I've very successfully gotten rid of fungus gnats on house plants using mosquito dunks which have the right kind of BT in them to kill the larva in the soil. I just dropped the dunks in my watering can.
The question here is whether mosquito dunks are entirely safe for humans. The BT part itself is safe:
Bacillus thuringiensis
Mosquito dunked water is safe for pets and fish (I use them all summer in the ponds).
So, I wonder if Knock Out Gnats from Garden's Alive uses BT in a carrier that is safe for humans, or if one of the products listed for BT Israelensis on the above linked site is for safe for use on vegetables.

Looks like Gnatrol is recommened for vegetables with fungus gnats:
CONTROLS FOR GREENHOUSE VEGETABLE INSECT PESTS

Bonnie, I was in at the garden center the other day and asked about fungus gnats. The guy said Bt israelensis but he didn't have any spray in stock . . .

So, I went out the door with yellow sticky traps. Forgot the price but they were really cheap and now every plant in the house has a trap. The gnats immediately stopped appearing in front of the TV screen, flying millimeters from the end of my nose, crashing into my glasses, etc.

If this continues, I'm going to be happy and it will beat the heck out of carrying 'em out on the deck 2 or 3 times every Winter and spraying 'em with organic bug killer. That didnÂt work all that well, anyway.

digitS'

Mosquito Bt and fungus gnat Bt is the same Bt. I also was down at the local garden shoppe getting a few more dunks as they are around my house plants as well.

In the greenhouse, when I start seedlings off, I have 6 x 5 gal buckets that I fill with water, let sit 24 hours for the chlorine to gas off, and then plonk a dunk in each one. I use that water to initially water in all the seedlings, and I have no fungus gnats.

I'm afraid I'm more confused than before. So is Gnatrol and Knock Out Gnats the same chemical? If so, why do they say it's for ornamental use only?

Bonnie

I'm not sure if what I have are fungus gnats or not, but they are sure annoying. They are not on my plants, however, but hang around in the kitchen or wherever they can annoy me, especially around food. Anyway, I read of a natural, nontoxic way to get rid of them and it does work for me. You pour apple cider vinegar in a small cup or dish, mix a little detergent in it, cover with plastic wrap, poke some holes with a toothpick, making one a little bigger. The gnats will eventually (fairly soon) get in the dish, I guess through the larger hole, and can't get out, so you will see them lying on the bottom. Hope it works for some of you.

I got rid of mine and no more came in until we had that 70 degree weather last Monday, so I had to put another dish out.

Just a quick comment. You can get rid of almost all fungus gnats on house plants by just leaving the surface of the soil dry out completely before watering the next time (at least an inch or more down into the pot). The only place they can live and reproduce is in the surface of moist/wet soil. When I occasionally have a problem with them, I usually just realize IÂve been keeping something too wetÂwhich I occasionally need to do because of my weird scheduleÂand when IÂm able to start letting them dry adequately again, they go away all by themselves. IÂve never used any chemicals. This year IÂve got a Brugmansia inside that IÂm keeping in a saucer of water so it doesnÂt die while IÂm gone, and two sweet potato plants I decided to keep inside over winter that IÂm keeping VERY wetÂfor the same reason, and IÂve got my fingers crossed that I donÂt develop a problem.

You might want to try the leave-em-dry method, Bonnie, and maybe you wonÂt need to use any chemicals at all.

Skybird

Shady Garden, those sound like fruit flies, not fungus gnats.

Skybird, the dry soil top method keeps them in check, but they're still there as eggs or some dormant thing, and once the soil gets wet, they're baaaaaaaak.

For established house plants, they're more a nuisance than anything, right now there are half a dozen fluttering around the front of my computer screen; they reside in the large potted vine that sits to the right of the desk.

For nursery and seedlings, its a major issue. The larvae snarf the tiny root hairs, and if this is a single rootlet seedling, they'll knock back the plant growth considerably, and can kill the plant.

Bt is a bacteria, not a chemical, and considered an organic treatment. Once established in the soil, it seems to last a long time.

I'd like to try Shady's idea for the fruit flies . . . just about peach season and then for however long it takes!

digitS'

Skybird, I'm pretty sure I'm already using the keep it dry method (not so much on purpose, but just out of pure neglect, LOL), and I have to agree with David, those eggs will sit dormant in the soil until it gets watered, and then you have a whole 'nother batch to deal with.

Digit, the sticky traps are another "keep 'em in check" method, but it doesn't eliminate them either.

Maybe I will use the Knock out gnats on the houseplants and just put the sticky traps in the herb pots, since I'm not 100% sure it's safe for edibles. Thanks everyone for the suggestions.

Bonnie

do gnats eat cabbage leaves?
i am trying to help my grandbaby grow a cabbage for her school project. it was in the sunroom until today . i moved it outside and covered it with a frost cover.
i think they are gnats , tiny black bugs that fly.bugs in the soil. i dont see anything else around it, but something is eating the leaves.
i am going to try the peppermint tea remedy.
also, does anybody know how long it takes for a cabbage to grow a head ? lol
it has about 15 big leaves all sprouted out, but its ben growing from a tiny transplant she brought home in february. think its the flat head one.
thanks.
kate1948

Kate1948, fungus gnats eat fungus on the soil surface and plant roots. I don't think they eat leaves.

Black bugs on the soil that fly (they also JUMP! but I guess they've got wings as well) AND eat plant leaves may be flea beetles. They produce "shot holes" and are especially troublesome in cabbage-family plants.

If these bugs are actually flying around your cabbage - they probably aren't flea beetles. Flea beetles don't really "cruise" the garden or "hover."

Flea beetles often spend their time in soil cracks and beneath debris, so they are a little hard to kill. I use Rotenone/Pyrethrin spray and make sure to spray the soil around the plants.

Right now, I've got bok choy transplants that are just getting beaten down to nothing. If I don't spray soon, they'll never be able to get started growing.

digitS'

Here is a link that might be useful: flea beetles

I used a combination of the yellow sticky traps and this real cool bug zapper I bought. It looks like a small tennis racket, but you put batteries in it and press two buttons on the handle and that electrifies the grid and zaps any bugs you hit with the racket.

Took care of the problem. I had two different sized flying gnats, so I think I had both fruit flies and fungus gnats.