What are Fungus Gnats and How to Get Rid of Them?

Created by
Added 12 April 2022

We all desire big, bushy buds from our cannabis plants, but some pests can ruin it all. One of those pests is fungus gnats, which can significantly damage your plant if they are not eradicated on time.

Fortunately, you can easily eliminate them from your cannabis plant with a few tricks, which we will show you in this article.

What are Fungus Gnats?

fungus gnats cannabis

Fungus gnats are tiny, dark insects that look like small flies or fruit flies. If your plant has a fungus gnat infestation, you will often see them hopping around on the soil. 

Fungus gnats are different from other pests — they don't care about the buds or leaves. Instead, they feed on the roots. And since roots are so crucial for the plant's health, a severe fungus gnat infestation can claw away at the roots within a few days and significantly affect your plant's health. 

Lifecycle of a Fungus Gnat

fungus gnat lifecycle

The life cycle of a fungus gnat continues for a month. First, the adult female fungus gnat lays up to 300 eggs on the top of the soil in her final week.

Larvae emerge once the eggs hatch and feast on the root hair and soft tissue. After two weeks, the larvae move to the soil surface to pupate for 3 to 7 days. Then, the adult fungus gnat emerges and lives for around a week.

The good thing about a fungus gnat infestation is that it is not the worst your plant can experience. A mature, healthy plant with a robust root system can easily withstand the infestation, but seedlings and young plants are at the most risk of damage. 

Why Do They Attack Cannabis Plants?

fungus gnat infestation

Fungus gnats don't really care whether you're growing cannabis or tomatoes in your grow room — they only care about the roots.

However, it's not that simple. You'll see fungus gnats due to two primary reasons in cannabis plants:

  1. The soil is saturated with water (overwatering).
  2. The grow room environment is too moist or humid.

These conditions give rise to fungus, which these pests love (as their name suggests). So, they start making their home in your soil. Once the soil is depleted of fungus or organic matter, they start attacking the root hair and soft tissues.

The root zone is the perfect environment for fungus to grow. So, your plant's medium is an ideal home for them to eat and live in.

How to Spot Fungus Gnats?

fungus gnats on yellow traps

Fungus gnats are tiny pests that like to live in the soil, and are barely visible to the naked eye. So, the easiest way to spot them is to look closely at the soil — you will see them hopping or flying around the soil.

Another sign of fungus gnats is the presence of white maggots in the soil. These maggots are fungus gnats in the larvae stage. 

However, fungus gnat infestation also leads to other health problems for the plant since these pests eat away the precious root tissues. Some of such side effects of fungus gnats include:

  • Leaves yellowing, wilting, drooping, or spotting.
  • Signs of nutrient deficiency like stunted growth or discoloration of the leaves, despite feeding the plant with correct pH-balanced nutrients.
  • Plant experiencing slow growth and lower yield.
  • The seedling may also weaken and die.

How to Deal with a Fungus Gnat Infestation?

yellow traps set on plants

The good news is that fungus gnats are easy to deal with. In addition, their presence indicates that you are making a mistake with your cultivation, giving you a chance to correct it. 

Stop Watering for a Few Days

The most common reason for a fungus gnat infestation is overwatering, so you can simply stop watering the plant for a few days. Doing so would allow the soil to dry out, fixing the problem of fungus gnats on its own. 

You should also rethink your watering frequency or amount. For example, water the plant only when the soil at the top is completely dry to improve the aeration and prevent fungus gnats and other problems.

You can use the finger test to determine whether the soil is dry or not. First, stick a finger in the soil. Then, if it's moist, wait for it to dry. 

Or, pick up the pot and check its weight. If it feels heavy, wait for a couple of days to water. If it feels light, you can water the plant. 

Electric Bug Zappers

You know those devices that kill bugs? Typically, they are used for mosquitoes, but they work for fungus gnats as well. Although they won't get rid of every gnat, they work well to reduce their population. 

Use Yellow Sticky Traps

Yellow sticky traps are specially designed for insects like fungus gnats. These little cards attract fungus gnats, and they get stuck to them. Once you catch enough of them, simply dispose of the trap.

You can find these traps for cheap at your nearest gardening supply store, but note that they may not completely eradicate their population. For that, you must try some other methods.

Use Organic Pesticides

An effective way to kill fungus gnats is using pesticides like neem oil. You can also use Essentria IC3, a mix of various horticultural oils that serves the same purpose. These pesticides are relatively safe for plants yet effective at killing fungus gnats on contact. 

You can purchase them at your nearest gardening supply store and use them by following the instructions on the packaging. 

