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Stop Fungus Gnats

Kill them at every stage

How to kill fungus gnats

Written by Mustafa Ayan Fact-checked against university extension/IPM sources Last reviewed: October 14, 2026

Direct answer

To kill fungus gnats, hit every life stage: trap adults with yellow sticky cards, kill larvae with a Bti product (Mosquito Bits or Gnatrol) or beneficial nematodes, and stop new eggs by letting the top of the soil dry between waterings. Killing only the adults won't end an infestation, because eggs, larvae, and pupae keep producing new ones.

Killing adults

Place yellow sticky cards flat on the soil or stake them upright just above it. Adults are attracted to yellow and get stuck before laying eggs. Cards also tell you how big the problem is and whether treatment is working. A fogger or aerosol spray may knock down flying adults temporarily, but it doesn't reach the stages in the soil.

Killing larvae

Larvae are where the infestation lives, and two options have the best support. Bti (Bacillus thuringiensis israelensis), sold as Mosquito Bits or Gnatrol, is a bacterium that is toxic to fly larvae and not to adults, plants, or most other organisms. Beneficial nematodes (Steinernema feltiae) are microscopic worms that hunt larvae in the soil.

A diluted hydrogen peroxide drench is a common home option, but guidance on it is mixed, so treat it as optional and cautious.

Killing eggs and stopping new ones

Eggs need consistently moist mix to hatch. Letting the top inch or two dry between waterings (as the plant tolerates) is the most effective way to cut them off. Bottom-watering and a layer of sand or grit on top help keep the surface dry.

The order that works

  1. Stop overwatering and let the surface dry.
  2. Put out sticky cards to catch adults and monitor.
  3. Apply Bti to every infested pot per the label, replacing a scheduled watering, not adding to it.
  4. Repeat per the product label and keep monitoring for at least two to three weeks after adults stop appearing.

What doesn't kill them well

Vinegar traps are built for fruit flies. Cinnamon and essential oils have little houseplant-specific evidence behind them. Sprays on the leaves don't reach larvae in the soil. See the natural-methods ratings for the honest breakdown.

Common questions

How do you kill fungus gnats fast?

Sticky cards cut adult numbers within days and Bti begins killing larvae soon after application, but total control takes weeks because eggs and pupae in the soil keep developing.

What kills fungus gnat larvae?

Bti (Mosquito Bits or Gnatrol) and beneficial nematodes (Steinernema feltiae) are the best-supported options, along with letting the soil dry. Hydrogen peroxide is an optional, less consistently supported choice.

Does rubbing alcohol kill fungus gnats?

Alcohol on adults may kill those it contacts, but it doesn't treat soil larvae and can harm plant tissue and roots, so it isn't recommended as a treatment.

Will fungus gnats go away on their own?

Only if you remove their breeding conditions. If the soil stays wet they keep cycling, so the population usually persists or grows.

Keep reading

Full guide: how to get rid of fungus gnats