If you have houseplants, you may have experienced a nuisance insect called the fungus gnat. This tiny true fly is an inhabitant of moist soil where it feeds on fungi and organic matter found in houseplant soil – especially overly moist soil. If that is all they did, that would be one thing, but then these fungus gnats fly around and annoy you. I have ingested my share of fungus gnat over the years that flew into my mouth by accident! Can these strictly indoor pests be shown the door, or are there ways to suppress them to a level we can live with? Read on and find out.
Fungus gnats – or more correctly dark-winged fungus gnats – are generally known under the genus Bradysia. These minute insects start life as an egg hatching into a quarter inch long white to transparent legless larvae with a black head that can be seen with the naked eye. These larvae feed on organic matter, rotting plant material, fungi, algae, and sometimes the plant roots of seedlings and cuttings. A typical life cycle from egg to larvae to pupa and then to adult fungus gnat can – under normal temperatures – take no more than one month.
The main solution to control these flies is to reduce the moisture issue to make the environment less conducive to their propagation. Be careful how much you water your houseplants – do not water so much that it begins to accumulate and sit stagnant. Also, fungus gnats came into the house somehow – check for openings and examine new houseplants that may already have fungus gnats on-board. Monitor and use the famous sticky yellow traps – which not only help to give you an idea of the population – but also capture and remove a good number of individuals.
Another good suggestion is the use of biological controls to control the larvae. One such biological insecticide is Bacillus thuringiensis subspecies israelensis or (Bti). This material was originally formulated to control mosquito larvae. It also controls other Diptera such as fungus gnats. This material only targets the larvae and is easy and safe to use as per label directions – always follow label directions as the label is the law. Other biological methods of control include the use of beneficial nematodes and predatory mites. These options are very perishable, so you must be prepared to use them carefully and with knowledge of what it takes to keep them in good condition to work.
While it is always a best management practice to take care of an infestation while it is small, sometimes it can get away from you. Often, a potted plant is so infested with fungus gnats that you simply need to take it out and dispose of it. Eradication is often impractical or impossible, but using the cultural and biological controls noted above, satisfactory suppression can be achieved with fungus gnats to a level that most people can live with. Make a plan to tackle the indoor Beelzebub – fungus gnats – today! For more information on all types of house pests and their common sense control, or to ask a question, please visit https://www.facebook.com/CharlotteCountyExtension. You can also call the Master Gardener Volunteer Helpdesk on Mondays, Wednesdays, and Fridays from 1 to 4 pm at 764-4340 for gardening help and insight into their role as an Extension volunteer. Ralph E. Mitchell is the Director/Horticulture Agent for UF/IFAS Extension Charlotte County. He can be reached at 941-764-4344 or ralph.mitchell@charlottecountyfl.gov. Connect with us on social media. Like us on Facebook @CharlotteCountyExtension and follow us on Instagram @ifascharco.
Resources:
Mead, F. W. & Fasulo, T. R. (2024) Dark-winged Fungus Gnats, Bradysia spp. (Insecta: Diptera: Sciaridae) . The University of Florida Extension Service, IFAS.
Osborne, L. & Popenoe, J. (2025) Fungus Gnats. Mid-Florida Research and Education Center – Insect and Related Pests of Foliage Plants. The University of Florida Extension Service, IFAS.
Bethke, J.A. & Dreistadt, S.H. (2013) Fungus Gnats. UC Statewide IPM Program – University of California Regents of the University of California.
Morgan, J. & Suiter, D. (2022) Fungus Gnats – A Tiny Nuisance of Houseplants. UGA Cooperative Extension.
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