Pearleaf Blister Mite, Eriophyes pyri (Pagenstecher)

I. Introduction: Pearleaf blister mite (PLBM), also known as pear bud mite, and also by the synonym Phytoptus pyri Pagenstecher, is most often seen in unsprayed trees. This species is part of a complex of related species (E. pyri complex), which has confused accounts of life history.

II. Hosts: This species of eriophyid mite is restricted to pear. Apple, quince, hawthorn, serviceberry, cotoneaster, mountain ash and other related species have also been listed as hosts, but this reflects the clouded nature of the species complex.

III. Description: The bodies of these eriophyids are elongate and wormlike. The body length is 1/100 inch (200-240 microns; 0.2 mm). Other details have been published separating it from other eriophyids, but these will not be seen without a compound microscope. While in the bud, mites are white; later in the season they assume a pinkish color.

IV. Biology: PLBM has two general types of life cycle; this may reflect different geographical strains or species. In some areas (California, South Africa), a bud cycle exists which can cause up to a 25% reduction of production. In eastern North America, with its conditions of higher humidity, the leaf blister cycle is much more common. These differences relate to summer aspects of the life cycle. In both cycles, mites overwinter under buds. Only the blister form will be discussed further.

No reproduction or feeding occurs during winter in the buds. Mites begin to feed and oviposit as buds swell in the spring. Blisters begin to form at the cluster bud stage, on leaves 1/20 - 1/5 inch (1-5 mm) long. After 1-2 weeks, blisters begin to form small holes. Mites enter these holes and begin egg production. Usually only one female enters each blister. If present in fruit buds, feeding on floral parts will cause fruit blisters. Females produce 7-21 eggs each. In cooler weather, about 18 days are required for development; only 5-8 days are required in warmer weather. There are 2-3 generations per year. Activity ceases during June, July and August, resuming when cool evenings return. Mites return to buds from September to November.

V. Injury: This complex causes blisters on the undersides of pear and apple leaves, especially younger foliage, usually in a row along the midvein (Plate 93). The blisters are tiny green swellings at first, later expanding and turning red. These blisters eventually turn necrotic and brown (blisters that are not invaded by mites remain green). The leaf epidermis is loose and wrinkled on the underside of the leaf, resembling a blister. The blisters may coalesce, forming larger blistered areas along the midvein. The leaf blade may turn yellow, leaving a dark band along the midvein, dark green on the top and brown on the bottom of the leaf. Small blisters may also occur on stems and around the fruit calyx. This may cause fruit drop, but this is usually less common than the foliar injury. Leaf injury can result in small, sparse leaves.

VI. Monitoring: Watch for blistering from PLBM on leaves from cluster bud through late season. No thresholds are currently available from PLBM. If a damaging population were detected, control would be achieved in the next dormant spray.

VII. Management: Superior oil during the dormant or delayed dormant period. AgriMek plus oil before leaves harden.  Lime sulfur may also be applied in the postharvest period.

Additional sources:
University of California, Penn State University, British Columbia, Cornell University.

Back to Pear page
Back to Mid-Atlantic Regional Fruit Loop