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Assessment of uncontained Zequanox applications for zebra mussel control in a Midwestern lake

December 22, 2019

Zebra mussels (Dreissena polymorpha) are invasive bivalves that have perturbed aquatic ecosystems within North America since their introduction in the mid-1980s. Control of zebra mussels has largely been restricted to raw water conveyance systems and associated infrastructures because few control products are registered for application in surface waters. The biopesticide Zequanox was registered in 2014 by the U.S. Environmental Protection Agency for controlling dreissenid mussels (zebra and quagga mussels (Dreissena rostriformis bugensis) in surface waters. Previous Zequanox applications in surface waters have used vertical impermeable-membrane barriers to contain treated water. Studies have indicated that uncontained applications may be successful if Zequanox suspensions of the correct viscosity are applied to facilitate the creation of stratified benthic treatment layer. In this study, Zequanox was applied to replicate 0.30-hectare plots within a small inland lake using a custom-engineered, boat-mounted application system to determine if uncontained Zequanox applications could be used to manage zebra mussel populations and to protect native unionid mussels within zebra mussel infested waters. To determine success, the following specific objectives were investigated during, 30 days after, and/or 1 year after Zequanox exposure: (1) evaluate Zequanox concentrations during exposure; (2) monitor water quality during and after exposure; (3) evaluate the mortality of zebra mussels that were caged within treatment zones during the exposures; (4) evaluate the densities of naturally occurring zebra mussels with treatment zones before and after Zequanox exposure; and (5) evaluate the survival, condition, and dreissenid infestation of native mussels in the treatment zones before and after Zequanox exposure. Zequanox rapidly dissipated from the treated plots, resulting in no appreciable treatment-related mortality of zebra mussels and insignificant impacts to water quality. Zequanox exposure-related impacts to native mussels were not observed.