Fungus Gnat Treatment

Fungus gnats can stunt or even kill your plants.

Fungus gnats are just about 1/8 or 1/10 inch long. They have thin legs and a pair of delicate wings. Despite their frail look, fungus gnats can be quite a nuisance. Not only are these insects difficult to get rid of, but they also cause serious damage to plants. The larvae destroy the roots, affecting a plant’s growth, ultimately killing it.

Bacteria

Bacillus thuringiensis israelensis is a type of bacteria that is available under the trade name of Gnatrol. It is used as a soil drench and is most effective against the young fungus gnat larvae. Once the larvae ingest these bacteria, the microbes destroy the midgut epithelium of their host. The larvae stop feeding immediately and are killed quickly and effectively. This biological insecticide is popularly used in greenhouses to treat fungus gnats.

Parasitic Nematodes

Certain parasitic nematodes have been found to provide a long-term solution for fungus gnat infestations. Steinernema feltiae is one of the most popular of the various species of nematodes commercially available for fungus gnat treatment. These nematodes enter the larvae through their exoskeleton. Once inside the host, they release toxins that kill the gnat larvae. These nematodes are added as a drench to the potting soil.

Predatory Mite

Hypoaspis miles is a predatory mite that attacks fungus gnat larvae. These mites are mixed with the potting media before the plant is put in it. The mites are a hardy species; they can starve for long periods and even if the plants are not infested by fungus gnats, these mites stay alive in the soil feeding off other organisms.

Chemical Insecticides

If fungus gnats cannot be treated by biological means, then some chemical insecticides can be used. Pyrethrins or pyrethroids are effective against adult gnats. Other chemical drenches popularly used are carbaryl, malathion and diazinon. Repeat the treatment every few days for two weeks to get rid of fungus gnat infestations. However, chemical insecticides provide only temporary relief from gnats as they kill the adults and not the larvae.

Prevention and Control

Inspect a plant for fungus gnat infestations before you buy it. Use a sterile potting soil before planting a new plant or replanting an old one. If you put any plant outdoors, make sure that the plant does not have fungus gnats on it before you bring it in. Never overwater your plants. Ensure that the soil is well drained. Always use a container that provides efficient drainage. Do not allow any dead leaves or plant parts to collect on the soil, be it an indoor or outdoor plant.

References

• Ohio State University: Factsheet
• South Dakota State University: Fungus Gnats
• University of California: Managing Pests

Resources

• Texas Agricultural Extension Service: Fungus Gnat Management