Sooner or later, people who have houseplants get acquainted with fungus gnats.
These annoying little insects like to fly around your face when you settle into a lounge chair with a book or sit down to dinner, particularly in winter.
While fungus gnats are bothersome but harmless to people, plants don’t fare as well. The fungus gnat larvae feed mostly on fungi and decaying organic matter in the soil, but they’re not above nibbling on roots. If numerous, fungus gnats can damage plants and sometimes even kill them.
These little pests may hitchhike into the house with any plant you bring in, whether from your patio or a nursery.
Fortunately, fungus gnats are fairly easy to get rid of without bringing out the big guns. I’ve used a number of different methods, all with success.
If you start early, before the population of gnats explodes, yellow sticky traps may prevent an infestation before it begins. Adult gnats are attracted to the yellow color and get stuck, before they have a chance to lay their eggs in damp potting soil.
You can buy ready-made sticky traps or make your own. For homemade traps, I start by cutting a bright-yellow plastic disposable salad-size plate in quarters. Using Tangle-Trap, a sticky substance that comes in a can with a brush attached inside the lid, I coat both sides of each plate segment. Plastic card holders saved from floral arrangements work perfectly for keeping each trap upright in a plant pot.
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Besides trapping, it also helps to dump any standing water in saucers and to water plants only when the top of the soil feels dry to the touch.
In recent years, sand has become the weapon of choice for combatting fungus gnats. Simple as it seems, a half-inch layer of sand on top of the potting soil in each pot can keep fungus gnats from breeding. It works because sand drains and dries quickly, denying the fungus gnats the moist soil they prefer.
I’ve also had good luck using insecticidal soap to control fungus gnats. I make a solution of 2 tablespoons of the soap in a quart of warm water and use it to saturate the soil of each plant. Three weekly applications will do the trick.
If you have a lot of indoor plants or an out-of-control gnat population, treat the soil with a product called Knock-Out Gnats. After you scatter the granules on the soil, the naturally-occurring bacteria will be dispersed when you water the plants. Gnat larvae will quickly stop feeding and soon die.
You can order Knock-Out Gnats from Gardens Alive! (513-354-1482, www.gardensalive.com).
Jan Riggenbach writes her syndicated gardening column from her home near Glenwood, Iowa. See www.midwest
gardening.com for more information.