Spider Mites

How to thwart an infestation of spider mites.

January 30, 2013

Family Tetranychidae

Adults: minute, eight-legged, 1/50-inch mites with fine hairs on body; reddish, pale green or yellow; most, but not all, species spin fine webs. Nymphs: similar to adults, but smaller; early stages with six legs. Found throughout North America. Cyclamen mites are similar pests.


Adults and nymphs suck juice from cells on undersides of leaves of many food crops, ornamentals, and fruit trees. Plants are weakened, leaves may drop, and fruit may be stunted. Early damage to leaves appears as yellow-specked areas, with or without webbing, or leaves turn yellow or white with brown edges; webs may cover leaves and growing tips.

Life Cycle
Eggs or adults overwinter in bark crevices or garden debris, emerging in early spring. Eggs hatch in 2 to 3 days, nymphs develop to adults in 7 to 10 days. Many overlapping generations every season; reproduction continues all year in greenhouses.

Spray fruit trees in late winter or early spring before or just as buds swell with horticultural oil (dormant-season dilution) to kill overwintering eggs; in garden or greenhouse rinse plants with water and mist daily to suppress reproduction of mites; release predatory mites Metaseiulus occidentalis on fruit trees, Phytoseiulus persimilis or similar species in large-scale plantings of vegetables, strawberries, and flowers; as a last resort, spray insecticidal soap or neem.

Photo: Eric Coombs, Oregon Department of Agriculture, Bugwood.org