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How to Deal with Fungus Gnats on Houseplants

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As people who adore plants, we never want to see them suffer at the hand of pests. But we especially don’t want to see pests in our houseplants because that brings the problem inside our homes—gross! Fungus gnats are nasty little winged critters that resemble tiny mosquitoes and are similar in size to fruit flies. The good news is that these plant flies are much less damaging than many other pests, and better yet, they’re pretty easy to get rid of.

 

What are Fungus Gnats?

Fungus gnats are identifiable by their long legs, transparent wings, and affinity for nutrient-rich, moist soils. You might notice these tiny flies buzzing around plant containers, but you won’t see them munching on the plant’s foliage directly, like some more harmful pests do. You will, however, notice them in the soil, feasting on plant roots and other organic matter including rotten fruit. Make no mistake—if left untreated, these bugs can still cause a considerable amount of damage.

Additionally, another pesky insect that can cause problems in moist environments is the drain fly. Similar in appearance to fruit flies, drain flies are small, fuzzy insects that thrive in damp and decaying organic matter, particularly in and around drains, sewage systems, and compost piles. They can become a nuisance indoors, especially in bathrooms and kitchens, where they lay their eggs in the gelatinous film found in drain pipes. If drain fly infestations are not addressed promptly, they can multiply rapidly and pose a significant annoyance to homeowners.

While adult fungus gnats only have a life span of about a week, they can make a pretty significant impact in that short period, laying up to 300 eggs in the right conditions. With this fast turnaround and short life cycle lasting just 3-4 weeks, populations can skyrocket pretty quickly. That’s why it’s crucial to take prompt action when you notice the signs of a fungus gnat infestation.

 

Signs of Fungus Gnats

If your plant has a fungus gnat problem, it’s pretty easy to identify. These plant flies aren’t actually great at flying, so they tend to stay pretty close to the plant. You’ll probably notice them whizzing about in zig-zag movements. Since they have such a quick reproduction rate, it’s common to see all the different stages of this pest at once. If you gently stir around the soil, you’ll likely see some bugs still in their larval stage. They have transparent bodies and black, shiny heads and live in the soil where they munch away on organic matter.

With winter upon us here in North Dakota, our plants are getting ready to settle in for the cold season. Unfortunately, that means it’s about time for these bothersome bug populations to peak. Dormant plants need less water during this time, meaning their soils stay wet longer. Wet soils, which encourage root rot and fungus, are a breeding ground for gnats. Be careful bringing your tender plants inside to overwinter, as you might be introducing your home to unwanted pests.

If left unnoticed and untreated, your plants will begin to show signs of stress. While fungus gnats don’t damage plant leaves directly, they munch on root hairs and diminish the soil of essential nutrients. This can lead to the sudden wilting and yellowing of plant leaves, weak growth, and an overall loss of vigor. To avoid the hassle of dealing with a full-blown gnat infestation, it’s essential to implement preventive measures and natural control methods.

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Natural Ways to Get Rid of Gnats

Natural control methods should always be your first step when dealing with any pest. While chemicals are sometimes a necessary second line of defense, natural and organic solutions are usually the least harmful and disruptive to your plant and home. Luckily, most populations of fungus gnats can be prevented and eradicated naturally if they’re identified and treated in time.

Make sugar and dish soap traps: One effective natural control method for dealing with fungus gnats involves creating a simple homemade trap using a tablespoon of sugar. By mixing a tablespoon of sugar with a few drops of dish soap in a small container and filling it with water, you can attract and trap these pesky insects. The sugar acts as bait, luring the gnats into the solution, and the dish soap breaks the surface tension of the water, causing the gnats to drown when they attempt to land on it. Placing these traps near affected plants can help reduce the fungus gnat population without resorting to chemical solutions, providing a safer and environmentally-friendly approach to pest control.

Avoid overwatering: Allow the top few inches of soil to dry out before watering your houseplants. Not only will this prevent fungus gnats from choosing your plant as their ideal new home, but it will also disrupt their reproductive cycle and help to lessen populations that have already moved in. Remember that different plants have different watering needs, so understanding your plant’s specific requirements is crucial.

