Mosquito Dunks are a foundational tool for biological water management. Using Bacillus thuringiensis israelensis (Bti) embedded in a slow-release cork-matrix, these units are designed to provide a 30-day release cycle in stagnant water. This method allows you to manage mosquito populations at the larval stage with minimal impact on other wildlife, fish, or pets.
Buoyancy & Structural Realities
The "Dunk" is a mechanical delivery system that uses a buoyant fibrous material—primarily compressed cork—to stay at the surface. This ensures the biological agent remains in the upper few inches of the water column, which is the primary feeding zone for larvae. A practical reality of this organic construction is that once the unit is about 75% degraded, it can fragment into smaller pieces. These fragments may wash away more easily than a whole unit, so replacing the dunk every 30 days is key for consistent results.
Because these units are lightweight, they can be swept away in high-flow areas like rain barrels or gutters during heavy rain. A practical engineering fix is to anchor the unit using a weighted fishing line or zip-tie through the center hole. It is also important to manage expectations: this is not an "instant-kill" product for adults, but a proactive tool to prevent the next generation of pests from maturing.
- Biological agent is specific to mosquitoes, fungus gnats, and blackflies.
- Maintains surface tension buoyancy to maximize larval ingestion.
- Dry-pressed mold keeps the biological spores viable for up to two years.
For a different delivery style that dissolves completely without leaving a cork residue, you might consider the Terro water-soluble pouches.
Check out the full selection of biological larvicides and water maintenance products in our mosquito larvicide dunks section.
