Ahhhh the elusive Fungus gnat.... I will leave that to the experts here.
You WILL get a great answer here.

The vinegar works for fruit flies, not fungus gnats. They are a problem. I'd lift the plants and thoroughly wash off all soil, then dip the roots in a mixture of a 2 cups water with a tablespoon of Simple Green and a tablespoon of isopropol alcohol. Let the roots sit in the liquid for a couple minutes. Repot in a sterile potting mix and either use new pots or wash and soak the old ones in diluted bleach. This is something new I'm trying and it seems to be working. Make sure once they are repotted that the soil isn't kept wet and always water from the bottom. You can spread a layer of fine sand on the soil surface to discourage the gnats from returning but if you had any other plants nearby they might be infested too. A mature plant isn't usually affected by fungus gnats. It's seedlings and newly rooted cuttings that are damaged. The gnat larva feed on the roots. I also water my seed trays with water that contains Bt. I just take a mosquito dunk and let it sit in a gallon of water and use that on the plants. You can keep using the same mosquito dunk for quite some time.

Thanks so much for answering to quickly, I'm about to walk out the door and will get all that I need. Geeze, what a PITB!
but I will do all to save my babies!
Thanks again Karyn.

I was just waiting for this topic to show up this year! That is the one thing I hate about having plants indoors during winter. I still have my brug cuttings wrapped in sphagnum moss and don't want to plant them because I hate dealing with those nasty gnats!

Karyn have you had success with completely uprooting the plants? I'd be afraid of them shocking and dying with all that root disturbance. Or maybe I'm just not gentle enough. Anyway, I've had great success with fungus gnats by using the soil drench "Knockout Gnats" available on Gardens Alive. If the infestation isn't so bad, you can always scoop out the top 1 or 1 1/2" soil where the eggs are laid and replace it, then cut back on the watering too. Then there's always a systemic insecticide which I'm a big fan of during winter, too. Keeps all the nasties at bay while the plants are inside.
Diane

Knockout Gnats is Bt, just in another form and more expensive. lol I've had good luck with completely uprooting the plants. They do shock a bit but if left alone with the fungus gnats they'll die so it's not much of a choice. I've used Bt for years and it never seems to completely eradicate an established gnat infestation but it does work as a prophylactic measure. I don't use any systemic insecticides or insecticides in general except for Forbid and Floramite.

Hello all: I have also had a problem with fungas gnats but my control method is low tech and also probably not as effective as the chemical controls Karyn and others deal with...but certainly does the trick temporarily. I use the rodent glue boards and hang them around my lights in the plant room amongst the plants. If I put them up at night, by morning I will have trapped dozens. Just a suggestion but not a cure.Vaseline spread thinly on a piece of white cardboard also is effective in case you can;t find the glueboards. Ross.

Ross I also use the sticky boards but the ones made for gnats & flies, not rodents. The rodent traps sound like they'd be equally effective and less expensive. I'd never thought of using them. Thanks. The problem with sticky traps is they'll only trap adult gnats but it takes a long time until all the larva emerge and they are the ones that cause damage. I tried making the boards with yellow cardstock and vaseline. What a mess! lol I ended up with half of it in my hair. Note to all with long hair. Tie it back first!!!

If you use Bt, then you don't need to do any digging at all. I use just 3 drops of a mosquito control liquid made for ponds in a standard quart mister, it does over a hundred plants for me. A couple quick sprays to the soil of each plant eliminates them for the entire winter that I have them indoors, and it will stop a very bad infestation within days.
If you use any biological/natural control like Bt, then you don't want to use any poison at all like sytemics or like a cleaner concentrate. Even if it has "Green" in it's name, it is still working as a poison and will cause the Bt to not work.
Bt is very simple, quick, easy, and completely natural. :)
- Tom

Yes the BT in water is the only thing I have found that works. Its a pain for me to hand water every plant but more of a pain to repot everything and I have opened new bags of soil to find the dang things already in there so didn't waste my time using it. The mosquito dunks work but will look for a liquid form of it. Thanks for the idea.

If I have a bad infestation Bt doesn't do it for me. I've had better luck repotting in a new sterile potting medium after soaking the roots. I do use Bt laced water on all my indoor/greenhouse seed trays even if I don't see any sign of gnats. They'll eventually appear. Any chemical or even hydrogen peroxide will kill off the Bt.

Karyn in my experience if you have a bad infestation in one plant, then you also have those little nasties in all your plants. So I'm curious if you repot everything? Sounds like a lot of work. Wouldn't it be easier just to lay off the chemicals & poison for a little while?
Btw, I should mention that it's importantant to actally get Bti, Bacillus thuringiensis israelensis. It's different than the common strain used for vegetable gardens & caterpillers. You want the one that is specifically for mosquitos or it just won't work very well.
- Tom

I hate to be the bearer of bad news, but fungus gnats usually don't cause leaves to fall off. Sounds like you probably have spider mites too.

Tom I keep all the cuttings and seed trays separate from mature plants. I treat everything nearby but only repot cuttings. Seed trays are watered with Bt whether they show signs of gnat infestation or not. If a tray of cuttings has a heavy infestation I repot, otherwise I just use the laced water. I posted previously about the different strains of Bt.

As far as chemical controls I only use them when absolutely necessary and then only things like homemade preps containing alcohol, soap and now this Simple Green, never systemics. I've also used Neem which I don't think works well at all, Bt obviously. I also use miticides on Broad mites only, Forbid and Floramite. Spider mites can be tken care of with water.