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Fungus Gnats Are Common Where There Are Potted Plants

By Chris Williams on May 26, 2016.

When we get a customer complaint about annoying little gnats flying about the house, we can usually narrow it down to four possible flies: fruit flies, drain flies, phorid flies, or fungus gnats (see Tracking Down Indoor Gnats). All of these are “wet gunk” gnats; they are associated with some type of organic “goo” and moisture. They’re all small and dark and can be hard to tell apart without magnification.

If the homeowner mentions houseplants in the same breath with gnats, we zero in on fungus gnats. These flies are only 1/16-inch long and look a little like miniature mosquitoes with their pointed abdomen, long legs and long antennae. The female fly lays her eggs in wet potting soil where the long, wormlike larvae develop. When the adult gnats emerge from the pots, they stay near their breeding site and may be seen hovering around potted plants or running on surfaces in a jerky manner. They are attracted to lights and windows and are apt to hover in front of the television.

Although overwatered house plants are the main source of fungus gnats, they can also be associated with water leaks where excess moisture has allowed fungus to grow, or with wet, decaying vegetation, even wet feces in bird cages (see Finding Fungus Gnat Breeding Sites). Fungus gnats can also be major pests in greenhouses or in commercial mushroom growing operations.

Fungus Gnat Control? – You Can Do It Yourself

Fungus gnat larvae living in potting soil are generally not noticed. They are mostly nuisance pests but can damage plant roots if they are present in large numbers. If you know the source of fungus gnats, getting rid of them is easy and doesn’t require the use of pesticides. Simply dry out the site. Allow potting soil to dry out completely between waterings. Fungus gnat larvae require damp soil and can’t survive if the soil dries out. Repotting the plants in new soil is never a bad idea either.

This simple solution can be difficult for those who are used to watering houseplants on schedule every couple of days and can’t stand the idea of dry soil. In my home, the potted plants thrive on neglect so fungus gnats are rarely a problem. For more on control measures, see Fungus Gnats? – Lose the Watering Can.

Photo Credit : “Female black fungus gnat” by EBKauai | CC BY 2.0

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