The Bartlett pear is very susceptible to fruit damage. Factors Affecting Abundance Failure to apply effective prebloom sprays with thorough coverage can result in a buildup of pear blister mite populations. The adult mites typically enter the second or third bud scale in August or September and spend the winter there. When foliage comes out in the spring, they become active, migrate to the tender leaves, burrow beneath the epidermis of the undersurface and start feeding. The eggs are laid in the fall and the young remain in the gall until they mature.
Adults leave the gall through a minute opening in the underside.
They migrate to new leaves and start new blisters. Reproduction is continuous and new galls are formed throughout the growing season. In late summer and early fall, the adult mites seek shelter for the winter beneath the outer bud scales. Monitoring When the foliage comes out in the spring, inspect the undersides of pear leaves for incipient blisters. The blisters will appear as small, greenish pimples that take on a reddish color and later turn brown.