I feel your pain.... really I do. Fungus gnats are a blight, no doubt about it. I have tried many things, some worked some didn't. The best thing you can do for a bad infestation is get rid of the soil. (centipedes are pretty nasty, scary to me too!!!!)

I would ditch the infested soil altogether! there may be a way that is less traumatic to the plants, but I have found getting rid of the infested soil is the best remedy, especially when other plants are at risk.

Start with clean sterilized soil and fresh pots, dip all of the infested plants in mild soapy water top to bottom too. and repot into clean soil and pots. Good luck to you.

My rose cuttings are outdoors and doing fine, but the houseplants do get both centipedes and fungus gnats from time to time and I have found this to be the only really effective treatment for bad infestation.

Frances

Frances, thank you for answering! How in the world could I replace the soil? I have tens of pots everywhere in the house, from saved geraniums to a huge tropical tree to rose cuttings, african violets, you name it.... the only ones that don't seem to swarm with the buggers are the geraniums, everything else including the tropicals with their special soil is infested. My husband hates all my plants, but the truth is the little flies are falling in my coffee or in the soup they are everywhere, and at times it seems to be less and then they come back in bigger numbers. Is there any poison dedicated to them, that I could order from US? what we have in Canada nothing works....

BTW, I have several bags of soil in the basement, all started, and I have "some " flies in the basement too, even if I have no plants there...

Do a search for "fungus gnats" on line and you'll get a lot of information. Basically, you need to cut back on the watering and clean up any dead foliage - never let it lie on top of the soil in the pot.
Most sites recommend using yellow sticky cards to trap the adults that are flying about, and cut potato chunks laid on the soil surface will attract the larva. (Pick up the potato after a day or two and dispose of it along with the larva.) One site suggested that BT (Bacillus Thuringiensis, the same as you would use on caterpillars) will kill off the larva...but I only found that recommendation on the one site. Good luck. I know how upsetting these little pests can be. I had my best luck controlling them by letting soil completely dry out; rose cuttings probably won't take too kindly to this unfortunately.

Thank you, Anne , I know, I thought maybe someone had come up with an idea I haven't tried yet, worth asking. I did do the research and I applied all that was already said, including the sticky, it catches some but many still flying, they keep coming up. I also used BT, it smells bad and it's not working. Also tried the potato slices, stuck in the ground halfway, they turned black without catching anything. I keep the dirt so dry, it shrinks and peels off the walls of the pots, then I wet the cuttings sparingly from the bottom ( deep in a plastic tub) Nothing works. Tried diatomaceous earth too. God, I tried everything. Short of throwing everything out in the minus 20C, and killing them all i don't know what to do.
But thank you anyway, I'm still looking for a solution.
The idea to clean up whatever little leaf is falling is good, but I don't have much dead foliage....
thank you!

Log into Far North Gardening. There's a thread on about fungus gnats. Check it out.

Sengyan