Fight spider mites on houseplants

By Dawn Pettinelli - UConn Home & Garden Education Center
Featured Article - posted Mon., Jan. 9, 2012
Photo by Leanne Pundt, of UConn. - Contributed Photo

One quite common houseplant pest that I just noticed on those lovely variegated ivies I am overwintering is the spider mite. Mites have four pairs of legs, so they are not true insects, but are placed in a separate group of creatures called arachnids. Spiders are also included in this group.

Spider mites feed by piercing the leaf or flower bud and removing the liquid contents of the plant’s cells. Since this destroys the chloroplasts, which give plants their green color, the affected areas appear stippled or speckled, with irregular silver or yellowish spots.

Two-spotted spider mites are the species most commonly encountered on houseplants. They are very tiny - only 1/25 to 1/50 of an inch long - and are difficult to see without the aid of a hand lens. These mites, comparable in size to a grain of pepper, usually have two distinct dark spots on their back, hence the name.

Most often you will notice your plant’s leaves looking off-color and rather yellowish, and where high populations of spider mites have developed, fine webbing will be visible between the leaves and stems. Mites generally feed on the undersides of the leaves, making them less likely to be discovered until considerable damage has occurred.

Eggs of the two-spotted spider mite are laid at the base of the plants, as well as on the leaves or buds. Populations can build up very rapidly. At temperatures of 75 degrees F, it only takes five days for eggs to develop into adults, whereas 40 days are required for development at temperatures around 50 degrees F. As you might suspect, plants located closest to a heat source are where infestations can develop most rapidly.

Spider mites can be controlled by repeated washings with cold water. Bring plants to the kitchen sink or bathtub and spray with as much force as the plants can tolerate. Since mites are not insects, most common houseplant insecticides will not satisfactorily control them. Miticides formulated for indoor use are sometimes available, but often quite toxic, and cold water treatments work just about as well for small, localized infestations. Spider mites abhor cool, moist conditions, so after washing, move your plants to a cooler location. Keep an eye on them and wash them with cold water if you notice any signs of reinfestations.

African violets, cyclamens, geraniums, gloxinias and New Guinea impatiens, among others, are often bothered by another species of mite, the cyclamen mite. Leaves and flowers appear stunted, deformed and knobby. Cyclamen mites are smaller in size than spider mites and are very difficult to control.

Consider discarding plants infested with cyclamen mites. Even harsh chemical controls are not always effective. One remedy that has been suggested is to immerse plants in 110 degree F water for 15 to 30 minutes. To be on the safe side, space remaining plants so the leaves do not touch. Wash your hands thoroughly with soap before touching healthy plants.

Always quarantine new houseplants before placing them among healthy plants. As with many aspects of gardening, preventative measures can save you a lot of time, effort and expense. If you have questions about controlling mites or on other gardening quandaries, call, toll-free, 877-486-6271, visit the website at or contact your local Cooperative Extension Center.

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