Spinach seed-Twospotted spider mite

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 oval, somewhat translucent egg; 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-chemical control

  • propargite (Comite) at 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. SLN 24c WA-040019 (expires 12/31/2019). Washington only.