Used by professionals for more that a decade, Mosquito Dunks have proven their value in destroying Mosquitoes - by killing the larvae before they mature into biting adult pests. Dunks, along with BTI Briquets, are the only sustained-release BTI mosquito larvicides available. Once a month float a Dunk in the Water Garden and every place water accumulates around your home - you'll be rid of mosquitoes for the whole season. Each Dunk will effectively treat up to 100 square feet of surface water regardless of depth. Dunks may be broken to treat small areas. Unused and dried out Dunks retain their potency indefinitely.