Gnatrol is a highly selective, biological larvicide for use in greenhouses to control fungus gnat larvae. It may be used on a wide variety of ornamentals, as well as all bulb crops, bedding plants and vegetable sets. Once the larvae have ingested Gnatrol, they become paralyzed, stop feeding immediately and die—usually within 24 hours. Gnatrol is now available in a water dispersible granule (WDG) formulation that has a 2 year shelf life and will not leave a residue. It is also much easier to measure for increased application accuracy. Light, Medium or Heavy depending on if you are using it as a preventative or for a light to heavy infestation.