I would really hold off on soil drenches of any sort until the seedling is into its veg stage and not so vulnerable to stressors.
Fungus gnats are luckily not one of the more damaging pests that you will find in your garden- an annoyance for sure, and a vector for disease, but not as damaging directly as mites or thrips.
They like it wet, and depend upon standing water or sodden soil (mud) to breed, so eliminating these from your grow area is the place to start treating them. This includes any trays underneath pots- lift and clean these regularly. Scrub them down with a stiff brush to get caked dirt off, and then spray with foaming bathroom cleanser, allow to sit ~15 minutes, and rinse before returning to the grow area.
Gnat infestation comes with poor attention to growroom cleanliness or leaks... no standing water! No mud! No buckets of used dirt in the corner just sitting there waiting for bugs! It's like a neon sign outside a cheap motel off the Strip that says 'hourly rates! king size beds!'
stinkyattic Reviewed by stinkyattic on . Fungus Gnats I have a fungus gnat infestation starting. I need to end it ASAP. I've searched for Bacillus Thuringiensis Var. Israelensis and products that contain it and haven't found much. Can anyone hook me up with some experience here? What product should I use and where can I get it? My hydro store is pretty small so I don't know if they would carry it or not. Also I am using a No Pest Strip currently. Rating: 5