Yup, I hear that ALL THE TIME. I usually keep quiet, cuz I just don't believe it. Maybe if they've been sitting outside in the parking lot of Home Depot all summer. But I get mine factory direct and store them dry.
I use Sunshine #4 and Canna coco. Dozens of 3.4 cu/ft bales per year. There has not been a single gnat in my garden in over 5 years.
If you have a little outbreak,
- soil drench with BT, nematodes or SM 90, and cover the media surface with a cover or some DE for the Larvae
- use TONS of Yellow sticky traps for adults (they go right for them, in my experience)
-Spray insecticidal soap also, if you're not budding.
-Most importantly, DON'T OVERWATER. Let the soil dry out once in a while, they like it. Especially the surface where the gnat larva are.
Fungus gnats need food. Which is usually organic material added to soil, or rotting roots from over-watered plants.