Fungus Gnats On Marijuana Plants


With my soilless mix, I’m using the drip system. When I moved the marijuana plant the other day, I noticed hundreds of miniscule white bugs in the standing water at the pail’s bottom. They’re fast, jumpy, and tend to form little colonies. What am I looking at here? Should I eliminate them?

The little white, water bugs are actually immature fungus gnats. They are detrimental to the marijuana plant because they suck on the roots and carry diseases. As they mature, they continue to eat plant debris and spread pathogens. You need to get rid of them.

In general, fungus gnats are black and around 1/16-inch long with a similar appearance to fruit flies. They hang around the planting medium, are vectors for disease, and their pupae live in the medium and feed on decaying organic matter. It’s not uncommon for them to pull in pathogens from other infected marijuana plants and then transfer it to the next plant. They are also, for some reason, drawn to the color yellow. If you want to figure out if your garden is infested, just hang a yellow sticky card up above it. If pests stick to it, then your marijuana garden is infested.

There are a number of ways to get rid of them that are harmless to you and your warm-blooded pets. The following pest killers are all organic and are frequently used on food crops as well. You can find them in garden shops or online.

Beneficial nematodes are small, wormy creatures that consume soil insects and their larvae. They are particularly effective at removing gnat larvae. Nematodes come in the form of a dry powder that you add to water. You can reintroduce them to the medium about every 4 to 6 weeks. They can be found at a number of nurseries and indoor grow shops.

Botanigard works on grubs and caterpillars, but it’s also effective for gnats. There is a living fungus in the concoction and it infects and terminates soft-bodied insects. The only focus of the fungus is infecting soft-bodied insects. It’s a lot like athlete’s foot, but far worse for insects. It comes in liquid form and is then added to water.

Gnatrol’s main active ingredient is the bacterium known as bacillus thuringiensis israelensis, which produces a plague among gnats. It will not affect other creatures and comes in the form a liquid concentrate. It is highly effective, largely because it lasts for up to two weeks ensuring that any new larvae are plagued when they hatch.

Pyrethrum is a pesticide created from a flower similar to the chrysanthemum. It is also toxic to fish so you shouldn’t use it by any water sources (or any pet fish). It doesn’t remain active for that long but it will get rid of flying gnats. The spray can be used as a powder, a bomb, or a liquid concentrate. Leave the room for a couple hours if you use the bomb. The active ingredient isn’t harmful, but it’s almost never good to breathe propellant fumes. You can use the concentrate or powders in conjunction with water to kill the larvae.