Fungus gnats are a persistent problem in marijuana gardens.
They’re tiny flying insects that can live in soil, inert material (such as coco coir and rockwool) and soilless mix.
Fungus gnats can’t take hold in pure hydroponics, such as deep water culture or aeroponics. They enter your marijuana grow room via contaminated root zone media, air, pets, windows, doors, attics, clones and people.
The juvenile (larval) fungus gnats live in the root zone. They eat marijuana roots, organic nutrients, debris and other organic materials.
When the larvae mature to become adult, they fly around seeking new places to lay eggs.
Fungus gnats are attracted to your cannabis grow room because they like moisture, food and light.
If you’re using most brands of organic nutrients, soil or soilless mix, and especially if you overwater, you’re providing an ideal environment for fungus gnats.
The main damage from fungus gnats come when their larvae eat the tender roots of seedlings, clones and plants younger than a month old.
Root damage leads to decreased intake of water, nutrients and oxygen, which in turn leads to slower growth and smaller yields.
It also creates the opportunity for root zone diseases to attack your roots.
Here are the ways you block and stop fungus gnats:
- Let the top 2–3 inches of your root zone dry out.
- Don’t overwater.
- Block all vector channels that bring fungus gnats into your grow room.
- Beware commercial soil, especially so-called organic soil.
- Put yellow sticky traps near your root zone.
- Use only quality organic nutrients such as Iguana Juice. Most organic nutrients create a dirty environment in your root zone. Iguana Juice doesn’t.
- Use this natural insecticide.
- Use sterilized soil or soilless mix.
- Avoid using regular organic nutrients. Try Iguana Juice Organic instead.
- Feed beneficial microbes to your root zone: Voodoo Juice, Piranha, Tarantula.
- Use Sensizym, which breaks down organic materials in the root zone.
- Fungus gnat larvae live in the top 1–2 inches of a marijuana root zone. If you remove the infected root zone’s top layer and replace with fresh, sterile material such as rockwool or perlite, you remove most if not all of the fungus gnat larvae.
- Use beneficial predators (hypoaspis predatory mites) or a biological insecticide containing bacillus thuringiensis that attack fungus gnats.
- If you have persistent fungus gnat issues, the most likely causes are inferior organic fertilizer and overwatering.
- DO NOT put diatomaceous earth at the top of your root zone, as some people mistakenly recommend.
Fungus gnats aren’t the worst pest you’ll have in your marijuana grow op, but you’ll do well to stop them from being there.