Hydrilla Management in Piedmont Reservoirs Using Herbicides and Triploid Grass Carp: A Case Study

We developed a three‐step management strategy for hydrilla Hydrilla verticillata in five Piedmont reservoirs operated by Duke Energy Corporation. This strategy involves (1) early detection of hydrilla, (2) use of registered herbicides for plant suppression along with stocking 20 triploid Grass Carp Ctenopharyngodon idella per surface acre of infestation, and (3) maintenance stocking of triploid Grass Carp to prevent hydrilla regrowth from tubers. Following this strategy, hydrilla in the water column was eliminated within one calendar year after Grass Carp introduction in four out of five reservoirs. This suggests that integrating herbicide applications with stocking Grass Carp largely eliminates the multiyear lag effect normally associated with using Grass Carp alone. A maintenance density of at least one triploid Grass Carp per eight surface acres of the reservoir prevented hydrilla regrowth except for a brief and minor reinfestation in one of five study reservoirs. This management approach proved successful when hydrilla coverage was as little as 1–3% of the reservoir's surface area. Detecting and controlling hydrilla early during the infestation should reduce the cost of management and perhaps minimize some adverse effects associated with the introduction and use of triploid Grass Carp. Received November 14, 2012; accepted January 15, 2013