|K-State Research and Extension Horticulture Newsletter
Fungus gnats are small insects (1/8 to 1/10 inch long) that are common in high-organic-matter houseplant soils that are kept moist. Though adults are mosquito-like in appearance, they do not bother humans or pets. It is actually the larvae or maggots that can injure plants by feeding on the roots. Symptoms include sudden wilting, loss of vigor, poor growth and yellowing leaves. Use of sterile media and avoiding overwatering your houseplants can help prevent infestations. Existing infestations can be controlled Bacillus thuringiensis v. israelensis which is sold under the names of Gnatrol and Knock-Out Gnats. (Ward Upham)
Cynthia Domenghini runs the Horticulture Response Center in the Department of Horticulture and Natural Resources at Kansas State University. Other contributors include K-State Extension Specialists.