crop damage. This mite is similar in morphology to the grape bud and bud mites. It is microscopic, wormlike, and white-yellow in color. It overwinters between outer bud scales and bud tissue and feeds on leaves during spring and summer. The upper leaf surface becomes blistered, and the lower leaf surface of the blister appears hairy and white, almost resembling fungal growth. The lower leaf surface turns from a white color early in the season and progresses to yellow or brown later in the season. In severe cases, these mites may infest clusters in early spring. Although these mites are eriophyid mites and have the same genus and species as the bud mite, they differ from the bud mite in their biology, migration, and symptoms on the vine.
Biology and life history. Colonies of mites live in blisters (erinea) formed by their feeding on lower leaf surfaces. The blisters are comprised of masses of enlarged leaf hairs. These blisters protect mites from natural enemies and direct contact of pesticide sprays. As the population increases, some move to new areas or other leaves and form new erinea. From mid-August until leaf drop, there is a movement from the erinea back to overwintering sites beneath the bud scales.