Tetranychus urticae
Pest description and crop damage Adult mites are about 0.06 inch long, have four pairs of legs, are greenish to pink or cream color, and have various-sized black spots on the body. Under warm conditions, spider mites move rapidly within the colony area. Damaged leaves become somewhat stippled on the upper surface and may turn brown or bronze with heavy damage. The undersurface of leaves may have a grayish cast due to webbing. Wilting, leaf deformity, tissue death, and abscission all may take place.
Biology and life history Spider mites have four stages of development: the round, somewhat translucent egg with a red dot; a six-leg translucent larval stage; an eight-leg nymph stage; and the eight-leg adult stage. A resting or quiescent stage occurs at the end of the larval and nymph stages. A generation may pass in as few as 5 to 7 days in midsummer, or in a month during cool periods. There are numerous overlapping generations each year.
Management-cultural control
Spider mites generally prefer hot, dry, and dusty conditions. Avoid activities that increase dirt or dust on plants such as excessive driving during dry conditions; or, dampen driving areas to prevent dust drift into crops.
Management-biological control
Spider mites can be controlled by many natural enemy arthropods, such as predatory mites, thrips, and ladybird beetles. Conservative use of broad-spectrum insecticides and miticides that kill these natural enemies can prevent spider mite outbreaks. Preserve refugia for predators of mites with living plant ground covers or conservation tillage.
Management-chemical control
- bifenazate (Acramite-4SC) at 16 to 24 fl oz/A (0.45 to 0.675 lb ai/A). Maximum of two applications per season. REI 12 hr. Retreatment interval 14 days. Toxic to birds, estuarine/ marine invertebrates and fish. SLN 24c WA-150003 (expires 12/31/2022). Washington only.
- propargite (Comite) at 32 to 48 fl oz/A (1.64 to 2.46 lb ai/A). Maximum of two applications per season. REI 9 days. Retreatment interval 14 days. Toxic to fish. Resistance Group 12c. Restricted Use Pesticide. SLN 24c WA-040019 (expires 12/31/2025). Washington only.