Ashflower gall

Distribution

Canada

Micro-habitat(s)

Damage, symptoms and biology

Most galls of deciduous trees are caused by mites so small that they are barely visible to the naked eye. Other galls are caused by some wasps, midges, and aphids. The mites insert their slender mouthparts into the leaf or flower tissue and suck out the plant juices. When feeding, they apparently inject a growth-promoting substance into the tissues which results in the formation of swellings or galls on the surface of the leaves or flowers.The effects of feeding and gall formation on growth are not well known but it is probable that they reduce the ability of leaves to produce foods and thus weaken trees to some extent. Severe infestations make the foliage unsightly.

Most of these mites overwinter as adults, hibernating in the crevices of the bark and beneath bud scales. When the buds begin to swell, the mites crawl to the opening buds where they feed and lay eggs. The eggs hatch in 7 to 10 days and the nymphs settle down on the young leaves. Galls begin to form around the nymphs shortly after they begin feeding, and within 2 weeks they are completely entombed within the galls. By early August, when full grown, they emerge from the galls and go into hibernation.

A very small mite, Eriophyes fraxiniflora Felt, sometimes causes the flowers of ash to become enlarged and distorted. This distortion results in unsightly masses on the twigs. Such galls turn black and remain on the trees throughout the winter. Trees are not likely to be killed but some dieback of the current year's growth may occur, resulting in deformed trees.

Main host(s)

American mountain-ash, apples, ashes, basswood, beeches, black ash, blue ash, elms, European ash, green ash, northern red ash, Oregon ash, poplars / aspens / cottonwoods, pumpkin ash, red ash, red maple, red oak, silver maple, sugar maple, trembling aspen, white ash