Don't bother with anything but the nematodes. I spent thousands of dollars buying yellow sticky tape, fungus gnat soil, sprays, everything. I even went online and tried all the home remedies. You can kill a lot of the adults but unless you get rid of the larvae, you won't get rid of them. The adults breed as soon as they leave the soil and have usually bred before you see them or before they land on the yellow sticky tape. I was swapping the yellow sticky tape every 2 weeks (1 week per side before they were completely covered in gnats) and I had over 20 bits of the tape in the 1 bedroom unit.
The fungus gnats got so bad here, there were literally hundreds of pairs breeding on the ceiling every day. They were landing on me, flying into my eyes, up my nose, in my ears. They landed on food and things I was washing. I was on the phone to the suicide help line a lot because of them. After nearly 2 years fighting them I saw an episode of Gardening Australia and they had a section on fungus gnats. They mentioned everything I had tried except the nematodes. I looked online, found a place over east that sells them. Ordered some, which arrived a few days later. Used them and no more gnats. I see the odd one here and there and they are from new plants I bought, but the only way to break the lifecycle is to kill the larvae while they are in the soil and you need the nematodes for that.
This was 1 week for this plant and each plant had 1 yellow sticky tape and I had 20 more sticky tapes in the unit. There's a couple of blowflies on the tape but most of the black specks are fungus gnats.
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