Life Cycle & How They Damage Plants
Fungus gnats develop through complete metamorphosis in four stages over a period of approximately three weeks in warmer conditions and up to six weeks in cooler conditions:
The adult cycle, when the fungus gnats are flying , only lasts about a week. Its during this time that the female lays eggs in the soilsometimes well over a hundred eggs at a time.
After hatching, the larvae stage lasts about two weeks.
Overwatering plants and water-logged soil are two common conditions that nurture fungi and attract fungus gnats to potted plants.
To survive, the larvae must eat and that may include feeding off your plant roots and root hairs within the soil or the stems of seedlings.
If there is enough damage, you may notice your plant is wilting or dropping leaves despite proper care.
The other concern is that both the adults and larvae can also transmit diseases such as pythium which causes damping-off disease.
Repot As A Last Resort
If things don’t start to turn around after a few weeks Jason recommends repotting with a new batch of potting mix to help reduce the egg count in the soil. Think of this as a last resort because there’s no guarantee the new potting mix won’t have eggs or larvae in it too.
“Even after repotting keep up the neem treatment and sticky traps.”
Sound like a lot? Jason is reassuring.
“Gardening is about adapting and it does get easier,” he says.
“Once you learn how to deal with gnats you won’t make the same mistakes again.”
Chrissi Charles is a queer writer and plant scientist passionate about propagating plant literacy on Wurundjeri country.
Dont Overwater Your Plants
Fungus gnats prefer damp soil, so the best thing to do is avoid overwatering your plants. This step is particularly important during the winter months when plants use less water. You also want to make sure that you dont use potting soil that holds onto water. Peat moss is an example of a medium that might retain moisture and encourage egg-laying.
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How They Impact Your Plants:
For the most part, gnats dont really affect your plants and they wont cause damage or stress to your leafy friends. However, if you have a plant that is already battling a fungus or other spreadable disease, a subsequent fungus gnat infestation can mean that travelling gnats can inadvertently spread that disease to other plants.
Nip The Problem In The Bud
Fungus gnats breed quickly and quickly create a full-blown infestation if you dont tackle the problem right away. If you bring home an infested plant, dont wait for it to become an unsolvable problem. Even one fungus gnat means there could be hundreds of larvae within the plant soil, eating at plant roots and ready to distribute their eggs throughout the rest of your house. Act quick!
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How Can You Deal With Fungus Gnats
Sticky traps work best for catching the adults. Since one adult can lay up to 300 eggs, this helps to slow population growth. Simply place the traps in your affected plants to catch the adults as they buzz by. You can pick up sticky traps from any local garden store.
For the larvae its a little different. We recommend using what is commonly known as ‘The Potato Method’. Since potatoes are starchy roots, the larvae will find them just as delicious as they find your plants. Cut off a few small chunks of potato and bury them in the soil around the affected plants roots. The larvae will attach themselves to to the potato chunks. After four to eight hours simply dig them up, throw them away, and repeat until no larvae are left.
This is very effective if your gnat infestation is mid to low level. If you have a lot of gnats in your pod, you can also try working with hydrogen peroxide. Remove your pod from the base and leave it somewhere sunny until the top layer of coir is totally dry.
Mix 1 part 3% hydrogen peroxide with 4 parts water, then drench the dry coir with this solution. After fizzing for about 30 seconds, the solution will break down into hydrogen and water both of which are harmless to your plants. This will effectively kill off most, if not all larvae. Its a good idea to use the potato hack after this to catch any larvae that might be left over. For an alternative to hydrogen peroxide, this same method can be used with neem oil as a substitute.
Inspect Your Plants Thoroughly
Most of the time, fungus gnats were already on your plant when you brought it in. Someone rarely has an indoor garden and suddenly finds a fungus gnat infestation six or seven months after getting their last plant.
Thoroughly inspect plants before bringing them home. Even the highest-quality plant nursery in your area may have a fungus gnat or too lingering. Fungus gnats are especially prone to the plants you buy at grocery stores or department stores, where little attention may be paid to them.
Ive been guilty of seeing a discount plant on a rack and taking it home with me just to find a fungus gnat infestation. If a plant is on sale, there may be a reason! Make sure to check your plant thoroughly.
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How Do I Get Rid Of Fungus Gnats In My Kitchen
Sometimes fungus gnats like to hover around the kitchen or bathroom, even if you dont have any houseplants in there. If youve been scratching your head figuring out how to locate their hideaway, chances are theyve been hiding in the drain of your sink! Bacteria can get trapped in the nooks and crannies of our sink drains, and the resulting funk draws in fungus gnats like a magnet. Flushing your drain regularly with bleach or peroxide will help to kill this bacteria, keeping your drain clean and free of fungus gnats.
