Are you worried you have fruit flies? But they don’t look quite right? Well, you don’t have fruit flies.
You have these creatures called fungus gnats (Sciaridae).
Fungus gnats can’t harm humans. There are no diseases they can pass on to you. There’s nothing they can do to hurt you. Except fly in circles in front of your face and annoy you.
They’re like any other gnat you’ve encountered.
But they can pass diseases onto your indoor plants. And fungus gnat larvae feed on the roots of your plant.
The roots are the most vulnerable area and should be protected at all costs. These pests can be the worst when you’re not expecting it.
Once an infestation grows, all heck breaks loose. Between the gnats themselves and the diseases they bring, it all spells trouble.
Are you ready to get rid of these annoying pests already?
Now that you’ve identified your little (or big) bug problem, it’s time to get down to it.
This guide has everything you need. We discuss the basics of fungus gnats. Then it’s time to get serious. We go over how to prevent and get rid of these gnats.
What are Fungus Gnats?
Fungus gnats are often mistaken for fruit flies. This is due to their fly behavior and that they’re the same size.
It’s also because many people are unaware of fungus gnats and what they can do to indoor plants.
They come from several families including:
All these families belong to the superfamily Sciaroidea.
Adult fungus gnats are small but not so small you can’t see them. An adult gnat ranges between 1/16th to 1/8th of an inch in length.
The adult is a grayish or blackish color. Their wings are a translucent gray. This is why they’re nicknamed “dark-wings”.
The gnats have long skinny legs and a long segmented antenna. Their antennas are what distinguish them from other flies and gnats.
Fungus gnat larvae grow between 1/8th and 1/4th of an inch. The larvae have a clear body. They have dark heads. Their heads are small and hard to see.
They live two to three inches beneath the potting soil of a plant.
When the larvae change, they change into pupae. Pupae are white but as they get older, they get darker in color.
The pupae stage evolves into the adult gnat stage.
Fungus gnats love moisture and humidity. You find them flying or walking on the soil of your plant. You find the larvae in the soil.
Most fungus gnats can take the cold, unlike a lot of other bugs. This is because the gnats have antifreeze proteins.
Antifreeze proteins are a type of polypeptides. Some animals and bugs have this protein so they can take freezing weather.
How Fungus Gnats Reproduce
Male and female adult fungus gnats reproduce together so the female can lay eggs.
The female gnat lays about 200 eggs in their lifetime. They lay the yellow eggs on organic matter toward the surface of a plant’s potting soil.
Three days after the female lays eggs, they hatch into larvae. For this to be possible, the temperature range needs to be around 75F.
Larvae are the immature form of an insect when they’re between an egg, pupae, and adulthood.
Once the eggs hatch, the larvae burrow into the potting soil. They feed on any fungi and decaying parts of your plant.
They also feed on the hair on the roots as well as the roots themselves.
Two weeks after the larvae emerge from eggs, they go through a metamorphosis process. This process changes them into pupae.
Pupae exist between three and four days. Then they turn into adult fungus gnats and leave the soil.
Adult fungus gnats only live for a little over a week. Their only purpose is to produce more gnats.
Fungus gnats produce an entire generation between a mere 15 and 18 days. They have several overlapping generations in a year.
The higher the temperature, the faster the reproduction and life cycle moves forward.
How Fungus Gnats Attack Your Plant
Fungus gnats love the moisture from the potting soil of a plant. But the adult gnats don’t harm plants.
It’s their larvae that you need to worry about. And when an infestation grows, the more eggs are being laid and the more larvae are forming.
When larvae burrow into the soil, they find the roots of your plant. They also love to feed on the tissue of the lower stem on your plant.
Young plants (or seedlings) are the plants that are at the highest risk from fungus gnats. Seedlings aren’t developed, making them vulnerable.
Fungus gnats can also spread the horrible plant disease referred to as “Pythium”. A Pythium blight terrorizes your plant.
The quick spread of Pythium is the scariest part of having fungus gnats.
The disease causes root rot and often leads to the death of your plant.
Root rot is any deterioration of the roots. Sometimes due to heavy moisture and sometimes due to disease.
You want to heal the roots before they get too bad if your plant has root rot. Treating roots is an easy process.
You remove your plant from the soil so you expose the roots. Wash away all the soil from the roots as well as any of the damaged roots.
