An infestation of fungus gnats can cause plants to show signs of wilting, slow growth, and yellowing of the leaves.
Fungus gnats are small dark flies that mostly affect indoor houseplants. The adults are non-biting and do not cause damage to plants; however, they can be annoying as they tend to fly up when watering houseplants.
These pests are destructive at the larval stage [1]. The larvae feed primarily on fungi and decaying plant material, as well as plant roots. Below is a picture of fungus gnat eggs in soil and a larva.
How to Get Rid of Fungus Gnats Naturally
These are some of the most common home remedies and natural control methods for controlling the critters.
1. Sticky Traps (Yellow)
The critters infest soil. Therefore, position the traps on the soil surface to catch the adults before they lay eggs, thereby disrupting the fungus gnat 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
A great natural pesticide for getting rid of fungus gnats in the house, 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 [2]. BTi produces a protein that is toxic to gnat worms, mosquitoes, and certain other pests once ingested.
Following the product instructions, water the soil with the solution to kill fungus gnat larvae. You can also use it to get rid of mosquito larvae.
5. Beneficial Nematodes
Purchase beneficial nematodes and work them into the soil where they will hunt down and parasitize fungus gnats larvae in the soil.
They produce bacteria that destroy the larvae from the inside out. 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 is by removing the larvae.
Cut one-inch slices of raw potato and layer them on the soil surface where they should attract gnat larvae. After a few hours, you will find the larvae underneath the slices.
Look for whitish-to-clear worms with shiny black heads. 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 gnats larvae on contact. Moreover, it can eliminate the pest at all stages of its life cycle – eggs and adults too.
To use hydrogen peroxide for fungus gnats, dilute one part hydrogen peroxide (3%) with four parts water. Leave the soil to dry out a little then use the solution to water your plants.
Also, lightly spray the leaves and stems of plants. This DIY gnat spray will not harm your plants.
8. Cinnamon
This works differently from other fungus gnat home remedies by destroying the fungus that these creatures need to thrive.
To use cinnamon for fungus gnats, spread a thick layer of the powder over the soil and repeat every few weeks.
9. Sand
Soil gnats like damp soils in order to lay their eggs. As a result, a layer of sand on the soil surface will dry it out fast. This discourages them from laying eggs there.
10. Soapy Water
Make a homemade spray for fungus gnats by combining one tablespoon of liquid soap with a quart of water.
Spray this soapy water solution on plants and soil. Repeat once or twice to ensure all larvae in the soil are killed.
11. Keep Soil Dry
One of the first lines of attack against these pests is to create an inhospitable environment so they lack what they need to thrive.
Therefore, keep the top level of the soil dry to deter adults from laying eggs. Preventing the soil from getting excess moisture is always helpful in controlling these indoor pests.
12. Molt-X
This commercial product is a botanical pesticide that contains Azadirachtin.
Molt-X works by preventing insect molting and inhibiting feeding. It also acts as a pest repellent.
Apply this treatment as a foliar spray to kill fungus gnats. You can also use it to drench the soil.
13. Azera
Azera is another organic insecticide containing Azadirachtin from neem seeds. It also contains Pyrethrins derived from some chrysanthemum flowers.
These 2 ingredients act as powerful botanical pesticides that help control a wide variety of pests including garden gnats. Apply as 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 insecticide for fungus gnats and other pests. Dilute according to the product instructions and spray at the first sign of plant gnats.
Direct this killer spray straight at the adult gnats 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. It 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 this fungus gnats treatment as a foliar spray and soil drench. Moreover, it is great for indoor and outdoor use.
17. Neem Oil
Neem oil is a powerful organic solution used to control many garden pests.
To use neem oil fungus gnats, combine one teaspoon of organic liquid soap with one tablespoon of neem oil and a liter of warm water. Shake well.
Finally, drench the soil and spray your plants with the solution. Repeat as necessary.
Takeaway
Plants particularly susceptible to attack by fungus gnats include 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 remedies will help eliminate the problem.
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