Modify your watering practices. Allow the houseplant’s soil surface to completely dry out. Withhold water as long as you can without causing injury to the plant. Fungus gnats require a moist environment, so the larvae will die when the soil dries out.
Pour one-quarter to one-half inch of apple cider vinegar into a clear or semi-opaque plastic cup, creating an effective fungus gnat trap. Add a drop or two of liquid dish soap and stir to combine thoroughly. Cover the top of the cup with transparent tape, leaving a one-eighth-inch opening in the center of the taped area.
The presence of fungus gnats, or fruit flies, hovering in and near your houseplant is annoying. Adults are harmless to houseplants unlike their larvae, which can cause severe root system damage. Often drawn by unrefrigerated ripening fruit or even beer and fruit juice containers stored in recycle bins, these tiny flies seek the intoxicating essence of fermentation and are also attracted by damp areas such as household drains. Fungus gnats are particularly fond of depositing young in moist potting soil to feed upon fungi and decaying plant matter. However, instead of throwing the plant out, you can get rid of pesky fungus gnats using household vinegar.
Place the vinegar trap near your houseplant and check it daily. Don’t disturb it if you see gnats congregating on top of the taped area; they’ll soon find their way into the hole and down to the vinegar.
Set up some yellow sticky traps around your houseplant to attract hovering adults to the area.
How to Use Vinegar to Get Rid of Fungus Gnats on a House Plant
Take the houseplant out of its pot gently if you have discovered fungus gnat larvae. Remove as much soil as you can without disturbing its roots. Seal the infected soil up in a plastic bag and discard it; do not add it to the compost heap. Clean and disinfect the plant container. Repot the plant in a good commercial sterilized potting soil mix.
Cut a fresh raw potato into chunks. Place a few pieces on the houseplant’s soil for two or three days. Pick up the potato pieces and look to see if anything has been chewing on them.
Remove debris and dead plant material from the soil surface daily to eliminate an adult fungus gnat attractant and larval food source.
Plants that are overwatered are susceptible to fungus gnats and their larvae can damage roots, but fortunately, vinegar works well in attracting the annoying pest.
In small numbers, fungus gnats are more of an annoyance than anything. In fact, the adult gnats don’t actively harm plants nor people. If their population gets out of hand, however, the larvae may start feeding on plant roots, causing notable damage. This is especially bad for young plants, such as seedlings, which have only a few delicate roots. Fungus gnats are also capable of spreading the plant pathogen that causes damping off and the eventual death of seedlings.
- To make a cider-vinegar trap: Find a shallow container—a tuna can is perfect—and fill it with equal parts water and apple cider vinegar. (The liquid should be at least ¼-inch deep.) Put a few drops of liquid dish soap into the mixture and stir gently. Place the trap near the base of the affected plant or, ideally, inside the pot on top of the soil. Check it every few days to refresh with new vinegar and water.
Fungus gnats are completely harmless to humans, since they can’t bite and don’t spread diseases. They can be a problem for houseplants, however, when their population explodes and their larvae starts to feed on plants’ roots. Fungus gnats may also spread Pythium, a group of plant pathogens that causes “damping off” in seedlings.
Mosquito dunks (with beneficial bacteria): Mosquito dunks are used to keep mosquito larvae from populating fountains, animal troughs, fish ponds, and other small bodies of water. The product consists of a dry pellet containing a type of bacteria called Bacillus thuringiensis subspecies isrealensis. This beneficial bacteria infects and kills the larvae of flying insects, including mosquitoes, fruit flies, and fungus gnats.
Once you have a fungus gnat infestation, using consistent management and prevention techniques is key to ending it. Further down on this page, we’ve listed a few of the best ways to both get rid of adult gnats and prevent new gnats from emerging.
Appearance: Adult fungus gnats are a grayish-black color and have gray or see-through wings. Their long legs and long antennae give them a mosquito-like appearance, though they are much, much smaller in size. Compared to a fruit fly, fungus gnats have a thinner body with longer legs and antennae.
Larvae have a small, black head and a thin, white or see-through body.
Keep soil dry: Fungus gnats seek out moist soil, so allowing your houseplants to dry out a bit between waterings can slow down or stop an infestation. Let the top inch or two of soil dry out before watering again, and try to go as long as possible between waterings. Gnats may be deterred from laying their eggs if the soil is dry on the surface.
Sticky cards traps: These traps consist of a yellow note card covered in a sticky adhesive. They are most effective when cut into small squares and placed directly on top of the soil or attached to skewers just above the soil. Adult gnats will fly or crawl onto the card and become trapped. Fungus gnats are attracted to the color yellow, so use the yellow sticky cards rather than the blue ones. Both can be bought at most hardware or garden stores, as well as online.
Cider-vinegar traps: Simple and effective, cider-vinegar traps consist of a shallow container with a small amount of apple cider vinegar, water, and liquid dish soap.
Identify, control, and get rid of fungus gnats in your plants with these tips from The Old Farmer's Almanac.