European red mite—Panonychus ulmi
This spider mite (family Tetranychidae) is especially common on apple. It is occasionally abundant on Prunus species (e.g., almond and stone fruits), and walnut. It can occur on about 150 plant species including ash, black locust, elm, and rose, but it generally is not damaging to these other hosts.
Immatures of European red mite are red, except just after molting when they are bright green. The green color turns to red after the mites resume feeding. Adults are dark red and have a white spot at the base of each of six to eight hairs on the back.
Eggs are globular and red with many grooves extending from top to bottom. They have a slender stalk rising from the top center. Eggs resemble those of citrus red mite (Panonychus citri), except European red mite eggs lack the 10 to 12 threads radiating from the tip of the stalk to the leaf surface that occur on eggs of citrus red mite.
Similar-looking mites found in gardens and landscapes include southern red mite (Oligonychus ilicis), which can be common on broadleaf evergreens such as azalea, camellia, holly, and rhododendron. The similar citrus red mite occurs on many plants but is a pest only on citrus.
European red mite develops through five life stages: egg, six-legged larva, and eight-legged protonymph, deutonymph, and adult. The mite overwinters as eggs on roughened bark at the base of buds and spurs on smaller branches and twigs or in bark wounds. During the growing season, eggs are laid on leaves. Overwintering eggs are laid as early as August and as late as October and November, varying with the weather.
Overwintered eggs hatch in late winter or spring when hosts blossom. The immature mites migrate to leaves and feed on young foliage. Especially early in the season, European red mites are mostly found on the undersurface of leaves. Low temperatures in spring can prevent high populations from developing.
European red mite can complete 1 generation in less than 3 weeks when temperatures are warm. It can have 5 to 10 generations per year.
European red mite generally is damaging only on apples and less often on Prunus species. The mites' sucking feeding causes leaves to lighten in color, becoming whitish, mottled, or stippled. Prolonged feeding by heavy populations eventually causes leaf bronzing or burning and sometimes premature drop of leaves, which can result in sunburned fruit and reduced yield the following growing season.
Keep host plants adequately irrigated during warm weather to reduce the likelihood of a spider mite problem. Predators of mites generally keep European red mite abundance below damaging levels if the natural enemies are not disrupted, such as by pesticide application.
Western predatory mite and other predatory mites, such as Phytoseiulus persimilis, are the most important predators of European red mite. Green lacewings, spider mite destroyer (a tiny, black lady beetle, or ladybug), and sixspotted thrips are also important mite predators. To improve the effectiveness of biological control, control ants, minimize dustiness (e.g., periodically hose off small plants), and avoid the application of miticides and broad-spectrum, persistent insecticides for all pests. See Protecting Natural Enemies and Pollinators for more suggestions.
Insecticide application during the growing season is generally not necessary or advisable for European red mite. An exception can be on apple where horticultural (narrow-range) oil spray may be warranted during the delayed dormant period (when buds are swollen but not yet burst open); this time is just as the mite eggs are about to hatch. If the mites are excessively abundant during the growing season, wait and make an oil application when buds swell in late winter or spring. For more information, see Pest Notes: Spider Mites.
Adapted from Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
Leaf stippling from feeding of European red mite.
Adult European red mites have a white spot at the base of each hair on their back.
Eggs of European red mite.