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Hydrilla (Hydrilla verticiilata) 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 preand 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 preand 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 (x= 2864. SE = 304) did not differ from after treatment counts x = 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. [ABSTRACT FROM AUTHOR]

Fluridone was applied to a 98-8-ha lake in Orange County, Florida, USA, in five different treatment plots between October 1982 and February 1983 to control a severe infestation of Hydrilla verticillata. Hydrosoil residues and submersed aquatic plant biomass were monitored within the lake. Fluridone did not affect the submersed vegetation during the 4-month fall-winter treatment period. As water temperatures increased during spring, Hydrilla biomass declined at an average of 0.178 kg m−2 per month. By summer (192 days after last treatment), the target species could not be found within the lake. Fluridone residues were detected in the hydrosoil immediately following treatments and generally peaked coinciding with the decline in aquatic plant biomass. The maximum fluridone detected in the hydrosoil was only 5% of the 2.25 kg ha−1 applied, and this amount was obtained from outside of a treatment area. Residue concentrations were highly variable between sampling sites and sampling periods and unexpectedly increased 14 months after treatment. Winter-killed marginal vegetation is a possible source of this increase. Detectable concentrations of fluridone, and vegetation control, persisted for a total of 86 weeks from the date of the last treatment and non-detectable residues may have persisted after 86 weeks. This study indicates that a lower application rate might have provided adequate control of Hydrilla and possibly decreased residue concentrations in non-target areas. [ABSTRACT FROM AUTHOR]