Fungus Gnats

Fungus Gnats are small dark flies often found in indoor cannabis facilities. Adults don't feed on plants, however, the larval stage actively feeds on plant roots as well as fungi and decaying organic matter. Fungus Gnat larvae, when present in large numbers, can damage roots and stunt plant growth possibly leading to significant yield loss.

Fungus Gnats are possible vectors of several diseases. Larvae can transmit root diseases such as Pythium, Verticillium, and Fusarium. Adults can vector airborne diseases such as Botrytis.

Overwatering is often the main condition favoring the development of fungus gnat. Fungus gnats are hard to get rid of if there are open bodies of water or exposed drains. Dead leaves, buckets of water, food, open trash cans, overwatering, can all lead to higher fungus gnat pressures. 

Warmer temperatures increase the reproduction rate. A female can lay up to 200 eggs that hatch in 2-3 days. At 75ºF, it takes more or less 17 days for a generation of fungus gnats to be produced. 

Damage symptoms and monitoring

The easiest way to detect the presence of fungus gnat is to look for adults with a simple visual inspection of the plants, the soil and in the indoor facility, or using sticky card traps.

How to control Fungus Gnats?

The entomopathogenic nematode, Steinernema feltiae, is highly effective when applied in large numbers. Depending on the Fungus Gnats population size, large infestations may require weekly treatments. Small infestations, and preventative treatments, can be applied every 2-4 weeks.

The predatory mite, Stratiolaelaps scimitus, is a soil-dwelling predatory mite that feeds on fungus gnats larvae.

A highly effective control strategy for fungus gnats is releasing both the predatory mite and nematodes at the same time.

Both of these natural enemies also feed on thrips pupae.


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