Fungus gnats are tiny black flies about 1/8 inch long that can emerge in huge swarms in garden beds. While they seem harmless, these pests can damage your plants. Fungus gnat larvae feed on roots and facilitate the spread of fungal diseases. Left uncontrolled they may stunt or kill seedlings and reduce the yields of established plants.
If your raised beds or containers are crawling with small flies, chances are you have a fungus gnat infestation. Here are tips to identify, prevent, and safely eliminate these annoying insects in your garden.
Recognizing Fungus Gnats
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Adults look like mosquitoes with long legs, transparent wings and dark bulbous eyes. They are weak fliers.
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Larvae are thin, whitish maggots up to 1/4 inch long found burrowing in soil.
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Plants may appear stunted or wilt easily due to damaged roots.
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You may find trails of tiny flies swarming over soil. Large populations can emerge, especially after watering.
Where Fungus Gnats Come From
Fungus gnats are attracted to damp, organic-rich soils to breed. Potential sources of infestations include:
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Overwatered pots and beds
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Poorly draining or compacted soil
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Excessive mulch in decomposition
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Dead plants, leaves, and debris
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Active compost piles
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Manure and compost added to garden
Female gnats lay eggs in moist soil or organic matter. The larvae feed and eventually pupate in soil before emerging as adults to repeat the cycle.
Preventing Fungus Gnats in Garden Beds
Prevention is the best way to avoid severe fungus gnat issues:
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Allow soil to dry out between waterings. Check moisture before watering.
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Improve drainage by adding sand, gravel, or perlite to soil.
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Eliminate weeds and garden debris where gnats may breed.
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Turn compost piles regularly to kill larvae. Keep compost bins away from garden.
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Apply thin layer of sand or diatomaceous earth to deter egg-laying.
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Use sterile seed starting mix and clean containers for seedlings.
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Cover seedlings with floating row cover fabric to exclude gnats.
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Use yellow sticky traps around beds to catch adult gnats.
Treating Existing Fungus Gnat Problems
If you already have an active fungus gnat infestation, here are organic methods to eliminate them:
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Remove excess moisture by allowing beds to dry out before watering again. Improve drainage.
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Eliminate garden debris, rotted produce, and wet mulch where larvae live.
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Apply beneficial nematodes to soil to kill larvae. Brands like NemAttack work well.
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Use yellow sticky traps around beds to catch adults. Move them to fresh areas every few weeks.
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Sprinkle diatomaceous earth or fine sand on soil to kill larvae through desiccation. Reapply after rain or watering.
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Use a high-pressure stream of water to dislodge larvae from soil.
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Apply Bacillus thuringiensis (Bt) bacteria to kill larvae without harming plants.
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Re-pot severely infested plants in fresh sterile mix to fully eliminate gnats.
Tackling Fungus Gnats Organically
It’s best to avoid using chemical pesticides which may also kill beneficial insects like bees. Here are some organic approaches to try:
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Drench soil with a solution of 1 part hydrogen peroxide to 4 parts water to kill larvae.
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Water in mosquito dunks which contain Bacillus thuringiensis bacteria deadly to fungus gnat larvae but not plants or people.
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Spray plants with neem oil extract, insecticidal soap, or spinosad-based products, avoiding blooms where bees forage.
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Introduce natural predators like ladybugs, lacewings, and predatory mites that consume both larvae and adults.
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Amend soil with diatomaceous earth, crushed eggshells, sharp sand, or gravel to abrade and kill larvae.
Be Vigilant to Prevent Reinfestations
Fungus gnats can go through several generations and life cycles per season. Keep monitoring beds after treatment and promptly apply controls again at the first sign of rebound. Combining multiple organic methods provides the best control and prevents gnats from building resistance.
With persistence and patience, you can eliminate fungus gnats from your garden beds and enjoy pest-free plants. The key is taking quick action at the initial signs of infestation before it gets out of hand. Pay close attention while watering and working beds to spot any sudden swarms of small flies hovering over soil. Addressing them immediately using organic methods will nip problems in the bud.
Fungus Gnats as Disease Vectors
Fusus gnats do hurt plants, but it’s important to get rid of the larvae and adults because they can spread disease. Those recovering from fungus gnat problems still face the risk of infections. Fungus gnat larvae can get to your plant’s roots and spread fungus spores that adult gnats drop there. This could lead to a number of common plant diseases. The most commonly transferred diseases include black root rot, Pythium blight, Verticillium wilt, Botrytis blight, and Fusarium wilt.
