just spotted a damn gnat flying around...damnit. I have an insecticidal soap spray. I just tried it on a piece of a plant to see if it will harm it. next up. potato slices...
From what I read you put 1/4 inch slices on top of the soil and the gnats prefer to place the larvae in the potatoes instead of the soil. Then trash the slices every 1-3 days till the gnats are gone. I'm about to start this tactic as soon as I get to the market for some papas, I've noticed I have a gnat prob as well, so if anyone would care to add please advise.
I use gardensafe neem oil about $4.00 at wal-mart.just have to make sure you mist underside of the leaves, and the soil........hope this helps.........