Updated: Mar 26, 2022
What are Fungus Gnats?
Fungus gnats are small black flying bugs, somewhere between a fruit fly and a small mosquito in size. Some may mistake fungus gnats for fruit flies, but whereas fruit flies are generally found around your food, fungus gnats are found on the surface of the soil or around your plants.
What do Fungus Gnats do to Plants?
While it is lovely to have a house bursting with plants, having a house bursting with fungus gnats is not! Unfortunately these pesky little bugs are a common problem on indoor plants. While the mature fungus gnats do not bite or harm plants they can be annoying and unpleasant to have in your home. Fungus gnat larvae on the other hand live in the top inch of your plant's soil and feed on the tender roots, causing harm to your plants. Young plants are especially vulnerable to fungus gnat damage because they have not yet developed a strong root support system.
The good news is there are a number of ways to get rid of fungus gnats! Choose a few of these methods to try. A multi-pronged approach will be most effective!
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How to Get Rid of Fungus Gnats
1. Sticky Paper for Fungus Gnats
Sticky paper meant for catching flies and bugs gives you a quick and easy start to controlling and managing mature fungus gnats. Keep in mind you will still need to treat the gnat larvae in the soil. I like to cut 1 in. x 1.5 in. pieces of sticky paper and lay them on top of the soil in my house plants. That way I can keep an eye out for any fungus gnat infestations and know what plants are affected. I purchased this 50 sheet pack of sticky paper from Amazon. I think I will have enough to last me years!
2. Hydrogen Peroxide for Fungus Gnats
Hydrogen peroxide can be used to treat fungus gnat eggs and larvae by diluting 1 part hydrogen peroxide with 4 parts water and allowing this to soak the top 2 inches of your plants. Hydrogen Peroxide works best to treat fungus gnats if you use this teatment when the soil is on the dry side. You may hear the peroxide fizzing, this is normal. Fungus gnats develop from egg to an adult gnat in 3 to 4 weeks. You will want to repeat the peroxide treatment once a week for 4 consecutive weeks to ensure any new eggs that may have been laid during the treatment process are destroyed.
3. Bottom Water Your Plants to Discourage Fungus Gnats
Fungus gnats thrive on warm, moist soil. Water your house plants from the bottom for the duration of your fungus gnat infestation. Set plants in a pan of water and allow them to soak up water from the bottom, keeping the top two inches of the soil dry, rather than pouring water on the surface of the soil. This works well with larger plants but does not work when you are growing seedlings that may only be planted in two inches of soil to begin with. Keep watering to a minimum, and keep plants on the dry side for the duration of your fungus gnat infestation.
4. Using Cinnamon to Deter Fungus Gnats
Cinnamon is a natural insect repellant. It is relatively inexpensive to buy. Sprinkle a layer of cinnamon on the surface of your plant soil to discourage fungus gnats. (As an added benefit, cinnamon may also help prevent mold or fungus from forming on the surface of constantly moist soil of seedlings! This may help prevent damping off.)
5. Using Diatomaceous Earth for Fungus Gnats
Diatomaceous earth, or DE for short, is made from fossilized remains from aquatic organisms. Its small edges are abrasive to insects, cutting into their exoskeleton and killing them. DE works only when dry. Take special care not to inhale as it can be damaging to lung tissue. To use diatomaceous earth for fungus gnats, sprinkle it on the dry surface of your plants and keep the surface of the soil dry by only bottom watering your plants for 4 consecutive weeks.
6. Using Neem Oil for Fungus Gnats
Neem oil can be used to treat fungus gnats by spraying thoroughly on plants and soil every 4 days for 4 consecutive weeks. Keep in mind when using neem oil for fungus gnats that although it works well to treat the pupae and mature gnats, it doesn't kill the fungus gnat eggs and larvae beneath the surface of the soil.
7. Essential Oil Spray for Fungus Gnats
I have made this essential oil spray using Young Living Thieves cleaner along with a few other oils and have had success treating a variety of plant pests. Use the recipe below and spray plants and soil every 4 days for 4 consecutive weeks. The key here is consistency.
8. Using Sand to Deter Fungus Gnats
Fungus gnats like easy access to soil. Cover the surface of the soil with 1/4 inch layer of sand to prevent fungus gnats from burrowing into the soil to lay eggs.
9. Using Nematodes for Fungus Gnat Control
Nematodes are a natural fungus gnat predator. Nematodes are live microbial organisms that feed off fungus gnats. You can order nematodes online or purchase them at garden centers. Once the fungus gnat larva are gone (the food source for the nematodes) the nematodes will die and become a harmless part of your plant's soil. Nematodes can be a very effective organic treatment for fungus gnats.
If using the pot poppers pictured below, cut open the bag and sprinkle the little balls on top of your plant's soil. Keep in mind, these organisms are live and should not be shipped in freezing temperatures.
10. Mosquito Dunks for Fungus Gnats
Mosquito dunks are another effective option for fungus gnat control. Mosquito dunks contain a naturally occurring bacterium called Bacillus thuringiensis subspecies israelensis (or B.t.i.). This bacterium is not harmful to fish, birds or other animals.
The best way to use mosquito dunks to control fugus gnats is to leave one of the round dunks in your watering can. The bacteria is released into the water and kills the fungus gnat larvae.
Fungus Gnat Control
Fungus gnats can be so persistent and can be quite difficult to completely get rid of. One female can lay up to 200 eggs! As far as what treatments you choose, I would suggest for sure trying to go easy on the watering and allowing your plants to stay on the dry side then choosing a spray or a soil treatment and staying very consistent with it for the 4 week life-cycle duration of a fungus gnat.
Plants with high moisture content inside the stem (such as aloe vera and succulents) can host fungus gnats up inside the plant where they are nearly impossible to treat. It may be worthwhile to toss those plants.
Fungus gnats can lay dormant in plants or in soil for extended periods of time. This is why, just when you think you may have won the battle, more seem to appear.
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