Hydrilla (Hydrilla verticillata) is an exotic, submergent plant that clogs waterways in the southeastern United States yet appears to be beneficial to migratory waterfowl. We studied the effects of hydrilla control on wintering waterfowl populations at Lake Seminole, GA. We applied fluridone (Sonar®) in a low-dose injection system starting May 2000 in the Spring Creek arm of the reservoir. We used aerial photography and ground-truthing methods to quantify coverage of vegetation types and open water pre- and post-treatment for the entire reservoir. We flew weekly aerial surveys to document waterfowl numbers and distribution across the reservoir between 1 November and 15 March during 1998-1999 and 2001-2002 for pre- and post-treatment estimates. Application of Sonar® in the Spring Creek arm reduced hydrilla coverage in the reservoir from approximately 35% to 24%. Average number of ducks per flight before treatment (mean = 2864, SE = 304) did not differ from after treatment counts (mean = 2774, SE = 273) for the reservoir. However, the distribution of ducks changed, with use decreasing 12% in Spring Creek arm. Distribution of ducks before and after treatment revealed that ducks selected hydrilla greater than its availability. Our results indicate that biologists in the Southeast can reduce coverage of hydrilla using Sonar® applied in a low-dose injection system; however, waterfowl distribution may change following treatment.

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