How to Kill Gnats on Indoor Plants

Fungus gnats and fruit flies feed on decaying plant materials, such as the fallen leaves and dead surface roots in houseplant soil. The pests breed quickly once they find a suitable feeding ground. Though the gnats rarely affect the health of the houseplant, they are an unattractive pest and a nuisance inside the home. Controlling the gnats requires destroying the young within the plant's soil and eliminating the adults before they lay more eggs in the houseplant pot.

Things You'll Need

• Diatomaceous earth
• Insecticide

Instructions

1. Water houseplants when the top 2 inches of soil feels dry. The eggs of the gnats cannot survive in soils that don't remain wet.

2. Remove dead plant matter, such as fallen leaves, from the soil surface. Gnats feed on dead and decaying leaves, roots and flowers.

3. Sprinkle diatomaceous earth, available from garden centers, on the soil surface in the houseplant pot. Diatomaceous earth kills gnat maggots and larvae.

4. Treat the plant with a insecticide containing pyrethroid, following the package application instructions. Pyrethroid insecticides target adult gnats.

Tips & Warnings

• Placing sticky fly trap near the houseplants may eliminate minor infestations.

• Insecticides do not kill the maggots or larvae in the soil, only adult gnats.

References

• Colorado State University Extension; Fungus Gnats as Houseplant and Indoor Pests; W.S. Cransaw, et al.; April 2009
• University of Nebraska Extension; Fungus Gnats; Don Janssen; January 2005