A pest problem doesnt have to be a death sentence for your plants, so dont give up on them the moment you spot a few creepy crawlies! For more help identifying and combating plant pests or diseases on your houseplants in Edmonton, feel free to contact our experts or visit us in store. Well be happy to walk you through all the necessary steps to keep your plants safe and healthy! If you missed our previous installments on indoor pest control, check out our blog archives to discover our insider tips for tackling houseplant pests like a pro.
Selecting The Right Control Method
When fungus gnats get into your home, they can be very annoying. But their ability to annoy you can be increased or decreased by how you respond to them. There is a common method for eliminating fruit flies that has little impact on fungus flies. It is called an apple cider vinegar trap. While fungus gnats are attracted to the smell of vinegar, they aren’t as likely to climb into a hole to get to that vinegar as a fruit fly is.
You can, however, eliminate some fungus gnats by putting out an open bowl of vinegar. Some internet how-to videos claim that this will help you get control of gnats. But what these online experts fail to realize is that you’re only killing a small number of gnats, while feeding the rest. This allows the gnats to reproduce like crazy. This is definitely not the way to deal with fungus gnats.
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Be Careful Of Overwatering
Fungus gnats are highly interested in moisture, so they may float on over to your garden if your plants are exceptionally moist or grow a little bit of fungus. If you dont have any fungus gnats inside your home, you dont have to worry about this issue . However, with outdoor gardens, excess moisture might attract these gnats.
The Damage They Cause
In most cases, especially indoors, fungus gnats are harmless. They’re extremely annoying but won’t harm you or your plants in normal numbers. If you allow them to thrive inside to grow a large enough colony to harm your plants, you’ve got bigger problems than gnats.
In extremely large numbers, the fungus gnat larvae can eat enough of the roots of your plants to cause significant stress and hurt their ability to thrive and grow. This is particularly important if you’re dealing with seedlings, cuttings, and young plants.
They also carry a pathogen caused by fungi that they like, such as Phtophtora and Pythium.
When spread to your plants, this causes a condition called “damping-off,” which causes a thinner, constricted stem that causes the plant to be too top-heavy. It will fall over eventually and die. Please note that damping-off can’t be cured, only prevented.
Compost and peat moss as a potting mix is particularly easy to be affected by the damping-off fungus, so consider moving to a perlite or vermiculite mix instead.
Plants that are more easily harmed by fungus gnats are spider plants, wandering jew, types of geraniums, african violets, and peace lilies, so take extra care if you’re growing these. You’ll know there’s a problem if you start seeing poor growth, yellowing, and sudden wilting.
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How Do Fungus Gnats Affect Cannabis Plants
Fungus gnats affect cannabis plants in three main ways:
Over time, a fungus gnat infestation may drastically affect the overall health of your plants. Besides spotting adult fungus gnats buzzing around your plants, other signs of a fungus gnat infestation may include:
- Sick leaves that are pale, yellow, or developing dark brown/black spots
- Stunted plant growth
- Poor bud development
- Weak seedlings that “damp off” and die
Figure Out How To Get Rid Of Fungus Gnats
Fungus gnats are harmless pests to humans, but they can destroy your plants in a heartbeat. You dont want them around your house, so thats why you need to figure out how to get rid of fungus gnats. Work on preventative measures for all of your houseplants. If you notice any sign of them, start working on getting rid of them and remember be consistent.
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Consider Creating A Soil Barrier
Some people have also had success with adding horticultural sand or small pebbles on top of their potting mix. This can prevent female fungus gnats from being able to lay eggs in the soil.
Jason says it’s not his preference because it can make it difficult to see what’s going on in the soil but each to their own!
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The Venus flytraps were simply not up to the task. At one point there was a fungus gnat corpse in every single one of their sticky little mouths. Theyre so overworked and exhausted that they cant even close their tiny teeth anymore. The dead bugs have to wait their turn to be consumed. At the height of the issue, I estimate that I would have needed a carnivorous plant on par with Audrey II from Little Shop of Horrors to adequately address this. I did get to watch the flytraps bloom, though.
Jones, the beekeeper, recommended I try cinnamon or cedar shavings on the soil. She said the gnats dont like those scents, so they act as a deterrent. It did not seem that many were deterred.
The Katchy is a device with a little light that attracts gnats and mosquitoes and a window vortex that sucks them down onto a big sticker. It has captured a satisfying number of victims but does not fully address the problem.
Mosquito bits are little pellets that contain a bacteria thats toxic to fungus gnat and mosquito larvae. You scatter them on top of your soil or let them sit in your full watering can for a few hours or overnight to marinate. I tried both with limited results.
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Getting Rid Of Fungus Gnats Is Easy
The hardest part about getting an infestation of fungus gnats is learning to deal with them. Getting rid of them and preventing them is pretty simple, so the whole thing becomes quite the relief.
You just have to go through the process, which is a piece of cake. And then you’ll have supplies on hand for next time.
Organic Fungus Gnat Control
Interestingly enough, a common household item is one of the top recommendations that I have for controlling these pests. Hydrogen peroxide can be used as a soil drench.
