When houseplants are infested it may mean they are overwatered. Fungus gnats do not survive if the soil becomes dry so one management option is to permit the soil to dry out to the extent tolerable between waterings. Otherwise, houseplant insecticide spray can be applied to the surface of the soil and around the edges of the pot. As a last resort, a solution of malathion insecticide can be applied to the soil surface as a soil-drench treatment in place of a regular watering. This must be done after taking the plant outdoors.
Additional pesticides are available to commercial growers.
Iowa State University , Ames, Iowa. This information subject to a usage policy .