Eliminating Fungus Gnats: Treatment Options

By: HowStuffWorks.com Contributors  | 
A gnat on a white background.
Fungus gnats wreak havoc by feeding on fungi, decaying plant matter, plant roots, and leaves. Debbie Maize / Getty Images / Dorling Kindersley

You take the time to water your plants, fertilize them, and ensure that they get as much natural light as your space allows. But all it takes is a few weeks of overwatering to cultivate hundreds of unwanted visitors. Don't stress! There are countless fungus gnats treatment options that are cheap and effective.


What Are Fungus Gnats?

Fungus gnats are about one-eighth of an inch long and are dark grey or black with thin wings, long legs and long antennae. Although they have a very short life span, they wreak havoc by feeding on algae, fungi and decaying plant matter, as well as plant roots and leaves.

They don't fly very far and tend to cluster around the plant that they are infesting. Fungus gnats thrive in the late fall and winter, hovering around indoor plants. Read here for some ideas of how to get rid of this nuisance.


Fungus Gnat Life Cycle

They don't live long, but that doesn't stop a whole family of them from infesting your favorite potted plants and invading your personal space. From egg to adult, they only live an average of 3 to 4 weeks, most of which is spent in or on the soil surface [source: Planet Natural Research Center]. But, in their short life, adult gnats can lay as many as 300 eggs, which is why fungus gnat infestations can become so problematic.

The eggs hatch in as little as four days, though the larval stage is much longer. The larvae feed on and live in moist soil for roughly 12 days before graduating to the pupal stage, which lasts another for to six days [source: Hernandez]. Adult fungus gnats grow to be as big as a quarter of an inch, and spend around eight days flying around the houseplant the birthed them laying eggs.


Treating a Fungus Gnat Infestation

Make sure the flies you see are really fungus gnats by trying the raw potato test. Place a piece of raw potato on the soil near an infested a plant. If these are fungus gnats, you will see them migrating to the potato within a few hours. If you lift the piece of potato, you should see the larvae.

  • Insecticide: Drench the soil with microbial insecticide, such as bacillus thuringiensis, more commonly called Bt. This is the most effective way to kill any fungus gnat larvae.
  • Sticky traps: Place yellow sticky traps near the infested plant. These 3-by-5-inch (7.6-by-12.7-centimeter) adhesive-based traps attract and kill many, though not all. fungus gnats.
  • DIY liquid traps: Fill a small bowl with warm water, apple cider vinegar, sugar, and a few drops of liquid dish soap to create a trap to attract and kill fungus gnats.
  • Diatomaceous earth: Diatomaceous earth is organic matter sourced from the fossilized skeletons of aquatic organisms known as diatoms. Fungus gnats also hate the stuff, which is why sprinkling it around the base of an infected plant can work so well.


How to Prevent Fungus Gnats

Fungus gnats aren't harmful to humans, but they can wreak havoc on your houseplants. They aren't the best roommates in the world either. Which is it's always best to prioritize fungus gnat prevention wherever possible.

Fortunately, it's not that hard to prevent fungus gnats from invading your beloved house plants. Try the following prevention methods to keep your home gnat free:


  • Avoid overwatering: The leading culprit of plan-related fungus gnat infestation is overwatering. These pests thrive in moist potting soil, and you can control fungus gnats by letting the soil dry out a bit between waterings.
  • Sand: Covering the base of your plants with a half-inch of sand has been shown to stop fungus gnats in their tracks too. Not only can it help kill a current infestation, but it can also prevent fungus gnats from returning.
  • Keep your drain clean: Fungus gnats can breed in your sink drain too. That can be prevented by clearing it of any organic debris, and keeping it clean.

Enjoy Pest-Free Plants Today!

You pay good money for your house plants, and put a lot of work into keeping them healthy and green. Though they don't pose a health risk to humans or pets, they have been shown to stunt plant growth and contribute to root rot [source: University of California Agriculture & Natural Resources].

Don't let these easy-to-eliminate annoyances take out your indoor greenery. Fight back, apply a few of the tips above, and say goodbye to fungus gnats for good.