Plants suffering from an infestation of fungus gnats may show signs of wilting and yellowing of the leaves. The larvae may also cause damage to the roots.
Fungus gnats are small dark flies that mostly affect the soil of houseplants. The adults are non-biting and harmless but annoying as they tend to fly up when watering the plants.
These pests are destructive at the larval stage . They feed primarily on fungi and organic matter, as well as roots. Below is a picture of the larvae and eggs.
How to Get Rid of Fungus Gnats Naturally
These are some of the most common home remedies and natural control methods for eliminating the critters.
1. Sticky Traps (Yellow)
The critters infest soil. As a result, position the traps on the soil surface to catch the adults before they lay eggs, thereby disrupting the life cycle.
These mosquito-like insects are particularly attracted to yellow, so it’s easy to catch them on these yellow sticky traps.
You can also hang the traps vertically close to plants or in nurseries and indoors to catch new adults flying in.
2. Diatomaceous Earth
This non-toxic white dusty substance is a natural insecticide that comes from the fossilized remains of tiny aquatic creatures.
The minute glass-like shards of diatomaceous earth will cut through the larvae and adult pests, dehydrating and killing them.
Mix it in with potting soil or sprinkle it onto the top layer of the soil.
3. Apple Cider Vinegar
You can use apple cider vinegar to control fruit flies as well as adult gnats.
Fill small jars with ACV and a little liquid soap. Seal the jar then poke holes in the top big enough for the Fungus flies to enter.
Next, place the jars near your plants. The critters love the stuff. As a result, they’ll fall in and drown.
Refresh as soon as the gnats die. Continue this home remedy until the infestation is under control.
4. Bacillus thuringiensis israelensis (Bti)
This is a bacterium naturally occurring in the soil. BTi produces a protein that is toxic to the larvae once ingested.
Following the product instructions, water the soil with the solution to kill the larvae. The product also works on mosquito larvae.
5. Beneficial Nematodes
Purchase these microscopic roundworms and work them into the soil where they will hunt down and parasitize fungus gnats larvae.
Beneficial Nematodes produce bacteria that destroy the larvae from the inside out. Remaining nematodes will thrive and reproduce from the nutrients in their prey and survive in the soil to limit any new gnat infestations.
Purchase them online or at various organic farm store centers.
6. Potato Slices
A rather unpleasant but easy and inexpensive way of controlling fungus gnats by removing the larvae.
Cut one-inch slices of raw potato and layer them on the soil surface where they should attract larvae. After a few hours, you will find the larvae underneath the slices.
Look for clear to white tiny grub-looking creatures. Remove the top layer of the soil, larvae, and potatoes. Repeat until free of the problem.
7. Hydrogen Peroxide
The value of this common household chemical is that it kills fungus gnat larvae on contact. Moreover, it can eliminate the pest at all stages of its life cycle – eggs and adults too.
Leave the soil to dry out a little then dilute 3% strength hydrogen peroxide to four parts water. Next, thoroughly soak the soil around the plants with the solution.
Additionally, lightly spray the leaves and stems of plants. This DIY gnat spray should not harm the plants.
This works differently from other fungus gnat home remedies by destroying the fungus that these creatures need to thrive.
Spread a thick layer of cinnamon powder over the soil and repeat every few weeks. However, true Ceylon cinnamon is most effective for this purpose.
Soil gnats like damp soils. As a result, a layer of sand on the soil surface will dry out fast, helping to thwart egg-hatching. It will also discourage the critters from laying more eggs.
10. Soapy Water
To eliminate gnat larvae this is a simple method with a product usually already in the home.
A solution of one tablespoon of organic liquid soap to a quart of water can fix the problem. Spray the soapy water solution on plants and soil.
Repeat once or twice to ensure all larvae are killed.
11. Keep Soil Dry
The first line of attack against these pests is to isolate the plants to stop the infestation from spreading.
They are very much surface creatures so allow the top level of the soil to dry out to deter adults from egg-laying.
Preventing the soil from getting excess moisture is always helpful in controlling these indoor pests.
This commercial product is a botanical pesticide formulated that contains Azadirachtin.
Molt-X works by preventing insect molting and inhibiting feeding. It also acts as a pest repellent, effectively avoiding future infestations.
Apply this treatment as a foliar spray and also use it to drench the soil.
Azera is another organic insecticide containing Azadirachtin from Neem. It also contains Pyrethrins derived from chrysanthemum flowers.
These 2 ingredients are powerful botanical pesticides that help control a wide variety of insect pests including garden gnats.
Apply a spray solution as per the product directions onto the plant and on the soil.
14. Bug Buster-O
Monterey Bug Buster-O is a commercial, quick knock-down organic spray. Dilute according to the product instructions and spray at the first sign of plant gnats.
Direct this killer spray straight at the adults in flight and also around the plants and seedlings to kill others and destroy the larvae.
However, exercise caution to avoid spraying outdoors near bees as the product is toxic to these important pollinators.
15. Melissa Oil
This is also known as lemon balm oil and is very attractive to these critters, as well as other insect pests.
A few drops of Melissa Oil added to sticky traps will invite a cloud of adult flies to your trap. Remove this homemade fungus gnat trap and set a new one frequently, adding some oil each time.
16. Earth Juice goGnats
Earth Juice goGnats is effective against many flying and soft-bodied pests. It also has a pleasant aroma.
Use it as a foliar spray or soil drench. Moreover, it is great for indoor and outdoor use.
17. Neem Oil
Neem oil is a powerful organic solution to controlling most garden pests. However, the best choice is to purchase cold-pressed neem oil.
Combine one tablespoon of the oil with one teaspoon of organic liquid soap in a liter of warm water. Shake well.
Next, drench the soil and spray the plants with the solution. Repeat as necessary.
Four plants are particularly susceptible to attack by fungus gnats: geraniums, African violets, poinsettias, and carnations. However, many indoor/greenhouse plants are also vulnerable.
The most important action to keep these pests at bay is to keep the soil dry to slow down or stop an infestation. Additionally, adding one or more of the above natural methods will help eliminate the problem.