Forest Pests: Insects, Diseases & Other Damage Agents

Ash Flowergall Mite - Aceria fraxiniflora Felt

Solomon, J.D.; Leininger, T.D.; Wilson, A.D.; Anderson, R.L.; Thompson, L.C.; McCracken, F.I. 1993. Ash pests: A guide to major insects, diseases, air pollution injury and chemical injury. Gen. Tech. Rep. SO-96. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 45 p.

Importance. - This eriophyid mite attacks male flower clusters, turning them into masses of lumpy, distorted galls. Infestations do little damage to trees, but the galls are unsightly and may markedly detract from the appearance of ornamentals. The mite is distributed throughout the United States and southern Canada. Identifying the Mite. - The mites are minute, about 0.5 mm long, soft bodied, wormlike or spindle shaped, and white to straw colored. They are so small as to be largely invisible to the unaided eye and are frequently overlooked, even with a 10x magnifier.

Damage James Solomon, USDA Forest Service

Identifying the Injury. - Feeding by the mites on the male flower clusters causes swelling of the tissues. Flower stems elongate, pedicles of individual flowers often fuse, and all parts curl and twist. Infested flower clusters become irregularly branched, fringed, gall- like masses. Galls are initially green but darken and become black later in the season, and many persist until the following spring.

Biology. - In the spring, overwintering females move to the developing flowers to feed and deposit eggs. Nymphs live and feed in protected crevices of the gall tissue. There are several generations during the spring and summer. In the fall, fertilized females move to bark crevices and beneath bud scales to overwinter.

Control. - High-valued trees can be sprayed in the early spring as soon as they begin to flower.

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