The two-spotted spider mite, Tetranychus urticae , is one of the most common and widely distributed spider mites in the United States. These mites prefer the hot, dry weather of the summer and fall months, but may occur anytime during the year. Overwintering females hibernate in ground litter or under the bark of trees or shrubs.
Spider mites spin fine strands of webbing on host plants. David Cappaert, Michigan State University, Bugwood.org
The two-spotted spider mite is a general feeder that attacks a wide variety of plants including shade trees, shrubs, and flowers. Like all mites, two-spotted spider mites have needle-like, piercing-sucking mouthparts. Because of their small size and habit of feeding on the underside of foliage, this species may go undetected until a population has caused serious damage to a plant. This species is known by several other common names such as “red spider mite” or “glasshouse spider mite.”
They are more commonly found on perennials than woody plants, but they have a particular fondness for roses.
If you’ve counted the legs, you know that once these mites grow out of their larvae stage, they do have four pairs of legs. That’s one similarity to their namesake. But that’s not the only thing spider mites have in common with the arachnids. All spider mites spin fine strands of webbing on their host plant, hence the name.
The guide Follow these tips to keep spider mites away from your nursery.
Scout them out: Scout for spider mites in the winter or spring on plants that have damage from the previous year. Look for eggs at the base of needles, on the underside of leaves, and in bark crevices using a hand lens. During the growing season, beat foliage against a white sheet of paper. Dislodged mites will appear as small, dark spots moving around on the paper. Predators such as phytoseiid mites, minute pirate bugs, or green lacewing larvae may also appear on the paper.
Treatment time: Mites reproduce very quickly so if you find a few this week, it could mean you could find thousands by next week. By the time mite damage appears on plants, mites have been present for a while. Even if mites are no longer present, prior mite damage may worsen late in the season as leaves experience heat or drought stress.
Shake it off: Two-spotted spider mites possess the ability to develop resistance to miticides within a short period of time. A number of spider mite populations have already developed resistance to commonly used miticides (such as abamectin) due to extensive use over the years.
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The facts about Two-spotted spider mite T. urticae adultAppearance: Nymphs, adult males, and reproductive adult females are oval-shaped, yellow or greenish. There are one or more dark spots on each side of their bodies, and the top of the abdomen is free of spots. Larvae resemble their parents, but are smaller and have only three pairs of legs. Adults and nymphs have four pairs of legs.
T. urticae with eggs on phloxEggs: Two-spotted spider mite eggs are about 1/180 inch (0.14 mm) in diameter and are laid on the undersides of leaves. They are spherical, clear, and colorless when laid but become pearly white as hatch approaches.
Two-spotted spider mites with eggs Life Cycle: The adult female lives two to four weeks and is capable of laying several hundred eggs during her life. Adult female two-spotted spider mites may stop reproduction during the coldest winter months in production areas of warmer climates, like California. Hot dry weather favors the development of severe infestations of this pest. Depending on weather conditions, a complete generation of this pest may be completed in 7-20 days. The various generations overlap and all stages can be found on most host plants during the summer months.Spider mite infestation
Prevention: Protect the mites’ natural enemies as much as possible by choosing insecticides and miticides that are least harmful to beneficials. If necessary, supplement natural enemies by releasing predatory mites. The use of biological control will only be effective in regulating two-spotted spider mite populations if the predatory mites are released prior to mite populations becoming established.
Predator mites commercially available for release:
Phytoseiulus persimilis Neoseiulus (Amblyseius) californicus Neoseiulus fallacis P. persimilis is used most frequently in spider mite suppression. It is an aggressive feeder, multiplies and spreads rapidly, and is a specialist predator that feeds exclusively on pest mites. In the absence of these pest mites, P. persimilis feeds on its own species, causing the population to gradually disappear.
Spider mites leave webbing behind Treatment: Two-spotted spider mites have a history of rapidly developing resistance to miticides when a miticide is repeatedly applied to the same population.
Alternating miticides that have different modes of action may reduce development of resistance to a specific miticide. Avoid unnecessary spraying and treat only infested portions of the field. Organophosphate, carbamate, and pyrethroid insecticide applications can induce two-spotted spider mite outbreaks. If possible, avoid early season insecticide applications or apply insecticides that are less disruptive to beneficial arthropods. Careful selection and use of insecticides early in the season can potentially reduce the number of miticide applications. Sources: UC-Davis IPM, University of Florida, Penn State University Extension
Photos by: Eugene E. Nelson, Bugwood.org, Bruce Watt, University of Maine, Bugwood.org, David Cappaert, Michigan State University, Whitney Cranshaw, Colorado State University, Bugwood.org, Louis Tedders, USDA Agricultural Research Service, Bugwood.org