As a safety measure, use a copper fungicide on any plants that are hurt and those that are nearby a day or two after using a pesticide. This makes sure that even if your plant came into contact with disease-causing fungi spores, it won’t get the disease. A root drench is more effective than spraying the plant’s foliage, as that’s where damage would be done.
So, fungus gnats have been eating your African violets. Let’s talk about how to get rid of both adult flies and their young. We suggest that you use an integrated pest management plan to protect all of your plants and people who live in your greenhouse for good.
Organic Fungus Gnat Control
Interestingly, one of the best things I know to use to get rid of these pests is something you probably already have at home. Hydrogen peroxide (the standard 3% topical variety) can be used as a soil drench.
One part peroxide to four parts water should be mixed together and poured through the root zone soil until it starts to come out of the pot’s bottom. The peroxide kills fungus gnat larvae on contact.
Neem oil is also an effective soil soak to combat fungus gnat larvae. Follow the manufacturer’s instructions and mix the oil with water. Then, soak the soil right where the plant’s roots are. You can also spray the upper portion of the plant to keep adult gnats at bay.
Concentrated azadirachtin naturally occurs in neem oil. It’s safe in hydroponic use as well as in greenhouses, gardens, and indoors. Use it per the manufacturer’s directions in the same way you would use neem oil.
Pyrethrin sprays are also effective against fungus gnats and their larvae. To use pyrethrins, lightly mist all plant surfaces and the top of the soil. You don’t want the plants dripping wet, a thin mist will be enough. If there are fungus gnat larvae in the soil, spray the area where the adults usually rest to make the top layer very wet. Be careful not to water too much. Let the soil dry to at least a 2″ depth. Reapply these in three to four weeks until the problem has subsided and the insects are gone.
A predatory mite of the Hypoaspis miles species preys upon adults and larvae. It also gets rid of thrips and springtails, which are annoying bugs that can be found in the garden or greenhouse. These are best employed outdoors or in greenhouses as single specimens are harder to treat.
You can get rid of fungus gnats with a lot of different biological control agents, as you can see. Apply insecticides in conjunction with good cultural practices and prevention methods and you’re set!.
Foolproof Fungus Gnat Prevention and Control
FAQ
Are fungus gnats bad for vegetable garden?
How do you get rid of fungus gnats in your garden?
How to get rid of gnats in a raised garden bed?
How do you get rid of fungus gnats in vegetables?
What are fungus gnats?
If you live in a temperate or tropical area, you’ve most likely seen insect pests called fungus gnats before. They’re small flies that infest soil potting soil, any container media, and other organically decomposed sources and materials. Fungus gnat larvae feed on fungi and plant roots in soil and organic matter.
Do fungus gnats like dry soil?
Use a chopstick to carefully poke into the medium, moving it around a little to create air pockets and allow water to penetrate deeply but drain easily. Repot every one to two years, as overly decayed soil can become compacted. Okay, so now you know that fungus gnats love damp soil. Dry soil would prevent infestations, but our plants do need water.
How do I get rid of fungus gnats?
Here are some of the common treatments that didn’t solve my fungus gnat problem. Fungus gnats seem to prefer moist soil, so by bottom watering, you’re keeping that top layer dry while giving your plants the hydration they need.
Do fungus gnats damage plants?
While adult fungus gnats don’t directly harm garden plants, their larvae can be destructive. They feed on plant roots, causing root damage and making the plants more susceptible to diseases. Plant root damage: Fungus gnat larvae feed on the fine hairs of plant roots, stunting plant growth and leading to wilting or yellowing leaves.
What causes fungus gnats on houseplants?
Well, fungus gnats are the kinds of insects that are almost always around to some degree, but there are certain things that can cause them to take over your plant’s soil. When it comes to houseplants, the absolute number one cause of fungus gnats is overwatering (or lack of drainage, which is basically the same thing).
Are fungus gnats attracted to indoor plants?
Fungus gnats are attracted to a variety of indoor plants, particularly those that require moist soil conditions, such as: These plants are not necessarily more susceptible to fungus gnat infestations, but their growing conditions may make them more attractive to the gnats.