Effects of temperature on mortality of quagga mussels (Dreissena bugensis) exposed to potassium chloride and copper-based molluscicides in high conductivity waters

Dreissenid mussels (quagga and zebra mussels, Dreissena bugensis and polymorpha) continue to spread throughout inland waterbodies of North America. Although there are considerable management and mitigation efforts underway to prevent infestation of new waterbodies, there have been relatively few successful efforts to eradicate mussels once detected due to a lack of cost-effective treatments. Two potentially cost-effective molluscicidal agents, potassium chloride (KCl, also called muriate of potash) and copper (formulated as Earthtec QZ®), have successfully treated infested waters, but have varying efficacy under different water quality and temperature conditions, and to date have only been applied in moderate conductivity waters (defined here as < 400 µS/cm) common throughout North America. Natural resource managers need information on the efficacy of these chemicals in high conductivity waters more typical of riverine systems and arid climates, in addition to the range of water temperatures typically encountered in the field. We evaluated the dose-response of quagga mussels to KCl and Earthtec QZ® in high conductivity water (≈ 700-1,400 µS/cm) across a range of temperatures (10, 18, 22 °C) to determine appropriate doses and treatment duration resulting in 100% mortality. Our data indicate that treatments in cool temperatures (i.e., 10 °C) may be challenging for eradication efforts in high conductivity waters because none of the KC1 treatments and only one copper treatment resulted in 100% mortality within the experimental period. However, both KC1 (> 200 ppm) and copper (120 and 180 ppb) were consistently able to induce 100% mortality in quagga mussels in warmer temperatures (i.e., ≥18 °C) and thus may be good candidates for field scale application in high conductivity waters. The results of this study indicate that field-scale application should strongly consider environmental conditions during the period of application when selecting dosages and treatment duration.