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Use sticky traps: They’re not just for mice! Sticky traps are simple solutions to a lot of pest problems. Place them directly on the surface of the soil, and you’ll catch gnats that are on the move. Remove them from the trap or dispose of and replace the trap often (every 2-3 days) to intercept their egg-laying. Yellow traps are especially efficient at attracting these insects. Additionally, you can make your own sticky traps using bright yellow paper coated with a sticky substance.

Make cider and vinegar traps: Similar to how you might trap fruit flies, mix equal parts of cider and vinegar in a shallow dish or can. Place the trap near the affected plant or even on the soil surface inside the container. The pests will be attracted to the mixture but will drown after they land in it. For added effect, add a drop of dish soap to break the surface tension and make it easier for the gnats to sink into the liquid.

 

How to Kill Fungus Gnats in Houseplants

Introduce beneficial nematodes: Adding more bugs to the mix might sound counterproductive, but it’s a straightforward solution to controlling pest populations. Nematodes are teeny-tiny worm-like bugs, often so small that you can’t even see them with your naked eye. They work to penetrate fungus gnats and other insects in their larval stage, releasing bacteria that end up consuming the pest from the inside out. It’s grim and gross when you think about it, but not as gross as letting gnats kill your precious houseplants!

Mosquito dunks and Hydrogen Peroxide: These small, donut-shaped products contain a bacteria called Bacillus thuringiensis israelensis (BTI), which is toxic to the gnat larvae but safe for plants, pets, and humans. Place a mosquito dunk in your plant’s water tray or dissolve a piece of it in water and use the solution to water your plants. The BTI will target and kill the gnat larvae present in the soil. Alternatively, you can use hydrogen peroxide as a quick and effective way to get rid of larvae by mixing four parts water with one part hydrogen peroxide and soaking your soil with the solution. The hydrogen peroxide will help kill the gnat larvae and any eggs in the soil without harming your plant.

 

How to Get Rid of Fungus Gnats in Houseplants

When all else fails, there are always insecticidal products and sprays available to control pest populations. There are plenty of products that target either the larval stage or the adult stage, but either is fine. As long as you effectively target one stage of their life cycle and reapply frequently, you should be able to eradicate these nasty plant flies in just a few weeks.

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Hydrogen peroxide is a quick and effective way to get rid of larvae, killing them on contact. Mix four parts water with one part hydrogen peroxide and soak your soil with the solution. Neem oil can also be diluted with water and applied to the soil to kill larvae. You can also use neem oil as a spray to kill adult flies on contact. Finally, pyrethrin sprays contain extracts that are toxic to many pests and can kill fungus gnat larvae and flies on contact.

For hydrogen peroxide, mix one part 3% hydrogen peroxide with four parts water. Carefully pour this solution onto the top of the soil, ensuring it reaches the root zone. The hydrogen peroxide will help kill the gnat larvae and any eggs in the soil without harming your plant.

Neem oil is a natural insecticide derived from the neem tree. Dilute neem oil according to the manufacturer’s instructions and apply it to the soil. The oil will work to suffocate the larvae and disrupt the life cycle of the fungus gnats.

Pyrethrin sprays are made from the extracts of certain chrysanthemum flowers. Spray the product directly onto the soil, and it will kill both the larvae and adult gnats on contact.

Remember to read and follow the instructions on any commercial product you use to ensure it’s safe for your specific houseplant and application.

Although fungus gnats may seem like a minor annoyance, they can quickly become a significant problem if left unchecked. Thankfully, there are several natural and effective ways to deal with them, allowing you to maintain healthy and thriving indoor plants. By implementing preventive measures like avoiding overwatering and using sticky traps, you can reduce the likelihood of a gnat infestation. If the problem persists, turning to natural remedies like beneficial nematodes, vinegar traps, and dealing with gnat infestations in sink drains can help control the population without resorting to harsh chemicals.

Regularly inspect your plants for signs of infestation and act promptly if you notice any. By taking these simple steps and incorporating natural control methods, you can ensure your indoor plants stay free from these pesky flying pests and continue to bring joy and beauty to your home throughout the year.