Posted on by Alex Thornton

Pests - Fungus Gnats

Fungus gnats are small flies very similar to fruit flies that are part of the Mycetophilidae and Sciaridae families. They feed on decaying organic matter, fungi and plant roots (especially damaged roots making plant much more prone to diseases).

Fungus gnats are particularly dangerous to plants as they can also carry diseases such as Pythium on the feet and transfer it from plant to plant.

Their life span consists of about 3-4 weeks depending on the conditions of the environment. Fungus gnats love damp moist (overwatered) mediums, as they breed extremely fast in these conditions (up to 300 eggs in an adult’s life) and benefit from high humidity.

These gnats have 4 stages of life: egg, larvae, pupae and adult.

The eggs will hatch after about 3-6 days, hatching little larvae.

The larvae feed on the fine root hairs of the plant and will do significant damage if feeding on a seedling/cutting or an unestablished plant, but if you have a large healthy established plant the larvae will barely effect it.

Fungus gnats are pretty easy to control if the infestation isn’t too bad, but if infestation is bad, your fruits/flowers will act as sticky traps.

Gnatnix - Fungus Gnats - A-Grade Hydroponics

We always aim to terminate the adults to prevent further eggs being laid, we can do this with a natural pyrethrum spray. Just spray on top of the medium, tap the pot a couple of times and you should notice more adults fly out which you can then spray, aim for the larvae, as they are the easiest to kill. A 3% Hydrogen Peroxide (H2O2) flush through your medium should instantly killing all larvae as well. Keep this method up for about 3 days and that should kill and completely destroy their life cycle, preventing a further cycle from occurring.

A great prevention for fungus gnats is to lay a small layer of sand about 1mm then another mulch above the sand of Gnat nix about 2-5mm, this will prevent any fungus gnat growth. Make sure you also line the bottom of your pots with gnat nix to prevent them from breeding through your drainage holes.