You have to remove any of the affected roots that didn’t come off while washing. Shears work best.
Dip the shears in isopropyl alcohol to prevent the disease from spreading.
Before you put your plant back, you need to replace the potting soil and clean the pot.
How to Prevent Fungus Gnats
Preventing fungus gnats is the best way to go. They can be hard to get rid of once an infestation gets too large.
Keep in mind, fungus gnats are all over the United States. They can be a problem for almost anyone with an indoor plant.
Always, always check any new plants you bring into your home. Since larvae hide under the potting soil, you’ll have to do more than a quick look over to be sure.
If you’re concerned, you can put your new plant in a different room for two weeks. You can watch the plant to see if any fungus gnats pop up.
Another way to prevent fungus gnats from infesting your plant is to make sure air is circulating. You especially want circulation around the soil.
You can accomplish this with a blowing fan.
Air circulation keeps the top layer of the soil dry. They’re less likely to come check out your plant, let alone lay any eggs if it’s dry.
Not to mention, the gnats have a hard time flying when a fan is blowing at them.
It’s also important not to over-water your plant since fungus gnats love moisture so much.
Check the soil before you water your plant. The soil should be dry at least two inches deep before you even think of watering it.
Make sure your plant’s pot has drainage holes so extra water can escape instead of sitting in the potting soil.
How to Get Rid of Fungus Gnats
Detecting Fungus Gnats
Before you put your plant through a treatment, you need to know if what you’re dealing with are fungus gnats.
First, you need to look around your plant for the gnats. These insects aren’t hard to find.
But they’re hard to see so you’ll have to examine your plant closely.
Fungus gnats hang out on the top of the potting soil of a plant.
You’ll also notice the adults flying around the infested plant. But their wings aren’t made to fly for too long. They’re also slow fliers.
Adult fungus gnats tend to fly toward lights. When you have an infestation you’ll notice hovering around lights or windows in your home.
They won’t stray far from your indoor plants. The gnats don’t like to travel far from their homes because their wings are so weak.
If you still aren’t sure if you have fungus gnats, below are other signs to look for.
When a large number of larvae feast on your plant, leaves will turn a bright yellow. The leaves might even have brown or black spots. Then the leaves start to drop.
The growth of your plant will slow way down. The plant might even stop growing altogether.
The worse the roots, the worse the consequences. The plant will start to wilt. This will lead to your plant’s death.
One way to be sure you’re dealing with fungus gnats is to cut a raw potato in half. Place the halves the cut side down. You should place them on opposite sides at the base of your plant.
The fungus gnat larvae will crawl out of the soil to feed on the potato halves. The next day, turn the potatoes over.
You should see them crawling around. You might have to look close because the larvae are super small.
Small Fungus Gnat Infestations
You’re in luck if you catch a fungus gnat infestation before it doubles. There are a few great methods that will send those pests away for good.
For small infestations, you can use yellow sticky traps.
The only issue is this only rids your plant of adult fungus gnats. It doesn’t help you rid your plant of pupae or larvae.
You’re going to place the yellow sticky traps in a horizontal line on the surface of the soil.
The color yellow attracts fungus gnats. When they see the sticky traps, they’re going to head right for them.
Of course, the sticky surface traps these pests.
All you have to do is discard the yellow sticky traps. You’ll want to take the trash outside right away.
Try letting the potting soil dry down to two inches in depth. This takes all the moisture that the larvae love so much.
There are several benefits to this method.
First, the dry soil kills the bugs.
Second, it also stops fungus gnats from laying eggs and kills any eggs already under the soil’s surface.
You’ll have to find a way to treat your plant for the adult gnats.
To get rid of adult gnats, you can try hanging flypaper above your plant. But make sure you hang the flypaper high enough from your plant that it doesn’t get stuck to it.
At the same time, you don’t want the flypaper too high above the plant since fungus gnats are weak fliers.
Neem oil is perfect for small infestations of fungus gnats. It’s an all-natural pesticide that won’t hurt you or your plant.
Spray the neem oil on the top of the potting soil. Make sure you drench it. You should also spray anywhere you see the adult gnats flying.
When the larvae feed off soil that’s absorbed neem oil, there are strange effects. This includes the lack of wanting to eat or to mate. So, they die.
The oil will smother the adult gnats you spray. The oil is so thick it covers the gnat’s pores.
