comments:
If you still have an issue with fungus gnats after the nematode treatment, try mosquito bit tea. You just soak the bits in water and then use that water to water your plants. Put sticky traps in your pots to catch the adults and the tea will kill the larvae. There’s also drops like this one. I had a small gnat problem last year and someone on one of these subs mentioned this stuff. I grow ferns indoors who have to stay pretty damp all of the time. Now I just put a few drops of this in my watering can every time I water and my gnat problem is gone.
https://www.amazon.com/dp/B007UTE55A Grab a bottle of this. Put a couple of drops of the liquid into a gallon of water. Use that water and that water only to water your planted tank. 2 ounces of the stuff will last you ages. It's the same ingredient as in "mosquito dunks," which someone will be around to recommend shortly, but without the nasty smell and decaying corn from the dunks.
There could of been eggs in your new soil and now they’ve hatched. It happens. I wouldn’t worry about them harming your plant. It would take a crazy amount of the larvae in your soil to actually cause damage to your plant. But, it does need to be addressed. Sticky traps and mosquito dunks is a good way to go. I actually use this stuff, it’s just easier than making the tea, but it is more expensive. I just squirt some of this stuff into the water I use to water my plants. I use it every time, with or without gnats and it keeps my plants gnat free.
BTI concentrated drops and the yellow sticky sheets. Use more than a drop per gallon in every watering, even when the gnats are gone. It should take about 2-3 weeks or 3-4 waterings to really work. Sticky traps kill the adults, and the drops kill the larvae. Don't stop using it. Repotting with new dirt, bringing new plants in, will bring fungus gnats back. Good luck! https://a.co/d/09oS6azT
These drops with every watering will destroy them. Also put way more yellow sticky traps (like an absurd amount) on the top around the pot to maximize capturing the adults. The drops will poison the larvae in the soil with every watering. Do not water more than needed, dry out 80-90% before waterings. Make sure the plant is in a sunny spot to speed up water transfer. The cycle must be completely stopped from all stages of the fungus gnats growth cycle. You can google that to see the full cycle if you’re curious. Don’t waste your time with “natural” cures like neem or peppermint oil, they don’t work for severe infestations. The stones aren’t helping, gnats are tiny and the spaces between the stones might as be the Grand Canyon to them!