Andre CampbellLarge numbers of fungus gnat larvae can damage seedlings, young plants, and weak houseplants. The larvae mostly eat fungi and decaying plant material in moist soil, but they may also feed on plant roots when populations are high.
Fungus gnats are small, mosquito-like flies that are common around houseplants, seedlings, greenhouses, and other plants growing in damp soil.
Adult fungus gnats mainly annoy, while the larvae can damage plants [1].
How to Get Rid of Fungus Gnats Naturally
Below are some of the most common home remedies and natural control methods for controlling these pests.
1. Sticky Traps
Fungus gnats lay their eggs in the soil. Sticky traps help catch adult fungus gnats and reduce the number of adults that can lay eggs. They also help you monitor the infestation.
Adult fungus gnats are often attracted to yellow, so yellow sticky traps can help catch them. You can also hang the traps near plants in nurseries or indoors to trap new adult gnats flying in.
2. Diatomaceous Earth
Food-grade diatomaceous earth may help control fungus gnat larvae and other small insects.
It works best when it is dry. Water makes it less effective at damaging insects’ bodies.
Sprinkle a thin layer over the soil surface and reapply after watering, if needed. Allow the soil surface to dry before reapplying.
3. Vinegar
You can use vinegar to help control fruit flies and adult gnats.
Pour some apple cider or white vinegar into a shallow bowl and add a little liquid dish soap. Next, place the bowl near the affected plant.
Some fungus gnats may be attracted to vinegar traps, but these traps often work better for fruit flies than for fungus gnats.
This method may catch some adult fungus gnats, but it should not be relied on as the main treatment. It primarily targets flying adult gnats rather than soil larvae.
4. Bacillus thuringiensis israelensis (Bti)
Bti is a bacterium that naturally occurs in soil [2]. When fungus gnat larvae eat Bti, the bacteria produce toxins that damage their digestive systems and kill them.
If the product label lists fungus gnat larvae, follow the instructions and apply it to the soil as directed. Some Bti products can also be used to control mosquito larvae.
5. Beneficial Nematodes
You can also purchase beneficial nematodes and apply them. Certain beneficial nematodes, such as Steinernema feltiae, attack and kill fungus gnat larvae in the soil.
They work best when the soil stays moist enough for them to move around.
6. Raw Potato
Raw potato pieces may attract fungus gnat larvae. This can help you check whether larvae are present in the soil and remove some of them.
Slice raw potatoes into chunks and place them on the soil surface. Fungus gnat larvae may gather under the potato pieces, making them easier to remove.
After a few days, remove the potato pieces and throw them away. Repeat the process with fresh potato pieces if needed.
7. Hydrogen Peroxide
A diluted solution made from 3% hydrogen peroxide may help kill some fungus gnat larvae in the soil. However, using it too often or in a strong concentration may damage plant roots.
Mix one part hydrogen peroxide (3%) with four parts water. Let the soil dry a little, then use the solution to water your plants.
Some gardeners use this solution occasionally, but it may harm plant roots and helpful soil organisms if used too often.
Test the solution on one plant first, and do not use it regularly as a replacement for proper watering practices.
8. Cinnamon
Cinnamon is sometimes recommended as a home remedy because it may have antifungal properties. However, it is not a reliable way to control a fungus gnat infestation.
Drying the soil and using Bti, sticky traps, or beneficial nematodes are more reliable options.
9. Sand
A thin layer of coarse sand can make the soil surface less suitable for adult fungus gnats to lay eggs. However, it will not solve an infestation by itself.
Use coarse sand rather than fine sand, which may hold moisture.
10. Soapy Water
Insecticidal soap may kill adult fungus gnats on contact.
If using a homemade soap solution, test it on a small part of the plant first. Avoid strong dishwashing detergents, which may damage leaves.
Spray directly on adult fungus gnats when possible, but remember this only affects adults and will not kill larvae in the soil.
11. Keep the Soil Dry
One way to fight these pests is to make the soil less suitable for them. This way, they won’t have what they need to survive.
Allow the top layer of soil to dry between waterings when the plant can safely tolerate it. Do not let plants that need constantly moist soil dry out too much.
Check the soil with your finger before watering. If the top layer is still damp, wait a little longer before watering again.
However, do not allow plants to become severely dry, as stressed plants may become weaker and more vulnerable.
12. Molt-X
Molt-X is a botanical pesticide containing azadirachtin. Azadirachtin can affect insect feeding and growth.
Check the product label to make sure fungus gnats are listed before using it.
13. Azera Gardening
This product is another organic insecticide containing azadirachtin from neem seeds.
It also contains pyrethrins, which come from certain chrysanthemum flowers. The two active ingredients work in different ways to control a range of insect pests.
Use Azera Gardening only according to its current product label. The label tells you which pests it controls and how to apply the product.
14. Bug Buster-O
Monterey Bug Buster-O is an organic insecticide that helps control fungus gnats and other pests. Dilute and apply it according to the product label.
Follow the product label carefully. Avoid spraying flowers when bees and other pollinators are actively visiting them.
15. Bottom Watering
Bottom watering can help reduce fungus gnat infestations by keeping the top layer of soil drier. Since adult fungus gnats prefer moist soil for laying eggs, this method makes the environment less favorable for them.
To bottom water, place the plant pot in a shallow tray of water for about 15 to 30 minutes. Doing so allows the soil to absorb moisture through the drainage holes.
Remove the pot afterward and let the excess water drain away. Bottom watering can help reduce fungus gnats when combined with other methods.
16. Organocide
Organocide is a 3-in-1 spray that helps control several insect pests, including fungus gnats. It is suitable for both indoor and outdoor use.
Check the label before use because product registrations can change.
17. Neem Oil
Neem oil is a plant-based product that can help control some garden pests.
To use neem oil to control fungus gnats, mix it according to the product label. Some neem oil products are ready to use, while others must be diluted before application.
Apply the neem oil according to the product label. Some products may be used as a soil drench, while others are meant to be sprayed on plants.
Fungus Gnat Prevention Tips:
- Avoid overwatering.
- Use well-draining soil.
- Ensure pots have drainage holes.
- Use sterile potting soil when starting seeds.
- Do not leave water standing in saucers or trays.
- Remove dead leaves and other decaying material from the soil surface.
- Keep new plants away from your other plants for a short time. Check them for fungus gnats before placing them nearby.
Takeaway
Fungus gnats, also called sciarid flies, are small flies that live around moist soil. Their larvae feed mainly on fungi and decaying organic matter, but large numbers may also damage plant roots.
They can affect many houseplants, seedlings, greenhouse plants, and other plants growing in wet soil.
Allowing the top layer of soil to dry between waterings is one of the most effective ways to help prevent fungus gnat problems.
Combining methods can help control an infestation. For example, allow the soil to dry when the plant can tolerate it, use yellow sticky traps to catch adults, and use Bti or beneficial nematodes to target larvae.
Sasha Campbell
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