Are you seeing small flying insects on the surface of your growing medium? You may have fungus gnats. They’re often considered a minor pest but can quickly become a bigger problem. Here’s how to identify, get rid of and prevent fungus gnats in your cannabis plants.
What are Fungus Gnats?
Fungus gnats are about the size of a fruit fly and typically effect indoor plants. They’re attracted to the moisture in the medium. Fungus gnats can lay up to 200 eggs into the top layer of soil or coco coir, which will hatch after about 3 days. The larvae then burrow into the medium further to feed on fungi and decaying plant material. After two weeks, the larvae will emerge from the medium as adult gnats, who will repeat the cycle. Adult fungus gnats love for about a week.
Fungus gnats are completely harmless to humans because they don’t bite or spread diseases. Although, they can spread a plant pathogen called Pythium, which causes “damping off” in seedlings.
How to identify Fungus Gnats
Size: They are very tiny, ranging from 1.5mm to 3.0mm. The larvae may be up to 1/8 inch in length.
Appearance: Fungus gnats are grayish-black. They have long legs and antennae that give them a mosquito like appearance, but much smaller. The larvae have a small black head and long white or see through body.
Activity: They will typically spend their time on the surface of the growing medium or on the rim or side of the pot. Fungus gnats are not strong fliers, so they will fly in short bursts of erratic flying. They also have a tendency to fly directly at your face.
How to get rid of Fungus Gnats
I use a multiple step approach to getting rid of these gnats. You need to catch adults, kill larvae and eggs and help prevent them from coming back. These are the methods I use.
Cinnamon: This is an all natural fungicide. Simply sprinkle a generous amount of cinnamon on top of your medium, being sure to avoid plants as much as possible. This will kill the fungi that the larvae need to survive. If some gets on them, simply spray them with plain water and gently wipe clean.
Sand: Simply add a top layer of sand, about a 1/2″ to 1″ thick to your plant. This will dry out much quicker than soil or coco coir when watering, making it an unsuitable place for them to lay their eggs. This will help to prevent future infestations.
Hydrogen peroxide: To use this method, you need to mix hydrogen peroxide with water. I add 1.5 cups of hydrogen peroxide and 3 cups of water into a bottle to water my effected plants. Watering with hydrogen peroxide will kill larvae on direct contact. You will notice the medium fizzing up, this is normal and will subside. After the fizzing is done, it just breaks down into water and oxygen molecules. Repeat this treatment once a day into you no longer see gnats or larvae. This treatment can be repeated for up to a week.
Sticky Fly Paper or Vinegar Trap: You can use either of these methods to catch adult gnats. You want to draw them away from your plants to prevent further infestation.
For the sticky paper: Simply lay it out in your tent or grow area near your pots.
For the vinegar trap: Use a small jar and fill it about half way with either apple cider vinegar or white vinegar. Then, add a little squirt of dish soap. Finally, carefully poke some holes in the lid for the fungus gnats to get in. Place this trap near your pots to catch the gnats.
How to Prevent Fungus Gnats
There are a few things you can do to prevent fungus gnat infestation. First, you want to make sure your pots have proper drainage. You can do this by adding perlite to your soil or coco coir. Also, make sure your pots have sufficient damage holes. You should let the medium dry out in between waterings. This will deter gnats from laying eggs in the growing medium. Also, make sure to remove any leaves or debris from the medium. This eliminates a food source for the larvae.
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