Neem oil also works as a great bug repellent.
Large Fungus Gnat Infestations
So, your fungus gnat infestation has grown large. It’s not uncommon for this to happen.
There a lot of cases when people don’t realize there’s a problem until their plant looks sick.
The problem with treating an infestation is that treatments only rid you of the adults or the larvae. Never both.
So, remember that you’ll have to do a combination of treatments to thoroughly treat your plant.
The first method to rid your plant of fungus gnats also works well for fleas. Gnats fly right into this concoction and fleas jump right in.
But it only works for adult fungus gnats.
- 1 cup of cider vinegar
- 1 teaspoon of mild liquid dish detergent
- 1 cup of water
- 1/4 inch deep shallow plastic container
In the shallow plastic container, mix the cider vinegar and water. Add the mild liquid dish detergent. You mix everything at this point.
Place the plastic container at the base of your plant, on the potting soil. Within the first day, you’ll see a few gnats stuck in the mixture.
You need to change out the container with new ingredients every three days at least.
Beneficial nematodes (also known as roundworm) are microscopic worm-like bugs. They’re perfect for fungus gnat control.
They’re easy to find. You can get nematodes online or even at some garden stores.
Don’t panic, they’re not the same roundworm that infests humans or pets.
These nematodes are natural enemies with fungus gnat larvae. You’ll be putting nature to work when you try this method out.
Nematodes can kill larvae in one of two ways.
The first way is by penetrating the larvae. The nematode enters the larvae through their mouths or pores. This alone can make the larvae sick.
The second way is by the nematodes releasing bacteria while inside of the larvae. These specific bacteria eat the larvae from the inside out.
Once this happens, the larvae have three to five days to live.
Nematodes work best between 60F to 90F.
Insecticidal soap is another great way to rid your plant of large infestations.
The soap is made from fatty acids. The fatty acids can cut through the gnat’s exoskeleton.
Once it’s through the exoskeleton the acids dehydrate the gnat, as the gnat’s cells collapse.
We have a soap recipe that will get those fungus gnats out of your plant’s potting soil.
- 1 tablespoon of pure liquid soap (you can substitute with mild dish detergent)
- 1 quart of water
- Spray bottle
Making the soap is simple and it saves you from buying an expensive version of the same thing.
Start by adding the water and pure liquid soap to the spray bottle. Shake it all together. If the pure soap is too thick, you’ll need to use a utensil to mix it.
Drench the potting soil of your plant with insecticidal soap. The soap will do the rest by seeping into the soil where the larvae lay.
You need to repeat this process every other day for about three weeks. This ensures that you get all the larvae that you didn’t get the first round.
You don’t want the females to lay more eggs in the soil you’ve already treated.
Now, this is only going to kill the fungus gnat larvae. You still need to take care of the adult gnats.
You’ll need a spray bottle for this next treatment too. You fill the spray bottle with only 3% hydrogen peroxide.
Only use 3% hydrogen peroxide. A stronger version can burn your plant since it’s a bleaching agent.
You can mix 3% hydrogen peroxide and water in equal parts to dilute it.
The first thing you need to do before applying hydrogen peroxide is to let the soil dry out for a few days.
Then all you have to do is spray and drench the potting soil with the hydrogen peroxide.
It won’t take long before you see the soil foam. This is how you know it’s working and killing the larvae on contact.
You’ll need to repeat this process once a week for three weeks or longer.
When all else fails, you might have to turn to chemical pest killers. Before you use these chemicals, test a small area to make sure there are no adverse effects.
Fungus Gnats FAQ
Why are they named “fungus gnats”?
They’re named fungus gnats because these bugs are carriers of mushroom spores. They come in contact with these spores because they’re attracted to fungi. When they land, their feet can (not always) spread the spores to your plant.
Why do the fungus gnats from my plant keep flying at me?
Fungus gnats are a nuisance when it comes to flying at humans. There’s something about us they like. If you wear perfume or cologne, they love you.
Do fungus gnats bite?
No, fungus gnats don’t bite. They’re harmless to humans and pets.
Fungus gnats are a nuisance and the larvae can be deadly. And the longer you let them go, the more they’ll multiple.
Once the infestation has grown, you’re going to have to work harder to get rid of these pests. The consequences could be dire for your plant.