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Get Rid of Fungus Gnats

You don't have to cohabitate with these tiny pests

Don't fret: You can banish these annoying pests in not time. Click to enlarge image Don't fret: You can banish these annoying pests in not time. Photo/Illustration: Steven Cominsky
Gnats are annoying: They quietly fly around, often just a few inches from your face, daring you to catch them. As a plant lover, however, the fungus gnat may be the most irritating pest of all. Though harmless to humans, fungus gnats can multiply rapidly in indoor plants, laying their larvae in the top layer of potting mix.
These pesky gnats can be brought indoors from outside plants during overwintering. More often than not, however, they are transported into your home by infected plants picked up at the nursery or garden center. They love to hide in overly moist soil full of decay­ing plant matter. Once they are introduced into one plant, they easily make their home in other nearby plants, their larvae happily awaiting birth in the first inch or so of soil. Larvae primarily survive off fungi found in the soil but may also feed on root hairs. As the adults lay their eggs and multiply, the infes­tation continues to grow.
Rest assured, however, that you can get rid of fungus gnats without having to trash all of your plants. If the infestation is new, let the soil of infected plants dry out completely, which kills the larvae. If the infestation is beginning to grow, however, you’ll need to take more serious action. You could catch the adult fungus gnats using sticky paper, but that will not eliminate the larvae waiting to hatch. I’ve found a common, safe two-step home remedy (sidebar, right) that cures the entire problem. You’ll need sand; several small saucers; and a nice, fruity drink—for the bugs, not you.

2 Steps to gnat-free

Click to enlarge image Photo/Illustration: Steven Cominsky

Step 1:Make the sand trap Collect all infected houseplants, and remove the top 2 inches of potting mix to dispose of the larvae already laid. Discard the soil immediately, and replace this top layer with sand, which is free of organic matter and dries out quickly—an unappealing medium for fungus-gnat eggs. Let the soil below dry out completely before the next watering. This should eliminate all fungus-gnat larvae present and prevent new eggs from being laid.

Step 2: Set up the open bar Adult fungus gnats are easy to lure and drown  using any sweet liquid that smells of decay. A nice $2 bottle of alcohol-free wine from Trader Joe’s is one of the best and cheapest fungus-gnat baits I’ve found. Pour the liquid into a small saucer, and place it near a previously infected plant (or by all infected plants if the infestation is already rampant). If you let it sit overnight, then you should awake to a disturbingly satisfying collection of dead fungus gnats floating in the liquid. Discard and refill the saucers until the adult gnats no longer appear.

From Fine Gardening 131 , pp. 70