Leaf Blister Mites
Hosts: apple, pear
Biology: Pear-leaf and apple-leaf blister mites are microscopic 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.
Symptoms: Newly formed leaf blisters are green and then turn brown as the leaves age.
Monitoring: Watch leaves for blisters.
Treatment Threshold: High populations can reduce photosynthesis and thus tree vigor. Lower populations can be tolerated.
Degree Day Model: None
Management Considerations: Cannot be treated in summer. Horticultural oil or sulfur in fall or spring is most effective.