January 12, 2005 | By: Aimee Heald-Nielson

Wet and cold winter weather puts outdoor gardening on hold for a few months. However, a University of Kentucky entomologist believes Kentuckians can enjoy indoor houseplants with relatively few pest problems.

“Fortunately, unlike gardening outdoors, there are a small number of insect pests that routinely attack houseplants,” said Ric Bessin, UK College of Agriculture entomologist. “One common group of pests that occasionally thrive in houseplant potting soil is fungus gnats.”

Bessin said high humidity and moist, organic growing media in homes and greenhouses provides an excellent breeding ground for several types of gnats. These gnats also are abundant outdoors where they can breed in virtually any accumulation of standing water that remains in place for several days.

“Fungus gnat larvae can be serious pests of some indoor houseplants,” he said. “The larvae of most species are scavengers, feeding on decaying organic matter in soil. However, larvae of some species will feed on root hairs, enter the roots or even attack the crown or stem of the plant.”

Bessin said fungus gnat larvae injury causes root wounds and can encourage root rot. Plants infested with fungus gnats generally lack vigor and may begin to wilt. Adult gnats frequently are seen running on the foliage and potting soil before injury to the plant becomes apparent. Besides injuring the plants, the adult gnats also can become a nuisance in other areas of the home, he said. 

It takes larvae about 14 days to mature under the soil. Adults live only about a week. Indoors it takes about three weeks to complete a generation. 

Bessin said the key to fungus gnat control is water management in houseplants.

“The larvae must have constantly wet media,” he said. “Watering houseplants less often, so that the media dries some between waterings, will serve to break the life cycle of these tiny pests. Fungus gnats usually don’t require insecticide for control.”


Writer: Aimee D. Nielson 859-257-4736, ext. 267
Contact: Ric Bessin 859-257-7456