What To Do If You Have Fungus Gnats in Your Soil
Most importantly, don’t overwater your plants! Never water cannabis plants grown in soil until the top inch of soil feels dry (up to your first knuckle). Fungus gnats need wet topsoil conditions to grow and thrive. The most common reason growers get fungus gnats is overwatering their plants.
Without Wet Topsoil, Fungus Gnats Naturally Disappear!
While the steps below will help you get rid of your fungus gnats quickly and effectively, the gnats will almost always go away on their own if you simply stop overwatering your cannabis plants. When there’s no fungus, there’s no fungus gnats, and both need wet conditions to grow. But if you already have them, here’s hwo to kick them out of your grow area…
Get Rid Of Fungus Gnats Quickly: What You Need
Yellow Sticky Cards
A Fungus gnat-killing product – I recommend Neem oil when you follow the directions and use a pressure sprayer/mister so it gets distributed evenly
Diatomaceous earth (food grade) and a powder duster to apply it
A fan to blow air over the top of your soil
1.) Place yellow sticky cards in the grow area – fungus gnats love the color yellow and will fly towards it. These yellow sticky cards (found at most gardening stores) are covered with a glue that will trap adult fungus gnats, bringing down their numbers.
But the most important reason to use yellow sticky cards is to help you keep track of how bad the current fungus gnat infestation is. As the infestation is reduced, there will be less adults caught in the yellow sticky traps. That’s how you know that your approach is working.
Place yellow sticky traps in the cannabis grow room Look at how many fungus gnats were caught in this sticky trap
Get Yellow Sticky Cards on Amazon
2.) Get a fan blowing air over the top of the growing medium. This helps dry out the top layer of your soil, and also helps prevent the fungus gnats from being able to fly around and lay more eggs.
Blow fan over the top of your growing medium to help combat fungus gnats
Get a Tabletop Fan on Amazon
3.) Don’t water your plants for a few days. You want to begin drying out the soil to kill as many larvae as you can before you apply a treatment (which will involve watering). Fungus gnat larvae need a warm, wet environment near the surface of your soil to grow. Even after you’ve gone through all these steps and believe fungus gnats are gone, make sure to avoid overwatering plants, as this is the most common reason growers get fungus gnats in the first place. Don’t do the next step until the top few inches of soil has dried out
4.) Kill the Larvae in The Soil
Treat top layer of soil with Neem oil (follow the directions and use a pressure sprayer/mister so it gets distributed evenly). Neem oil is safe to use up until a few days before harvest, though you want to avoid getting it on buds as it has an odd smell that can linger for a few days. Spray Neem oil anywhere you see fungus gnats, it should kill them almost instantly.
Get Neem oil online to treat your fungus gnats! A One-Hand Pressure Sprayer is perfect for misting plants
Note: Neem oil is great to have around the cannabis garden because it kills tons of different types of bugs, including Aphids, Barnacles, Broad mites & Russet mites, Caterpillars, cabbage loopers & inchworms, Crickets, Fungus gnats, Fungus/Mold (White Powdery Mildew, Bud Rot, Leaf Septoria etc), Grasshoppers, Leafhoppers, Leaf Miners, Mealybugs, Scales, Spider mites, Thrips and Whiteflies!
Use a powder duster to spread food-grade diatomaceous earth overexposed parts of soil. This will help kill the fungus gnat larvae and will also help prevent infestations in the future. While not completely necessary, adding diatomaceous earth is a great step to take to help get rid of the fungus gnats and their larvae as fast as possibleDiatomaceous earth is an organic insect killer made of fossilized shells. It is sharp on the microscopic level and works by puncturing the exoskeleton of insects (draining them of their body fluids), but poses no harm to humans or pets and can even be eaten.
Use a Powder Duster for the evenest coverage!
Get a powder duster to fight fungus gnats on Amazon.com!
Get Food-Grade Diatomaceous Earth On Amazon
Sprinkle diatomaceous earth over the top of your growing medium to help control fungus gnats
If you still have fungus gnats after doing that for a few days, try to mix it up because they will start getting resistant to your chosen treatment. Try one of these alternative cures:
Essentria IC3 Insecticide is a mix of various horticultural oils that is organic and safe for humans. It is often marketed as a “bed bug killer” but is also very effective against fungus gnats when the plants are treated regularly. You want to apply this every other days or possibly combine with other options. You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray the soil evenly, and make sure to follow the directions! Like all the options, it’s safe to use until a few days before harvest.
Get Essentria IC3 insecticide on Amazon.com - this can be a tool in the fight against broad mites or A One-Hand Pressure Sprayer is perfect for misting plants
BT Bacteria – Another thing you can water your plants with is something that contains “BT” bacteria (specifically, Bacillus thuringiensis var israelensis – there is another type of BT that’s meant for caterpillars), for example Mosquito Bits. However, they need to be crushed up into a powder so it will mix in the water for the best results when watering your plants. Just like any other time, always pH your water right before giving it to your plants!
Moquito bits kill fungus gnat larvae
Hydrogen Peroxide (food grade if possible) – If you don’t have access to any of the products, you can start getting creative at home. Usually, these types of remedies aren’t as effective as the “real” stuff but they will definitely still kill a lot of bugs! Use 1 part hydrogen peroxide to 4 parts water (for 3% pure H2O2) – another type of brute force attack to kill larvae directly.
Learn about “good bugs” that kill Fungus Gnat larvae below
5.) Avoid overwatering your cannabis plants from now on. Never water your cannabis plants in soil until the top inch or two of soil has dried out. From now on, you don’t want to ever let the top part of soil stay wet to create a breeding ground for fungus and fungus gnats. How often do I water my cannabis plants? Until the fungus gnats are gone, let your plant dry out a lot more than normal between waterings, and then you can go back to a normal watering schedule.
6.) Keep your sticky yellow cards up until Fungus Gnats are completely gone. These yellow sticky cards will continue killing adult gnats. They’re also helpful because they will alert you to whether fungus gnat numbers are rising or falling. Even after killing all the larvae, it may take a few days to a few weeks before the adult fungus gnats are completely gone and you stop seeing new gnats caught on your sticky cards.