Eriophyid Mites

Blistered leaves and warty twigs are signs of eriophyid mites.

Eriophyid mites are a family of microscopic plant parasites that include blister mites, gall mites, bud mites, and rust mites. While you will probably never see them without a 20x hand lens, at 1/100” in length, they can be a translucent yellow, pink, white, or purple, with two pairs of legs up near the head.

Rust mite (Eric Erbe, USDA) Public Domain

Symptoms of eriophyid mite feeding include:

• Woody, wart-like swellings on twigs
• Raised blisters on the leaves
• Scabbing
• Leaf curling
• Leaf silvering and bronzing
• Brooming (weird clusters of tiny stems that burst out in all directions)
• Deformed leaves, buds, catkins, stems, fruit, and flowers
• Bud or flower galls
• Chlorosis and stunting on conifers
• Fruit russeting

Galls on cherry leaf from eriophyid mite feeding (Beatriz Moisset) CC BY-SA 4.0

Blister mites commonly attack beech, boxelder, cottonwood, elm, maple, live oak, walnut, willow, poplar, roses, privet, and alder. Unfortunately, they also feed on tomatoes, peach, apples, pear, and grapes. I have also heard of them on plum trees in some warmer areas. Eriophyid mites spread on the wind, so there isn’t much you can do to stop them from showing up in your landscape. Luckily, the damage they cause is mostly aesthetic and poses no real threat to otherwise healthy plants. That being said, who wants warty leaves or scabby twigs? Also, eriophyid mites may also carry viruses that can cause real damage.

Insecticidal soaps and horticultural oils can be used on heavy infestations, but simply removing affected leaves, buds, flowers and twigs is really all that’s needed. Sulphur and neem oil have also been shown to be effective. Before you work too hard at getting rid of these minor pests, you may want to keep in mind that the eriophyid mites are a favorite food of predatory mites and other beneficials.

Isn’t it nice to know that some problems in the garden are not big enough to worry about?