Shown is a bug trap, complete with several dozen captured gnats. This trap uses light to draw the gnats to the trap, and captures them with sticky materials that are refillable and unique to the specific brand. Photo by Jeff Burbrink.

By Jeff Burbrink
Extension Educator Ag & Natural Resources, Purdue Extension LaGrange County

LAGRANGE — For the past few weeks, we have been fighting some little annoying gnats in our office and at home. And judging from the emails and conversations I have had recently, so have quite a few readers of this column.

Winter is a common time to get these complaints. The critters tend to buzz around your sinks, houseplants and sometime the garbage pail if there is moist food scraps in the trash. More annoying, they get in your face. Thank goodness they are not known to carry diseases, right?!

There are several species of fruit flies, midges and fungus gnats that have earned the title “Most Annoying Winter Insect.” They feed on overripe fruit, food scraps in your trashcan, molds and fungi that accumulate in house plant soils, and the goop that builds up on the pipes in your sink.

Getting the little rascals under control hinges on removing access to their food supply and breeding locations. That’s easy to say, but hard to do, especially if you have a lot of houseplants in your home.

Food scraps can be stored outdoors in cold areas like unheated garages and in containers that do not allow mice or raccoons to fill their bellies. Boiling hot water or drain cleaners can remove the gunk from sink pipes, but will most likely need to be repeated a few times to see a reduction in gnat numbers. But houseplants need to remain in warm environments, and can serve as little gnat hotels for a few generations during the winter.

Some people have asked about insecticides. There are a few pesticides labeled for indoor use with flying insects. Many of these products contain pyrethrin, which will knock the offender out of the air, but will not give you any long-lasting control. Look for products that are labeled for houseplants. Some of the synthetic pyrethroids, with chemical names typically ending with the letters “thrin”, do have some residual effect, and could be used on the pots and soil surfaces, and maybe the leaf surfaces if labeled for that purpose.

There are several non-pesticide options too. Some yellow sticky traps can be purchased at hardware stores and greenhouses. These work in a similar fashion to fly paper, and can be placed near the plants and sinks, and will capture offending gnats. There are also plug-in light traps, which use light and a sticky trap to lure in unsuspecting gnats as well.

Regardless of your approach, it will take several weeks of persistence to truly reduce gnat issues inside a house. The job will be much more effective if you start with removal or reduction of their food supply first, and then go after the remaining critters with traps and insecticides.