Pear Rust Mite

Family – Eriophyidae

The pear rust mite is an eriophyid mite that is restricted to pears.

Egg: Eggs are spherical and about .05 mm long. When first laid, they are clear. They later turn white.

Nymph: The nymphs, which resemble the adults, have two instars.

Adult: The adult is about .05 mm long and wedge-shaped, with the widest part at the head end. The color varies from dull white to light brown.

The pear rust mite is restricted to pears.

Mite feeding on leaves causes leaves to turn brown or bronze. This injury may stunt the growth of young trees. On older trees, motes deeding on leaves cause minor damage compared with the greater effect of mite feeding on the fruit. Extreme russetting of the fruit surface rough and brown. This injury renders the fruit unsalable for the fresh and processing markets.

Early in the season, rust mites tend to feed at either the calyx or the stem end and cause a localized russetting in those areas. Feeding and russetting may spread over the fruit surface, with the intensity of russetting determined by the number of mites and the length of their feeding period.

Hot, dry weather favors a rapid buildup of this pest.

The mite overwinters as an adult female under leaf scars or bud scales or in small cracks on twigs. With the advent of warm weather, even before the buds break, these mites are feeding and laying eggs under the bud scales. As the blossom cluster expands to throw off the outer scales, the exposed mites start to migrate toward the developing bloom, resulting in a concentration of active stages in the calyx end of the nearly developed fruit. The young mites from the hatched eggs also feed on the flower stems just prior to bloom. By petal fall, they are feeding vigorously on leaves and at the calyx end of the developing fruit. Later they spread over the tree, also feeding on leaves.

Damages areas of fruit gradually russet or turn brown. In June, the first russetting shows mainly at the calyx end of the fruit, and most russetted fruit is usually on the sunny south or east side of the tree. Once the mites spread out over the tree in large numbers, succeeding generation (several during the season) move onto the fruit from the stem ends and, if not controlled, will gradually russet whole fruits. In July, some females begin to hibernate for the winter, but if the weather is hot and dry for long periods, the mites will go on feeding into August until cool weather occurs, at which time they will seek shelter and overwinter under leaf scars or bud scales.

In winter or very early spring, collect and open pear buds to determine the relative density and distribution of pear rust mites in the orchard. Later in spring, sample 25 fruit clusters in an orchard. Treatment is recommended if pear rust mites are found in five or more clusters. When examining clusters, use a hand lens with a magnification of 10x of higher, and make sure the area is well lit.

Prebloom and petal-fall sprays are essential to control this pest. Trees must be sprayed dilute from both sides and should be monitored for pear rust mite until harvest.