For years I have fought these almost gnat-sized black flies that,I believe, come indoors in the plants I've set out during the summer. Then they drive us insane by buzzing around our faces. Guests think we're nuts, or seeing things as we wave our hands in the air. And the little buggers won't leave you alone. They seem to live in the soil and do cause damage to the plant. Also, they tend to infest other potted plants that have stayed in the year-round. I've tried everything from comercial pesticides (all types) to homemade concoctions. Nothing works. Please help me to identify and KILL these little pests!!!

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RE: Teeny -Tiny Black Flies Brought to you by
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Posted by botanybob Northern Idaho (My Page) on Thu, Oct 4, 07 at 18:21

You have fungus gnats. These tiny flies lay eggs in moist potting soil. The larvae live in the soil and feed on fungi, algae, and roots. Most plants can tolerate their presence without sustaining any damage.
First it is helpful to watch your watering and only water plants after the surface of the soil has dried. Keeping the surface constantly moist will encourage the flies to lay eggs. You can add a layer of coarse sand on top of the potting soil to provide the same effect.

You can treat the soil with BTi, sold as Gnatrol, which you will probably have to order online or through a catalog. You can make your own concoction from Mosquito Dunks, which have the same ingredient. These are more common in stores. I've not done this myself, so hopefully some other gardenwebber can supply details.

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Posted by morz8 Z8 Wa coast (My Page) on Thu, Oct 4, 07 at 21:30

Hoya, BotanyBob is completely right - they are fungus gnats.
The BTi is a very effective, safe non-chemical way to rid your pots of the gnat larvae and stop the breeding cycle. (you are going to continue to notice the adults for several days, but they don't cause the damage and the larvae are your target pest)
Gnatrol and KnockOutGnats are both available as a liquid condensed version of BTi. If you can't find those (or any other BTi (Bacillus thurengienesis subspecies israelensis)liquid product, you can make your own by floating a mosquito dunk in a container of water overnight. Save the dunk for future use, intermittent wetting and drying doesn't alter it's effectiveness. Use the treated water just as you would use the Gnatrol or KnockOutGnats - water your containers with it three consecutive times on your own normal watering schedule.

I'm noticing the gnats around some seedlings pots right now myself - the pots aren't coming in for winter but I don't want the larvae feeding on fine roots during our wet mild Fall so I'll start treating this week here :)

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Posted by kimmsr 4a/5b-MI (My Page) on Fri, Oct 5, 07 at 7:40

While the BTI is a good control the single best way to keep these Fungus Gnats in control is to watch the watering of your plants. Check the soil to a depth of 2 inches, roughly the first knuckle of your index finger, and only water if the soil in the pot is dry to that depth.
You could also repot your plants with a fresh soilless mix when you bring those plants in.

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Posted by hoya-honey (My Page) on Sat, Oct 6, 07 at 14:25

Thank All Of You SOOOOO Much!!! This is the first I've ever heard of these pests. It really pays to ask the professionals. Will let you all know how it goes. Thanks again.

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Posted by betula_pondula (My Page) on Mon, Nov 3, 08 at 13:03

Hey everyone i just wanted to re-open this thread because im having a bit of a problem right now. These dumb little flies are living in my Black Oak's soil now and I dont know how to get em out. I know there is those products but I am wondering if there is any natural remedys. I will buy the product if nesicary but i just want these flies gone I read something about onions and spraying water on the soil to ward them off. anything that you think would help.
thanks