Answer: Fungus gnats are pesky once they get established. They reproduce in the top layers of moist soil. I'm not aware of a chemical that works on them. Before completely repotting, try scraping off several inches of the top soil and letting the plants dry out for a bit. That will get rid of quite a few of them since they won't have moist soil. (Of course, you can't let them dry out too long or it's detrimental for the plants.) Then repot, and try putting some plastic wrap or other barrier over the soil. The good news is that fungus gnats don't live very long.
Q&A Library Searching Tips