Knock-Out Gnats Granules A biological larvicide that kills fungus gnat larvae. Active ingredient Bacillus thuringiensis (Bt). Bt has been proven effective for the control of fungus gnats. Plant-safe, environmentally responsible choice for houseplant growers and home greenhouses. Water-dispersible Bt granules are easy and convenient to use. 4 oz. makes up to 96 gallons of solution.