However, avoid using these sprays during the light hours as it can burn the plant, and never spray them on the buds. They can compromise the buds' flavor and aroma.

Sprinkle Diatomaceous Earth

Diatomaceous earth is a white powder that is harmless to mammals, but they are extremely sharp and deadly for insects at a microscopic level. It punctures their shell when it comes in contact with fungus gnats, dehydrating them. 

Get yourself some diatomaceous earth and sprinkle it on the soil around the plant. Doing so would take care of the problem quickly.

Point a Small Fan Towards the Soil

Since fungus gnats are a sign of soil being too moist, you can use a small fan to reduce the humidity within the soil. Ensure the fan blows air at a gentle pace that is enough to reduce the moistness in the soil. 

Too much air can dehydrate the soil too quickly, and your plant may even experience windburn.

Get Help from Predatory Bugs

You can even use predatory bugs who would love to feast on fungus gnats all day long. Some of the best anti-fungus gnat bugs are:

  • Rove beetles
  • Nematodes
  • Hypoaspis miles
  • Hunter flies
  • Synacra paupera

These bugs go around the grow room, eating up all the fungus gnats (and other pests) they come across. In fact, rove beetles also go within the soil to look for fungus gnats. And they are completely safe for your cannabis plant.

Preventing Fungus Gnats

Fungus gnats are a nuisance, and once you eliminate them from your grow room, you need to ensure they don't come back. Follow these tips to prevent another fungus gnat infestation.

Water Less Frequently

You must rectify your watering routine to keep the soil dry and avoid fungus in the root zone. Essentially, water the plant only after the soil has dried out and ensure proper drainage of the runoff water.

While the watering routine varies for each strain, it is not hard to figure out how much water your plant needs. The plant shows signs of underwatering or overwatering — look out for them and fine-tune your routine.

Cover the Soil

Fungus gnats often make their way to the soil and start multiplying within days. To avoid that, you can simply cover the soil with gravel, sand, perlite, or cloth to keep them from reaching your soil. Don't worry, fungus gnats do not harm your buds or leaves. 

Keep the Grow Room Clean

Decaying organic matter is a terrific source of fungus spores, which can quickly multiply and invite fungus gnats to your soil. So, keep your soil clean to avoid these pests from attacking it.

Sterilize Your Soil

Fungus gnats may even be present in the soil when you buy it, especially if you bought it from a local vendor. So, you must sterilize your soil to kill off their eggs and larvae.

You can do so by placing some soil in an oven-safe container. Bake it for half an hour at 82°F to 92°F or 27°C to 33°C.

Use Yellow Sticky Traps

Lastly, you can use yellow sticky traps. These won't ward off fungus gnats, but they are a good indicator of a potential fungus gnat infestation.

If you notice any fungus gnat stuck on the trap, you can then check your plants to look for any signs of other gnats flying around.

Summary: What are Fungus Gnats and How to Get Rid of Them?

Nothing is worse than investing so much time, effort, and money into growing a cannabis plant and some pests ruining it. So, you must try to prevent fungus gnats from harming your plant at all costs.

But if they do manage to sneak their way into the soil, follow the tips mentioned above to get rid of them.

If you ignore their presence, they can significantly harm your plant and lower your eventual yield. Plus, they will grow in number, and you will start finding them everywhere in your house. 

Use the method that suits you best to fix them and ensure your plant's soil is dry and fungus-free. That's all it takes to keep fungus gnats at bay.



Sort by
Small corrections, I noticed. The start of the article states gnats eat roots and mid way it corrects its self and gives the real diet of gnats, decaying organic matter, fungus and then roots when nothing else is left. bit misleading Diatomaceous Earth is only effective when it is dry and does not do anything when wet. if your applying a "dusting" onto the soil and its wet, this will be rendered useless until it dries out again. It is also a respiratory irritant and should be used with caution. In a tent with fans seems like a bad option for indoors and outdoors its an indiscriminate killer. "Bugs" are insects with six legs that belong to the group Hemiptera, Mites with eight legs and Nematoads no legs are not predatory bugs. but more so living/alive IPM options. BTi or Bacillus Thuringiensis Israelensis is a great way to manage Gnats and widely used in "organic" cannabis cultivation. Weird why it was not mentioned as a in water treatment.
@@NobodysBuds, I'll definitely try it if I have a gnat problem next time!
@m0use, I'll add BTI henceforth. Thank you :)
@@NobodysBuds, Initially, I had a problem with fungus gnats and I tried diatomaceous earth and sticky traps as well. Ultimately, I corrected my feeding schedule and the problem was solved. I haven't tried mosquito dunks, though. Will do it next time if there's a problem. Thanks for all your suggestions :)
Load more (1)