Houseplant gnats, or fungus gnats, do not typically cause much damage to plants but are an annoyance in the home. Use a combination of home remedies or cultural changes to remove fungus gnats if you do not wish to use insecticides, and isolate the infested plant to prevent infestation in your other plants.
Excess soil moisture creates conditions for fungi development, which attracts fungus gnats and provides a suitable environment for their larvae. By reducing the amount of moisture in the soil, you create less favorable conditions for the fungus gnats. Colorado State University Extension recommends that you allow the soil's surface to dry between each watering.
A change of the plant's potting soil can aid control of fungus gnat larvae, as they live within the soil. Use sterilized potting soil, as recommended by the University of Minnesota Extension, because garden soil may contain additional pests. A layer of charcoal and coarse gravel at the bottom of the pot will improve soil drainage for moisture control, according to Oregon State University.
Sticky flytraps catch adult fungus gnats, and you can purchase these or make your own. Coat yellow cardboard with petroleum jelly, as suggested by Colorado State University Extension, and set or hang the cardboard pieces near the plant. Other tacky substances will suffice if you do not have petroleum jelly.
Prune and Clean Foliage
Decaying plant parts provide food to fungus gnats, so cut them away from the plant and discard them. Dust may attract plant pests, too, according to the University of Minnesota Extension, but a burst of water will remove this and temporarily jolt adult flies from the foliage.
Neem oil controls fungus gnat larvae in the soil and is a plant-derived substance. Consider this for an organic alternative to typical pesticides if cultural control does not eliminate the infestation.