Leaf Blister Mites
Pear-leaf and apple-leaf blister mites are microscopic worm-shaped mites in the eriophyid group. Adults overwinter under leaf bud scales and emerge with new leaf growth in the spring. They migrate to leaves and feed in colonies inside tiny blister-galls.
Newly formed leaf blisters are green and then turn brown as the leaves age; severe infestations can deform fruit and reduce tree vigor.
Watch leaves for blisters.
High populations can reduce photosynthesis and thus tree vigor. Lower populations can be tolerated.
Degree Day Model
Cannot be treated in summer. Horticultural oil, sulfur, or carbaryl in fall or spring is most effective.