This eriophyid mite (family Eriophyidae) is named rust mite on oranges and silver mite on lemons. It can occur on all citrus varieties. It is a sporadic pest in most growing areas and occurs primarily in southern coastal areas of the state. Note that numerous species of mites can occur on plants.

Identification

Citrus rust mites are less than 1/100 inch (0.25 mm) long. A magnification of at least 20× is needed to see them. They are carrot or wedge shaped, tapering at toward the rear. Adults and nymphs have 4 legs at the front (wider) end near the body. Their coloration is pale brownish to yellow.

The minute eggs are spherical and translucent to whitish with a smooth surface. Eggs are about one-fourth the length of adults. They occur singly or in groups of several in depressions on fruit, leaves, or small twigs.

Life Cycle

Citrus rust mite develops through 4 life stages: egg, protonymph, deutonymph, and adult. The life span of an adult female is about 2 to 3 weeks, during which she deposits about 1 to 2 eggs per day. Highest abundance on fruit occurs from late spring through summer, but mite feeding on fruit continues during fall and early winter. During warm weather egg to adult development is completed in about 7 to 10 days. Citrus rust mite has many generations per year.

Damage

The mite and its feeding damage generally occur on the outside surface of fruit that is 1/2 inch or more in diameter. Feeding damages rind cells and causes the fruit surface to become silvery on lemons, rust brown on mature oranges, or black on green oranges. Most damage occurs from late spring to late summer, but does not hurt the internal quality of the fruit.

Solutions

Predaceous mites, dustywings, and mite midges prey on citrus rust mite. It is not known if these are important in the biological control of this pest, but natural enemies are responsible for preventing many potential pests in citrus from becoming a problem. To improve the effectiveness of biological control, control ants, minimize dust (e.g., periodically hose off small trees), and avoid the application of broad-spectrum, persistent insecticides and miticides for all citrus pests. See Protecting Natural Enemies and Pollinators for more suggestions.

No control is needed in gardens and landscapes as the feeding of citrus rust mite causes only aesthetic damage to the rind. If the rust mites are abundant and marring of fruit skins is intolerable, micronized or wettable sulfur can be applied. Note that spraying sulfur during hot weather can damage foliage, so application during November to early May is recommended. Do not apply sulfur within 60 days of spraying horticultural (narrow-range) oil and vice versa or plant damage may occur.

References

For more information see Citrus Rust Mite (PDF).

Adapted from Integrated Pest Management for Citrus, University of California Statewide Integrated Pest Management Program (UC IPM).