Fungus Gnats in house plants pose no serious threat

Fun gnats are relatively harmless, but annoying. They lay their eggs on moist soil in house plants this time of year (winter). They larvae feed on roots, which is the only possible harm they can do other than annoy.

SPRINGFIELD, Mo. — Fungus gnats can be a nuisance in houseplants this time of year, says Kelly McGowan, horticulture educator with University of Missouri Extension, but no worries, mate.

“It happens this time of year because plants are not growing and not taking up much water from the soil. That means the soil often stays wet for a longer period of time, which is a perfect environment for fungus gnats to live and reproduce,” said McGowan.

Adult gnats do not fly well and normally stay close to the soil line of the plant. Gnats lay their eggs in the soil and the larvae hatch and feed on organisms in the soil

“Gnats won’t typically harm plants but heavy infestations of larvae can feed on plant roots,” said McGowan. “Adult gnats don’t bite humans and are more of a nuisance than anything else.”

Fungus gnats thrive in moist organic matter environments, such as rich, wet potting soil. For plants that can tolerate drier conditions, McGowan says to allow the soil to dry out between needed waterings.

“For plants that cannot tolerate dry conditions, repot with fresh potting soil,” said McGowan. “You can also treat the adults with insecticidal soap.”

For more information call 417-881-8909 or visit extension.missouri.edu.