Pear Blister Mite and Pear Rust Mite
Description and life cycle
Pearleaf blister mite adults are white to light red and extremely small (1∕100 inch). The body is sausage-shaped. Nymphs resemble adults, but are smaller. This species causes brownish blisters that appear on the undersides of leaves and fruit. On pear trees, blisters first appear as small greenish pimples that become reddish, then brown. They may cover the lower leaf surface.
On developing fruit, early feeding causes depressed russeted spots surrounded by clear halos that look like blisters. Since these mites do not move very quickly or very far, their infestations are often confined to single trees or even single branches. Pear rust mite is similar in appearance to blister mite, but the injury is characterized by a smooth russeting of the fruit.
Adult blister mites enter bud scales in August to September to overwinter. They become active at bud break, migrate to the tender, new leaves, and burrow beneath the epidermis of the undersides of leaves to feed. This results in a gall, or blister, in which the eggs are laid. The nymphs remain in the blister, emerging as adults to migrate a short distance to form new galls.
Monitoring and management
Examine terminal and fruit buds for mites during dormant and again just before bloom. During the summer, examine shoot foliage and the calyx end of developing fruit. Spray applications of recommended chemicals at delayed dormant or prepink should provide a good control of blister mite. Specific chemical recommendations for home gardeners are in Fruit Production for the Home Gardener, and recommendations for commercial growers are in the Penn State Tree Fruit Production Guide.