Fungus Gnats on Houseplants: How to Identify, Treat, and Prevent Them
Fungus gnats are tiny, flying insects that thrive in damp soil. While they don’t directly harm plants as adults, their larvae feed on organic matter and delicate root hairs, which can weaken seedlings, stunt growth, and make plants more vulnerable to disease. Indoors, they’re one of the most frustrating pests for plant lovers because they seem to appear out of nowhere and multiply quickly.
Identification & Lifecycle
Life stages: Egg → larva → pupa → adult.
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Eggs: Laid in clusters in the top layer of moist soil.
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Larvae: Tiny, translucent worms with black heads. These are the most destructive stage, feeding on decaying matter and root hairs.
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Pupae: Develop in the soil before emerging as flying adults.
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Adults: Small flies that hover around soil and fly up when plants are disturbed.
Damage symptoms: Wilting or yellowing leaves, slowed growth, weak seedlings, and in severe cases, plant decline due to damaged roots.
Ecology & Spread
Fungus gnats are, unfortunately, almost unavoidable for plant lovers. They’re opportunistic little insects that show up wherever the environment suits them—and if they find moist, organic-rich soil, they’ll happily move in. Infestations often start with something as simple as overwatered houseplants, a bag of contaminated potting mix, or even a new plant brought inside, or even a plant that just likes more consistent moisture. Once indoors, the consistent warmth and humidity create the perfect breeding ground, which is why fungus gnats can feel like a never-ending nuisance once they’ve made themselves at home.
Pests Are Normal—Don’t Panic
If you’ve spotted fungus gnats in your home, you’re not alone. They’re one of the most common houseplant pests and aren’t a sign you’ve failed your plants. The key is reducing soil moisture, targeting larvae in the soil, and managing adult populations before they reproduce.
Biological Control with Koppert Solutions
Koppert offers proven biocontrol options that target fungus gnats effectively:
Nematodes
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Entonem (Steinernema feltiae): Microscopic roundworms that attack and kill fungus gnat larvae in the soil. Highly effective and safe for plants.
Predatory Mites
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Hypoaspis (Stratiolaelaps scimitus): Soil-dwelling mites that feed on fungus gnat larvae and other soil pests.
Beneficial Bacteria
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Vectobac (Bacillus thuringiensis israelensis): Targets fungus gnat larvae by disrupting their digestive system.
Sticky Traps
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Safers Sticky Traps: Catch adult gnats, reducing breeding and making infestations easier to monitor.
Other Effective Treatments You Can Use
Alongside beneficials, these accessible retail treatments work well for houseplants:
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How it works: Fine powder that dehydrates larvae in the soil.
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How to use: Sprinkle a thin layer on top of soil between waterings.
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How it works: Disrupts soft-bodied pests, including larvae near the surface.
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How to use: Apply directly to soil and foliage to reduce populations.
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How it works: Lure and trap adults, cutting down breeding cycles.
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How to use: Place near infested plants to monitor and reduce flying gnats.
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How it works: Provides quick knockdown of flying adult gnats.
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How to use: Spray around affected plants to reduce populations fast.
Using Beneficials with Other Treatments
To maximize success, consider how treatments interact:
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Beneficials first: Release nematodes, predatory mites, or bacteria before using insecticidal soaps or sprays.
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Avoid overlap: Sprays can kill beneficials if applied at the same time.
Integrated Pest Management (IPM) for Fungus Gnats
An effective IPM plan includes:
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Apply nematodes or predatory mites to target larvae. (if you use another treatment remember that will kill your beneficials too so I recommend choosing one method at a time)
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Use diatomaceous earth for added soil protection.
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Place sticky traps to monitor and reduce adult populations.
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Use sprays like Dr. Doom or insecticidal soap for quick knockdown.
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Adjust watering habits—allow the top 1–2 inches of soil to dry between waterings or bottom water.
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Isolate new plants and use clean soil to prevent reinfestation.
Frequently Asked Questions
Are fungus gnats harmful to people or pets?
No—they’re a nuisance but not harmful to humans or pets.
Why do they keep coming back?
Because moist soil provides the perfect breeding ground. Consistent watering adjustments plus treatment is key.
Can I get rid of them without chemicals?
Yes—biological controls, diatomaceous earth, and sticky traps are highly effective when combined.
Conclusion
Fungus gnats may be annoying, but they’re very manageable with the right approach. By combining biological controls, sticky traps, soil treatments, and improved watering practices, you can break their lifecycle and protect your plants.
At Urbane Eight, we carry trusted Koppert biocontrols along with effective retail-ready products like Diatomaceous Earth, Safer’s Insecticidal Soap, Sticky Traps, and Dr. Doom Plant Spray.
Shop Urbane Eight today for fungus gnat solutions and keep your houseplants thriving pest-free.