In another similar thread somebody (I think KKfromNJ), mentioned a very good way to eliminate FG. Use just 1 teaspoon/gallon of GA "Knock-Out-Gnats" EVERY time you water, specially from day-one to inoculate the soil with the BT (bacteria). The BT only kills FG larvae (not eggs or adults), has something to do that disrupts their digestive system. Adults can be killed using regular insecticides (including soap) or place some of those yellow sticky sheets - horizontal is better the vertical). The adults are harmless, but a pain. Remember some sneaking up to my bedroom, and one day, I inhaled one though my nose - sen lurking around -and suddenly I felt a big 'itch' in my nose - guess it was it's frantic to escape my nose filtering hair... The larvae, which feed on decaying matter and ROOTS, DO the damage. I think that I only managed to see them only once - ~1/4" long translucent with a dark line along the middle (guess their gut) worm/moggot like critters. Also, somebody else (forgot who), mentioned that they seem to like MG potting soil (which I also use); either it already comes infested with (maybe eggs) or there is something in it that they specially like.

My grandfather used to control gnats in the house in a similar fashion. Put a banana peel in your stainless sink and let the gnats gather there. Bring in a small propane torch and make a quick pass over the peels. You might be able to use a bananal peel to lure the gnats away from your plant before you hit them with the heat gun. Somehow, I'm in love with the heat gun trick. It just seems very manly!

I hope it's okay to resurrect an old thread, but I have a question re mesh screen and fruit flies ... From this page here, http://homeguides.sfgate.com/determine-mesh-size-window-screen-25184.html, we can calculate how tight a mesh screen is by cutting out a 1 square in piece of fiberglass or other mesh screen and counting how many holes there are in that square inch to figure out the "density" or frequency of the holes to determine the size. But what size will actually keep out fruit flies, anyone know? I don't actually know the size of mesh screen holes that will keep these pesky flies out. Does anyone? I've looked and looked on the net but haven't found a thing. I brought home a roll of figerglass mesh home from my local hardware store but took it back yesterday because it seemed the holes were big enough for the flies to get through. At any rate, didn't want to risk it so didn't open package as the mesh wasn't cheap. Before I go out and buy again, want to know best size to use. Thanks for any help re this! :D

Potting soil is too water retentive or you are watering too often. Fungus gnats favor peat based soils so you might want to consider revamping your soil mix. As to controlling an existing infestation, you can repot, layer sand on the top of the soil surface (deters egg laying by adults) or you can dose with a dilute solution of hydrogen peroxide. And if you search the archives of this forum you will find many. many posts addressing the same subject :-))