Two-Spotted Spider Mites

Two-spotted spider mites can kill off many of your garden plants as temperatures rise and humidity drops. Before a hot, dry summer kicks in, it’s a good idea to know what to look for.

Two female two-spotted spider mites with egg (Giles San Martin) CC BY-SA 2.0

Two-spotted spider mites (Tetranychus urticae) can become a serious threat to your citrus and other fruit trees, most vegetables, and many ornamentals, such as marigolds, roses, and salvia. Beans, blackberries, blueberries, cucumber, eggplant, lettuce, peas, squash, strawberries, and tomatoes are all favorite foods of the two-spotted spider mite.

Two-spotted spider mite description

As arachnids, all mites have two body segments and eight legs. Two-spotted spider mite eggs are round to spherical, but very difficult to see. Instead, you may see the webbing used to protect those eggs. Colorless larvae, which start out with only six legs, go through two developmental stages to reach greenish-yellow, eight-legged adulthood. This transformation can occur in as little as 5 days, and females can lay 120 eggs in their lifetime, so populations can rapidly explode.

An interesting note, unfertilized eggs hatch into males, while fertilized eggs hatch as females. This is called arrhenotoky.

Males are smaller and have narrower bodies and are more active than females. These close cousins to red mites are greenish-yellow to brown, with two dark spots, and they even have a red winter phase, but you probably won’t be able to see them without a hand lens. [Those dark spots are accumulated body wastes, so they are not always visible.] At only 1/50” long, two-spotted spider mites are easier to find by looking at the damage they cause.

​Damage caused by two-spotted spider mites

As sap-sucking pests, similar to citrus mealybugs and citrus bud mites, these mites pierce plant cells and remove the contents. Hidden from view by feeding on the underside of leaves, they often go unnoticed until the damage becomes obvious. Mite feeding causes stippling and bleaching. These damaged areas increase, causing bronzing and early leaf drop. If you look at the underside of these leaves, you will often see the cast-off exoskeletons of mites. You may also see extensive webbing over buds, stems and flowers. Extensive feeding can cause stunting and even plant death.

How to manage two-spotted spider mites

Since two-spotted spider mites feed on such a wide range of plants, they are difficult to control. Mites favor feeding on stressed plants, so proper feeding and irrigation can help your plants seem less appealing to these pests. In addition, you can use these tips to reduce problems caused by two-spotted spider mites:

• reduce nearby weeds, which may serve as hosts
• place new plants in quarantine until you are certain that they are pest-free
• inspect the underside of leaves regularly with a 10X hand lens
• monitor for signs of mite feeding

​Predatory mites, such as Phytoseiulus persimilis, ladybugs, minute pirate bugs, and lacewings are all beneficial insects that feed on two-spotted spider mites, so keep you yard hospitable to these helpful predators. Mites are developing resistance to most chemical pesticides, but insecticidal soaps are effective against mites, with horticultural oils (not dormant oils) coming in a close second. These treatments are only affective against the mites that come into contact with it, so repeat treatments are often necessary.