Family – Eriophydae

The pear leaf blister mite is an eriophyid mite. It came from Europe about 1870 and became a pest about 1902 in the United States.

Egg: The egg of the blister mite is dull white, oval and about 0.05 mm long.

Nymph: The immature stages resemble the full-grown mite, except in size.

Adult: The adult is white or light red and ranges from 0.16 to 0.25 mm long. The body is long and tapering to the rear. The front end bears the head with the mouthparts. Two pairs of legs are attached just behind the head. There are long hairs, or setae, on the legs and five pairs on the sides of the body. The covering of the mite is annulated so that it looks like about 80 narrow rings.

This mite is a pest of pear, apple and European mountain ash. It is a problem in all of the pear-growing areas of Canada and the United States.

Two distinct types of damage occur: fruit spots and blistered leaves.

These mites cause brownish blisters on the undersides of pear and apple leaves. On pear, the blisters appear as small, greenish pimples that soon take on a reddish color and later turn brownish. On apple, the first stages are pale yellowish and the blisters never become as red as on pear. The blisters, about 3 mm wide, may be massed together to nearly cover the undersides of the leaf surface. If you like at these with a hand lens, you will see many small mites. Heavy infestations cause blistering of leaves that can seriously impair leaf function.

Early feeding of the mites on the developing fruit causes depressed russet spots, which can be the most serious aspect of blister mite attack. The fruit is often deformed and misshapen. The presence of these oval russet spots, usually depressed with a halo of clear tissue surrounding each spot, is a characteristic symptom of blister mite attack. The Bartlett pear is very susceptible to fruit damage.

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 resulting irritation produces a thickening of the leaf tissue – a gall. 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.

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.

Effective cover sprays are necessary, especially in the prebloom stage, if there is a serious problem.