Pearleaf Blister Mite

 Blistering of leaves on pear are often evident starting in early summer. By the time symptoms are noticed it is too late to control the mite. Luckily, damage from pearleaf blister mite does not adversely affect plant health unless it is under stress from another source. However, fruit can be damaged if the infestation is extensive, in which case, control is necessary.

Adult mites are very small, about the same size as rust mites, and cannot be seen without a 14 to 20X hand lens. The body is white, long and slender, striated, and with a few long hairs. Immature forms resemble adults but are smaller. Eggs are spherical and pearly white.

Pearleaf blister mites feed under the bud scales during winter and may cause buds to dry and fail to develop in spring. When buds start to grow in spring, mites feed on emerging leaves from green tip through bloom and also on developing fruit.

Feeding on fruit results in oval russet spots, usually depressed with a surrounding halo of clear tissue. These spots are 0.25 to 0.50 inch in diameter and frequently run together.

When damaged fruit matures, it is often deformed and misshapen. Leaf feeding causes small blisters, 0.125 (3 mm) to 0.25 inch (6 mm) across, which are first red and later turn black. Leaf function can be seriously impaired. Eggs are laid in the blisters and young mites feed inside the blister, thus they are rarely seen.

Most of the overwintering blister mites are found beneath the outer bud scales in October and November and are readily controlled with a fall spray of mineral oil.

The presence of any mites indicates the need for control. As the season progresses, control becomes more difficult. The use of pyrethroids may increase blister mite damage.

Mike Bauer is the horticulturist for Moose Valley Farms, a full-service garden center located in Naples at mile marker 495. Feel free to call them at 267-5108 or stop in if you have any questions.