How can I prevent drain flies from infesting my deck and yard?

Neil Young
by Neil Young

We have had an infestation of drain flies the past two years, but only when it’s warm (IL). I’ve been fighting them inside and searching for a source. Today I found a bunch outside under a low (3ft clearance) deck. It’s always moist under there as it gets no sun. Any tips on keeping it dry or at least discouraging the bugs? I had some river rock, but the sloped earth makes them slide out away from the house.Thanks!Neil

  4 answers
  • Lynn Sorrell Lynn Sorrell on Sep 02, 2019

    Inside your house around kitchen area? or inside around house plants? outside in yard/garden? Are they gnats or fruit flies?--- Fungus gnats are dark gray or black. ... On the other hand,fungus gnats feature dangling legs and long bodies that make them appear similar to a small mosquito. Eyes: Fruit flies are easy to recognize by their big, red eyes, butfungus gnat eyes are so small they are hard to see. Ones in kitchen are fruit flies Fruit flies lay their eggs near the surface of fermenting foods,drawn to sugery stuff or other moist, organic materials. ... Fruit flies are especially attracted to ripened fruits and vegetables in thekitchen. Wash produce as soon as you get home to remove any potential eggs or larvae.

    But they also will breed in drains, garbage disposals, empty bottles and cans, trash containers, mops and cleaning rags.Make sure all this is not attracting them.Get rid of them Fungus gnats Gnats reproduce in decaying organic matter that is moist and shaded. The larvae feed on fungus growing in the soil and moist organic matter. The larvae will also feed on live plant tissue, especially in root hairs and small roots. Get rid of them Mosquito dunks or bits in around house plants,gravel,lawns any where moisture issues are problem or buy Beneficial Nematodes add them to soil & sticky traps for flying ones here good site for all stuff needed

  • Neil Young Neil Young on Sep 02, 2019

    They are definitely drain flies, they end up around sinks and occasionally we’ll see larvae near drains. I have an idea how to contain them inside with drain enzymatic cleaner, but can’t get rid of them. I’m thinking this moist area under my deck might be the main source that I have not tackled.

    This is what the flies look exactly like:

  • Jan Clark Jan Clark on Sep 03, 2019

    Try covering the slope under the deck with a waterproof tarp. It will keep the area dry AND covered. Make sure you tack the edges with garden staples or something else to keep it from shifting and sliding away from the house. If you have power available, a box fan can also help dry it out after it rains. Hope that helps.

  • Sharon Sharon on Sep 05, 2019

    I would dry out the area under the deck, then use Rustoleum's Never Wet 2-part treatment . That should help the water bead and evaporate quicker. Then address the drain by using some borax pour down the drain.