What are you attempting to control? Dunks are usually just placed in the body of water you are intending to control the mosquito larvae in.

Sorry, I forgot to mention I am wanting to use this to control gnats in the plant soil of my outdoor containers. I read that you use Bacillus. I'm sure these are not shore flys but fungus gnats that came in a plant I ordered thru a catalogue compnay :(

Phoebe, I use about a quarter size chunk of dunk...hey I like the way that sounds... in a 2 gallon bucket. After It's been in there overnight or for a few hours, I pour about 2 quarts in a watering can, but leave the chunk in the bucket. Then I add more water to the bucket. This way the Bacillus lasts for a long time. I have been using this indoors for fungus gnats and it has been very effective. It did take a few days though. Also, keep using it for a little while after the gnats are gone to be sure you get all the larvae. Lisa

Dunks are for skeeters

Gnatrol is a Bt made for fungus gnats

Bacillus thuringiensis israelensis is the same active ingredient in Gnatrol and mosquito dunks. For heavy fungus gnat infestations you may need to re-apply two or three times at 5 day intervals. Bt only targets the immature stages and the adults live around 3 weeks. The best solution though is non-chemical: keep the soil as dry as horticulturally possible with infrequent, deep watering if the plants can stand it.

"The best solution though is non-chemical"

Bt is non-chemical. Your point on cultural methods is valid, however.

It's probably a matter of semantics and gets into a gray area where people have isolated and identified the active ingredient from a natural source. The delta endotoxin is naturally produced from a bacterial source. I also consider Spinosad (derived from another bacterial soil dweller) to be chemical, though it too naturally-derived. I don't think that there's much debate about rotenone, pyrethrum, or nicotine as being chemicals despite their natural origin.