European Red Mite

The European red mite overwinters in the egg stage on twigs and branches. The red orange eggs have a long spike that is visible with a hand lens. Eggs hatch in early spring when the walnuts leaf out. Immature mites are bright red; adult females have a brick red, globular body with four rows of long, curved hairs arising from white dorsal spots. Newly molted mites may appear greenish. Adult males are brownish and smaller than the females. European red mites produce little or no webbing.

Usually red mite numbers build slowly during spring and do not become damaging until summer. They have multiple generations each season.

European red mites feed on the cell contents of leaf tissue. Initially, the feeding causes light stippling of the leaves. Prolonged feeding by high numbers of mites gradually gives leaves a bronzed appearance. Feeding by European red mite does not result in leaf drop, as does feeding by webspinning mites, but severe repeated bronzing of leaves for several years can reduce nut yields significantly. Damage by European red mite is generally rare, but damage is more common in cooler coastal areas than in hot, inland orchards.

European red mite can serve as a food source for predatory mites early in the season and help numbers of beneficial mites develop to levels sufficient to assist in controlling webspinning spider mites. A pesticide application is not recommended for low to moderate numbers of this mite.

In low numbers, the European red mite can be beneficial by providing a food source for predatory mites in spring. These predators can build to numbers that may be sufficient to control webspinning mites, which appear later in the season. The other predators described in the section on webspinning mites also attack European red mite.

Biological control and sprays of narrow range oils can be used in an organically certified crop. Caution should be taken when applying oils in walnuts to avoid injuring trees (see narrow range oil comments in the table below).

Look for European red mites during the dormant period by examining leaf and growth scars on twigs for clusters of red eggs. To combine monitoring for European red mites and other pests see DORMANT MONITORING. A dilute, delayed-dormant oil spray may aid in the control of European red mite. (Do not apply oils to walnut during dormant season.)

During spring, look for buildup of European red mite numbers and stippling or bronzing on leaves, especially in the shady, central parts of trees. You can check for European red mites when sampling for webspinning mites. Because damage by this mite is rare, no damage threshold levels are available to determine when to treat. Avoid spraying low to moderate levels of European red mites because they can be important in maintaining predators of other mites.