What did it finally was a combination of sand in the pots, the bare minimum of watering, glue traps everywhere and some Neem tree oil directly in the water/soil. Also, quarantining plants with a lot of flies.
Been dealing with them a lot this year. Thanks for the tips!
Main tip, have patience. It takes weeks to get rid of them. Maybe you need to sacrifice a plant. But it is doable.
Bacillus thuringiensis israelensis is a bacteria that’s really good at killing mosquito, fungus gnat, and black fly larvae. It’s harmless to everything else and it’s the active ingredient in “Mosquito Dunks”.
You can break up a mosquito dunk into crumbles and soak them in a pitcher of water overnight to inoculate it with BTI. Water your plants with it to inoculate the soil and it’ll kill off the larvae – I go a little further and sprinkle crumbles over the soil in my pots to keep them inoculated.
It’s my go-to for dealing with fungus gnats in plants and I’ve never had it fail.
I have to remember that. I tried some nematodes that were supposed to eat the larvae, but it did not seem to work, even after a few weeks. The neem oil was mostly just for (against) plant lice, which it turned out to be doing jack shit to. But hey, the flies are gone, and the lice were contained by getting rid of the one plant that had the lice.
I eventually got tired of seeing the fucking gnats so I got some of the mosquito bits and made the tea, and they were gone the same day. Just have to remember to do subsequent treatments for 3 weeks so you get each stage in the life cycle.
