Blister, bud, erineum, gall, and rust mites—Eriophyidae family
Pest Eriophyidae mites (commonly called eriophyids) include various Aceria, Aculops, Eriophyes, Phytoptus, Trisetacus, and Vasates species. These elongate, tiny mites cannot be seen without magnification of at least 20×. Most pest species feed on perennial hosts.
Adult eriophyids are about 1/120 inch (0.21 mm) long and difficult to observe with a high-powered hand lens. A dissecting binocular microscope or similar magnifier is needed to clearly see them. Generally it is their damage as described below that is the obvious clue to the presence of eriophyids.
Adult and immature eriophyids have four legs. The legs appear to be coming out of the head, which is at the wide end of the body. The body is carrot shaped or wormlike and commonly pinkish, yellow, or whitish. The tiny, pale eggs are hemispherical.
One detection method is to place infested plant tissue in a container with 90% ethyl alcohol. Shake this for about 10 seconds so tissue is thoroughly coated, and eriophyids are killed and dislodged. At a magnification of at least 20×, examine the fluid for pale, elongate eriophyids.
Eriophyids develop through 4 life stages: egg, protonymph, deutonymph, and adult. Adult females lay about 50 eggs during their life span. As temperatures cool in the fall and host leaves drop or the plant becomes dormant, eriophyids move to bark crevices and buds to overwinter. When host buds begin to develop and swell in late winter and spring, eriophyids begin feeding and reproducing.
Egg to adult development occurs in about 10 to 14 days when temperatures are warm. Eriophyids have multiple generations per year.
Eriophyids commonly blister, discolor, or distort flowers, leaves, or shoots. Although this damage mars plant appearance and may reduce yield on fruiting hosts, most eriophyids do not seriously threaten the health of garden and landscape plants and can be tolerated.
Hosts of eriophyids include aloe, bermudagrass, caneberries, citrus, cottonwood, fuchsia, garlic, grape, linden, nectarine, maple, oak, olive, onion, peach, pear, persimmon, plum, poplar, privet, tomato, walnut, and willow. Eriophyids are named for a primary type of damage they cause, such as blister mites, bud mites, gall mites, and rust mites. For example, fuchsia gall mite (Aculops fuchsiae) distorts fuchsia blossoms. The cottonwood gall mite (Eriophyes parapopuli) causes dark, warty, woody swellings on twigs near the buds of cottonwoods and poplars. Feeding by erineum mites, such as live oak erineum mite (Eriophyes mackiei), causes pale, felty, or hairy patches of distorted leaf growth called erineum.
No controls are recommended for most eriophyid mites. Naturally occurring predators are believed to sometimes be important in their management. To allow natural enemies to be more effective, control ants, minimize dustiness (e.g., periodically hose-off small plants), and avoid the application of miticides and broad-spectrum, persistent insecticides. See Protecting Natural Enemies and Pollinators for more information.
Eriophyids can be difficult to control with pesticides. They are commonly protected from sprays by their feeding location enclosed in buds and distorted tissue. By the time tissue grows and damage becomes apparent, the mites may no longer be abundant or present. Where pesticide will be applied, it may be best to delay application until the next growing season and spray terminals as new growth develops, when buds swell before they open. Potentially effective miticides available to home gardeners include horticultural oil, neem oil, and wettable sulfur. Do not apply oil within about 3 weeks of spraying sulfur or plant damage can occur.
For more information see The Eriophyid Mites of California (Acarina: Eriophyidae) and An Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites in North America .
Adapted from the publications above and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
Distorted, discolored leaves from feeding of aloe wart mite.
Blackberry drupelets that failed to develop mature color due to feeding of redberry mite.
Swellings on walnut leaves from walnut blister mite.
Swellings and felty masses on oak leaves from feeding of live oak erineum mite.
Bronzing of leaves from feeding of pear rust mite.