Check houseplants for fungus gnats, says K-State horticulture expert

Domenghini also suggests scouting outdoor plants for scale insects

At a glance: Fungus gnats and scale insects are two pesky insects commonly found on plants this time of year. K-State horticulture expert Cynthia Domenghini outlines what to look for.

More information: Cynthia Domenghini, Cdom@ksu.edu

Feb. 6, 2025

By Pat Melgares, K-State Research and Extension news service

MANHATTAN, Kan. – If you’ve recently noticed tiny insects flying around your home or office, the cause may not be a ripe banana or leftover food.

Instead, says Kansas State University horticulture expert Cynthia Domenghini, the root of the problem may be houseplants.

“Fungus gnats are common household pests that are quite annoying,” said Domenghini, who offers the following tips for keeping them in check:

Water houseplants only as needed, rather than on a regular schedule, to avoid oversaturating plants and attracting the fungus gnats.
Dump water out of the saucer once it drains so that plants are not in standing water.
If fungus gnats are already present in your plants, allow the soil to dry at least through the upper three inches.
For extreme cases, repot the plant in fresh, soilless media. Remove as much soil as possible from the plant roots to eradicate the eggs and larvae of the gnats.

Scale Insects

Another pesky insect is often found in trees and shrubs around the home. Scale insects vary in size and host, and cause damage by sucking sap from plants.

“They can devastate crops of herbaceous ornamentals, as well,” said Domenghini, adding that the time to investigate plants for scale insects is now.

“Early detection of scale insects is the best way to prevent crop damage,” she said.

Many scale varieties have white, tan or brown shell-like coverings that are round or oval in shape. Domenghini said they can blend into the bark of herbaceous plants, so close inspection is necessary to detect them.

If signs of scale are found, Domenghini said a dormant oil can be used as long as the plant is in dormancy and the temperature is above 40 degrees Fahrenheit.

“Dormant oils are beneficial because they can combat a wide range of life stages for scale insects,” Domenghini said. “They are less detrimental to beneficial insects because of the application timing, and are less toxic than chemical controls.”

More information about dormant oils is available online from K-State’s Department of Entomology. Domenghini said information on specific scale varieties – including euonymus, magnolia, pine needle and San Jose scales – is available in publications available online from the K-State Research and Extension bookstore.

Domenghini and her colleagues in K-State’s Department of Horticulture and Natural Resources produce a weekly Horticulture Newsletter with tips for maintaining home landscapes and gardens.

Interested persons can subscribe to the newsletter, as well as send their garden and yard-related questions to hortsupport@ksu.edu, or contact your local K-State Research and Extension office.

***

KSRE logo
K‑State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well‑being of Kansans. Supported by county, state, federal and private funds, the program has county extension offices, experiment fields, area extension offices and regional research centers statewide. Its headquarters is on the K‑State campus in Manhattan. For more information, visit www.ksre.ksu.edu. K-State Research and Extension is an equal opportunity provider and employer.