Mix one part peroxide with four parts water, and pour it through the soil at the root zone until it begins to come out of the base of the pot. The peroxide kills fungus gnat larvae on contact.
Neem oil is also an effective soil soak to combat fungus gnat larvae. Dilute the oil with water per the manufacturers directions and directly drench the soil at the roots of the plant. You can also spray the upper portion of the plant to keep adult gnats at bay.
Concentrated azadirachtin naturally occurs in neem oil. Its safe in hydroponic use as well as in greenhouses, gardens, and indoors. Use it per the manufacturers directions in the same way you would use neem oil.
Pyrethrin sprays are also effective against fungus gnats and their larvae. To use pyrethrins, lightly mist all plant surfaces and the top of the soil. You dont want the plants dripping wet, a thin mist will be enough. If there are fungus gnat larvae in the soil, spray the soil directly where adults typically rest to thoroughly moisten the top, then avoid overwatering. Let the soil dry to at least a 2 depth. Reapply these in three to four weeks until the problem has subsided and the insects are gone.
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Fungus Gnats As Disease Vectors
Yes, fungus gnats damage plants, but its important to kill fungus gnat larvae and adults because they can carry diseases. Those recovering from fungus gnat problems still face the risk of infections. Fungus gnat larvae can spread fungus spores that are dropped by adult gnats to your plants roots, possibly causing a number of common plant diseases. The most commonly transferred diseases include black root rot, Pythium blight, Verticillium wilt, Botrytis blight, and Fusarium wilt.
As a precaution, treat any affected plant and those in the area with a copper fungicide a day or two after pesticide application. This ensures that if your plant had contact with potentially dangerous disease fungi spores, they wont contract the disease. A root drench is more effective than spraying the plants foliage, as thats where damage would be done.
What Fungus Gnats Look Like
- Appearance: similar to mosquitoes but much smaller
- Adult size: average 3mm or 1/8-inch long
- Color: dark brown or grayish black
- Parts: Long legs long, segmented antennae translucent wings that fold together on their backs
- Behavior: weak fliers that cant travel farit looks more like hopping than flying
Fungus gnats look like little mosquitoes but unlike mosquitoes they do not bite people or animals.
While there are other flies that fit the fungus gnat description, a tell-tale sign is how the adults move, appearing to hop fairly short distances in a disorderly fashion, rather than flying more proficiently.
Fungus Gnat Larvae
Fungus gnat larvae have translucent bodies and shiny black heads. They measure about 1/4-inch long or twice the length of the adults.
The Potato Trick
If youre pretty sure you have fungus gnat larvae but cant find them by combing through your potting mix, you can try the potato trick to attract them.
Place a 1/4-inch slice of raw potato on the potting mix. Any nearby larvae should come dine on the underside of the potato slice within a few days.
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Dont Overwater Your Houseplants
Make sure you arent overwatering your plants. Moisture is a big plus for gnats, so to make their new environment inhospitable, you need to let the soil they live in dry out completely.
Neither adult gnats nor their larvae can survive in dry soil, so let your soil dry out completely between watering as often as possible. Heres an entire guide devoted to teaching how to water your houseplant properly.
Cultural Control Of Fungus Gnats
Do not overwater your growing media. Waterlogged growing medium in houseplants is a prime breeding ground for these insects. Dont allow standing water to remain in saucers below houseplants or near growing media for long. Repair any irrigation system leaks that crop up, and keep your growing medium away from your potted greenhouse dwellers. Pasteurize the compost in your growing medium to eliminate any larvae that may be feeding on the organic materials there. Use commercial growing medium blends that have been treated with heat if youre not into the idea of doing it yourself. Move any infected plant matter and growing medium away from others while you treat the problem.
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Fungus Gnat Lesson #: Harsh Treatment Options Areharsh
When I was first dealing with fungus gnats, I went directly to internet search engines to look for treatments. I found a ton of recommendations, but decided to try a hydrogen peroxide flush to remove the gnats and their eggs. In my experience, this harsh treatment did kill the gnatsbut unfortunately, it killed my plant, too. Theoretically, this treatment is ideal because it would kill the eggs, the larva and the mature fungus gnats. However, I found it really taxing on the plants I tried it with, and I lost a pothos in the process.
My tried and true treatment options include the following:
- Preventative neem oil treatment: I add a few drops to my watering can, and dilute it in a spray bottle to polish the leaves of my plants. Fungus gnats hate this stuff, so the idea is that the neem oil will make the environment inhospitable to the unwanted bugs.
- Sticky traps: these traps can be placed in your plant pot to catch mature gnats on their sticky glue.
- The apple cider vinegar trick: Occasionally, when gnats try to make an appearance in my home, I fill a small dish with apple cider vinegar and leave it out to trap the bugs. They love vinegar, and willingly fall into the bowl. Its an easy, cheap option to help keep their numbers down.
