Their life cycle consists of 4 distinct stages: egg, larva, pupa, and adult. In general, these gnats produce and develop faster with increasing ambient temperatures, but they can occur during any time of year in moist regions and indoors.

Female gnats lay eggs in moist organic debris or potting soil, commonly infesting any containers that are sources of organic decomposition. The larvae then feed on fungi and other matter in the soil. In some cases, they’re also known to chew on roots and leaves.

Since most of a fungus gnat’s life is spent as a larva and pupa, the most effective management approaches will focus on these early stages of life—as opposed to the short-lived, relatively harmless (but still irritating) adults.

Insecticides are an option to control these pests in a commercial setting, but this is usually excessive in a home setting.

Laying a layer of sand on the surface of the soil will help prevent the larvae from reaching the soil and feeding on decomposing materials.

Reducing excess soil moisture and organic debris is often the most effective treatment. Ensure your plants have good drainage, avoid overwatering, and do not allow water to remain stagnant.

Biological control agents, such as Steinernema feltiae nematodes or Hypoaspis predatory mites, can be purchased and applied to fight gnats.

You can also try to bait the female gnats with a good breeding ground, such as a pot of wheat and soil. The goal is to allow the females to lay their eggs in the lure, and then dispose of them before they hatch. Close monitoring should be exercised when trying this method.

Sticky traps are effective for trapping the adult gnats.

For potted plantings, allowing the surface of the soil to dry in between watering is important. Cleaning the area around your plant is also good practice. Picking out rotting leaves, which larvae will feed upon and nest within, is also recommended. Avoid using incompletely composted organic matter and excessive manure.

Using pasteurized container and potting mixes is recommended. Growers will often treat potting soil with heat or steam in order to kill flies and other microorganisms they feed on. At home, you can solarize your soil on a small scale in order to control soil borne pests with a non-chemical method.

To solarize your soil, you’ll first need to moisten it before placing it in a transparent or black plastic bag. Ensure the pile of soil is no deeper than 8 inches, then place the bag in a slightly elevated, sunny, hot location for 4 to 6 weeks. The effectiveness of this preventative method depends on the intensity, depth, and duration of the elevated soil temps it causes. In western Oregon, this is generally only possible during summer.