Assessing the effects of application time and temperature on the efficacy of hot-water sprays to mitigate fouling by Dreissena polymorpha (zebra mussels Pallas).

Dreissenid mussel (Dreissena polymorpha, Dreissena rostriformis bugensis) expansion into the Western US has renewed interest in hot-water spray mitigation of mussel fouling on boat hulls, trailers, and other equipment. However, the efficacy of hot-water sprays to mitigate dreissenid fouling has not been experimentally assessed. Emersed, adult D. polymorpha were exposed to low-pressure, hot-water sprays at 40, 50, 60, 70, and 80 degrees C for 1, 5, or 10 s. Sprays at > or = 60 degrees C for 10 s or 80 degrees C at > or = 5 s were 100% lethal. In contrast, 1-10 s exposures did not induce 100% mortality at < or = 50 degrees C. The results indicate that mitigation of D. polymorpha fouling, especially in areas protected from the hydraulic impacts of high-pressure sprays requires spray temperatures of > 80 degrees C applied for > 5 s or no less than 60 degrees C applied for > 10 s. Thus, presently recommended spray temperatures of > or = 60 degrees C may not be 100% effective unless applied for >10 s.