Pointing out spider mites
3 (1 = rare 5 = annual)
3 (1 = very little damage 5 = plants killed)
Active nymph and adult mites appear as tiny, eight-legged, yellowish to reddish specks. Plants attacked may have very fine webbing on or between the leaves.
Attacked cucurbit leaves are stippled with white and then brown specks. Damaged leaves usually appear dusty or bronzish; they may turn brown and drop from the plant.
Twospotted spider mites overwinter as mature females under ground cover and around the base of living plants. After mating, females lay 2-5 eggs per day on the underside of leaves. Each female lays up to 100 eggs. Eggs hatch in 2-6 days, and immature mites progress through 3 stages before becoming adults capable of reproducing. Development from egg to adult takes 7 to 20 days, depending on temperature. Successive generations develop throughout the growing season. Hot dry weather favors the development of severe infestations.
Mites are normally controlled by natural enemies. During hot, dry weather, the mites reproduction may outstrip the ability of the predators to control them. Previous insecticide spraying kills the natural enemies, making damaging infestations more likely. Scout for mites, particularly around field edges, during hot, dry weather. Holding a white sheet of paper under the foliage, strike the foliage with quick, hard blows to dislodge the mites onto the paper. Slower-moving mites that streak green when crushed are likely to be twospotted spider mites. Faster-moving mites that streak red when crushed are probably predatory mites. If predatory mites are numerous and plant damage is not occurring, treatment is probably unnecessary. Large numbers of twospotted mites with few or no predatory mites usually warrants control. Treatment usually is required only around field edges, but if mites are numerous, also check for areas throughout the field that may need to be spot treated.
Filed under plants: Vegetables
Filed under problems: Insects Damage