Gall-forming eriophyid mites
Click for larger image Galls on silver maple (Acer saccharinum) caused by an eriophyid mite (Acari)

Eriophyid mites, an unusual family of mites that only have four legs, cause most galls caused by mites. Typically, adult mites as well as other members of the arachnids that includes spiders have eight legs. Eriophyd mites are carrot-shaped with the legs on the wider end (the head). They are microscopic and a good dissecting microscope is required to see them. The characteristic gall they cause on a particular plant species, however, can usually establish their presence. (Note: one group of eriopyid mites, the rust mites, do not cause galls. Their feeding on leaves and fruit results in a bronzing or russetting of the leaves or fruit.)

Damage of gall-forming eriophyd mites can be placed into on of eight groups based on the appearance of the galls: blister, leaf-curling, pouchgall, fingergall, budgall, witches broom, erineum, or flower or fruit distorting. (Erineum galls result from the enlargement of plant hairs on the leaf.)

Integrated Pest Management Strategies

1. Live with the damage. Once galls are noticed nothing can be done to eliminate them. Most home gardeners would do well to consider their damage cosmetic and not initiate any control measures as control measures may actually increase the problem in the future by killing the mites natural predators as well.

2. Use sprays. In some cases where mites are a recurring problem, dormant oil sprays may provide some control. More rigorous controls may be required for crops grown for commercial sale where an unblemished appearance is required.

Organic Strategies

Strategy 1 is a strictly organic approach.

More images:

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Ash flower gall is caused by an eriophyid mite (Acari) feeding on the male flowers of ash trees (Fraxinus)
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Closer look at ash flower gall, caused by an eriophyid mite (Acari) feeding on the male flowers of ash trees (Fraxinus)
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Distorted, enlarged plant tissue of a male flower on an ash tree (Fraxinus) caused by the tree's reaction to the feeding of eriophyid mites (Acari)
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Distorted plant tissue of a male flower on an ash tree (Fraxinus) caused by the tree's reaction to the feeding of eriophyid mites (Acari)
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Distorted plant tissue of a male flower on an ash tree (Fraxinus) caused by the tree's reaction to the feeding of eriophyid mites (Acari); this gall is also fasciated or flattened
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Distorted plant tissue of a male flower on an ash tree (Fraxinus) caused by the tree's reaction to the feeding of eriophyid mites (Acari); this gall is also fasciated or flattened
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Bladder-gall on silver maple caused by an eriophyid mite (Acari), begins as small, green, wart-like growths that later turn blood-red
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Eriophyid mites (Acari) are responsible for many galls, like these galls on the males flowers of an ash (Fraxinus)
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Eriophyid mite damage (Aceria ferruginea) on American beech (Fagus grandifolia)
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Eriophyid mite damage (Aceria ferruginea) on American beech (Fagus grandifolia)
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Eriophyid mite damage (Aceria ferruginea) on American beech (Fagus grandifolia)


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