Kill fungus gnats naturally with BTI

Fungus gnats live in moist potting soil, where they lay their eggs. But all-natural BTI will kill fungus gnats in their larval state--before they can become pesky, flying adults.


Looking for a way to kill fungus gnats naturally? Sooner or later you will have to deal with fungus gnats infesting your houseplants. Fungus gnats are the tiny flying pests that can swarm like an annoying black cloud whenever an infested houseplant or outdoor potted plant is moved.

Fungus gnats (Bradysia species) are small, mosquito-like insects that commonly infest the soil or growing medium of potted plants. When outdoor plants are brought indoors for the colder months, fungus gnats in the potting mix are brought indoors. That’s when they can quickly infest the soil of other houseplants.

Fungus gnats thrive in moist potting soil, where they lay their eggs. After the eggs hatch, fungus gnat larvae live in the top two to three inches of the potting soil. Fungus gnat larvae can cause plant damage by eating plant roots. After about two or three weeks, the fungus gnat larvae pupate in the potting soil. Then they become the tiny black adult gnats that fly erratically when a potted plant is moved.

Let the potting soil dry out between plant waterings. This will help control fungus gnats. But sometimes more aggressive measures are needed to kill these insect pests. Fortunately, there are now natural, non-chemical ways to naturally kill fungus gnats and control fungus gnat infestations.


Naturally kill fungus gnat larvae with BTI

To kill fungus gnats naturally, use BTI. Fungus gnats are closely related to mosquitoes, so fungus gnat larvae are effectively killed by BTI. (BTI is a naturally occurring bacterium that is deadly to mosquito larvae AND fungus gnat larvae.)

BTI, which is short for Bacillus thuringiensis israelensis, is deadly to mosquito larvae and fungus gnat larvae but harmless to other living things. The bacterium is nature’s way of keeping fungus gnat and mosquito populations down. But fortunately, BTI has no effect on other insects (such as bees and butterflies). Nor does it harm animals, fish, birds, plants, pets or people.

kill fungus gnats naturally with BTI
Mosquito Bits contains BTI to kill fungus gnat and mosquito larvae.

BTI is the active ingredient in top-selling Mosquito Bits®, which is approved for the control of fungus gnats. To kill fungus gnat larvae, simply shake the granular Mosquito Bits® onto the potting soil in houseplants. Also use it on other container-grown plants—including vegetables and herbs. Mosquito Bits® can also be mixed with potting soil prior to planting. When the plants are watered, the BTI in the Mosquito Bits® will be released. After subsequent watering, the BTI is washed below the soil surface. Fungus gnat larvae feed on the BTI and die. Buy Mosquito Bits here.

Because fungus gnats can be an ongoing problem, keep a container of Mosquito Bits on your Cypress Potting Table so you will remember to mix the Bits into the potting soil whenever you re-pot a plant. When the job of potting your indoor plants is done, take a break in your comfortable Victoria Rocking Chair.


Kill adult fungus gnats with horticultural oil

There is also an environmentally friendly, organic way to kill fungus gnats after they become adults. Summit® Year-Round® Spray Oil is a lightweight horticultural oil that controls a wide variety of insect pests including fungus gnats. Summit® Year-Round® Spray Oil is OMRI Listed® by the Organic Materials Review Institute and approved for use in certified organic production, and it’s perfect for indoor use.

Unlike many other pesticides that kill insects with toxic chemicals, Summit® Year-Round® Spray Oil literally smothers insects to death. The oil spray blocks an insect’s breathing holes (called spiracles), causing insects to die from asphyxiation.

Summit Year-Round Spray Oil is an organic way to kill insect pests

Summit Year Round Spray Oil can be used any time during the year to kill fungus gnats because it won’t harm tender plant buds, shoots or leaves. This lightweight oil has no odor, and it will effectively control pests on even sensitive plants such as tropical houseplants, roses, impatiens, citrus trees, and ferns. Summit® Year-Round® Spray Oil naturally kills fungus gnats. It also kills a wide variety of insect pests including aphids, whiteflies, spider mites, mealybugs, scale, thrips, lace bugs and more. Unlike chemical pesticides which can become less effective after repeated use, there is no known build-up of insect resistance to horticultural oil sprays.

Mosquito Bits® and Summit® Year-Round® Spray Oil are available at home centers, hardware stores, garden centers and at


Can BTI be used to control mosquitoes?

The short answer is Yes! In fact, BTI has been used to kill mosquitoes for more than 30 years. Bacillus thuringiensis israelensis (BTI) has been called “Mother Nature’s mosquito control” because this bacterium kills mosquito larvae and virtually nothing else. BTI also kills fungus gnats, because fungus gnats are genetically very closely related to mosquitoes.

Mosquito Dunks use chemical-free BTI to kill mosquitoes
Mosquito Dunks use chemical-free BTI to kill mosquitoes. Just float a Mosquito Dunk in standing water to kill mosquito larvae.

The best-selling BTI product in the world is called Mosquito Dunks. The handy donut-shaped Dunks can be placed in birdbaths, rainbarrels, ponds and anywhere that water collects. The BTI in the Mosquito Dunks will kill mosquito larvae for 30 days or longer. For more information, read Use BTI to Kill Mosquitoes. To check the price and availability of Mosquito Dunks, click here


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  1. Laura says

    I have a ton of fungus gnats in my yard and I think it’s because for two years I had a leak in my inground pool. I have a garden along the back of my house about 100 feet long by 3 feet wide. I do not have any plants, but there are rocks and dirt underneath. I’m thinking it’s drenched under there and that’s where they’re coming from. I noticed a ton of them there the other day, and they’re constantly by my patio door. We fixed the leak in the pool and I’m hoping to finally be rid of these pests. I’ve read solutions on how to get rid of them, but I’m looking for a solution where I don’t have to move the rocks and use something of the large area. Suggestions please, thank you.

    1. Randy Schultz says


      It does sound like your leaky in-ground pool created a wet breeding ground for fungus gnats. You need to buy Mosquito Bits (the large size!) and sprinkle them throughout the affected area. The BTI on the surface of the Mosquito Bits will kill the fungus gnat larvae in the soil. (BTI is a naturally occurring bacterium that kills the larvae of fungus gnats and mosquitoes but is harmless to people, pets, beneficial insects, birds and other wildlife.)

      With the infestation you describe, apply Mosquito Bits every 7 days throughout the summer. You should start seeing WAY FEWER fungus gnats soon! Click on the Mosquito Bits jug photo above and you will be taken straight to the Summit Responsible Solutions store on Amazon where you can buy Mosquito Bits.

      Randy Schultz

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