Twospotted Spider Mites

Twospotted spider mites suck the contents of plant cells, causing bleached, stippled, or otherwise discolored foliage. They also make silken strands on plant parts, especially when populations are high. The mites have globular bodies that are 1/50 inch (0.5 mm) or less in diameter. Adults have two dark blotches on the body and overall coloration that varies from gray to green or yellowish. Overwintering females may turn pink to orange during fall to early spring.

Spider mites develop through five life stages. Females lay round eggs that hatch into six-legged larvae. Larvae develop into eight-legged protonymphs, then deutonymphs, then adults. Spider mites have many generations per year and their abundance can increase rapidly when temperatures are warm. Egg to adult development requires about 28 or 8 days when temperatures average 60° and 82°F, respectively.

Twospotted mite feeding initially causes tiny, pale specks (stippling) on leaves. As feeding continues foliage can become pale green, yellowish, or whitish in large patches. Leaves may eventually turn brownish in large patches or overall and drop prematurely. On the underside of leaves where mites generally feed their pale cast skins and webbing may be visible, which also reduce crop aesthetic quality. Plants may grow slowly or remain undersized if heavily infested. Plants severely infested when young may die.

Biological and cultural controls and certain miticides (acaricides) are used to control spider mites.

Mite predators include bigeyed bugs, brown lacewings, green lacewings, larvae of predaceous midges, rove beetle adults and larvae, spider mite destroyer lady beetle, minute pirate bugs, and sixspotted thrips. Predatory mites are the most important biological control agents, commonly keeping spider mite populations low in outdoor crops. To conserve natural enemies, avoid the application of broad-spectrum, persistent insecticides and miticides and control ants and dust. See Relative Toxicities of Pesticides Used in Floriculture and Nurseries to Natural Enemies and Honey Bees to learn which pesticides are compatible with biological control.

Several species of predatory mites are commercially available for release. Phytoseiulus persimilis may be the most commonly used in greenhouses and nurseries. The best results have been obtained with periodic releases beginning early in the crop cycle when spider mite populations are low. Consider whether environmental conditions are favorable for the predators to be effective. For more information, see Biological Control and Releasing Natural Enemies for Biological Control of Agricultural Pests.

Carefully inspect new plants and propagation stock to ensure they are pest free. Rogue or effectively treat infested crop plants. Since spider mites feed on many different plants, keep production areas clean and free of weeds that can harbor infestations. Dispose of crop debris and weeds in covered containers .

Biological and cultural controls are organically acceptable management methods. The botanical neem oil, certain narrow-range oils (Organic JMS Stylet-Oil), and potassium salts of fatty acids (insecticidal soap) are acceptable for organic production.

Monitor crop plants regularly for mites and their feeding damage. Look for cast skins, foliage bleaching, silken fibers, and other changes in foliage appearance that are characteristic of mite feeding. At least weekly inspect the undersides of (especially lower) leaves with a 10X hand lens to detect mite presence. Sticky cards traps are not effective for monitoring these wingless pests.

Most miticides must be applied more than once to provide effective control. Follow label directions regarding reapplication times. And for guidelines on when to treat see Establishing Action Thresholds.

Selected Products Registered for Greenhouse or Nursery Ornamentals