BTi (Bacillus thuringiensis israelensis). Sold in the form of Gnatrol (the brand I keep on hand), Knock Out Gnats, others. In a pinch, you can buy mosquito dunks - have the same BTi as active ingredient - float a dunk in a container of water over night, then use that water to water on your normal schedule. A naturally occurring bacterium, its safe for you, your kids, your pets.

Be patient. It can take using it at least three consecutive weeks before the breeding cycle is broken and gnats are gone (kills the larvae, not the adults).

Thanks - I have some I used this summer to control tomato hornworms.

The BT (probably 'kurstaki')for caterpillars isn't the same one that is effective for mosquito and gnat larvae, your hornworm product won't help you.

The one you want is specifically Bacillus thuringiensis subspecies israelensis for gnat control, BTi.

Success!! The BT I have for Hornworms worked immediately. I know I will have to give it a second drench for the eggs in the soil, but I guess the little knats didn't know my BT was for larger critters!

OK, hope you are right and its done the trick, but do you know how BT works? It must be eaten by insects or the larvae to be effective and works by interfering with digestion - in other words, after ingesting some, they stop eating and starve, would usually take more than a day.

It won't affect eggs, it would only kill the larvae if they ate it....

The normal course for gnats is use as a soil drench each time you water on your normal watering schedule for no less than three consecutive weeks to break the breeding cycle - adult, to egg, to larvae which then becomes adult to lay more eggs.

I use this stuff, works great.

Karen

Here is a link that might be useful: insecticide

Since the life of a knat is 7 days, I figure I will drench the soil a couple more times to be sure I got all the little buggers.

Thanks for the input!