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Trlclopyr for selective whole -bay milfoll management In addition to the plant data collected from 2011 to 2013 for this study, we reviewed plant frequency data collected in 2009 on St. Albans and Gideons bays by Blue Water Science (St. Paul, MN) using a similar point -intercept methodology, and 2010 frequency data on Grays Bay collected by the U.S. Army Engineer Research and Development Center us- ing the same point -intercept sampling grid. These data were not included in the analysis described above; however, they provided additional information on the pretreatment condi- tions experienced in late spring (Jun) and summer (Aug or Sep) on these bays during a year when no treatment was conducted_ Plant biomass samples were collected from 30 randomly se- lected survey points in each bay at depths <5 m using a rake sampling methodology (Johnson and Newman 2011). Sam- ples were sent to the University of Florida Center for Aquatic and Invasive Plants and sorted to species for weighing. Once sorted, plants were dried at 70 C for 72 h or more. In review- iug the variation associated with biomass data for individual species, we ultimately combined data from all species to determine if treatments impacted overall biomass. Biomass data over the 3 -year period are presented as mean values for the 30 sample sites f95% confidence intervals (Q}. We also separated total native and EWM biomass to determine the impact of management on EWM contribution to overall bay biomass. Hydroacoustic transects At the time this project was initiated, there were ongoing evaluations on the use of low-cost sonar units to deter- mine pretreatment and posttreatment conditions of percent area covered (PAC) and percent biovolume (BV) along tran- sects to assess efficacy of large-scale hydrilla management (Netherland and Jones 2012). This approach seemed well- suited to address stakeholder concerns regarding impacts of whole -bay treatments on overall abundance of submersed aquatic vegetation (SAV) snLakeMinnetonka. Prior to treat- ment in 2011, we established 9 transects in each bay (due to technical issues, we were only able to analyze 8 tran- sects on Gideons Bay) and collected data using a Lowrance HDS 5 recording fathometer (Lowrance HDS. Navico Inc., Tulsa, OK). Transects were established to intersect sites along the point -intercept grid map. Transects were not um - form in length and were chosen to reflect a variety of water depths and initial plant densities (Fig. 2). Hydroacoustic transect distances ranged from 207 to 995 m, averaging 376, 673, and 490 m for St. Albans, Grays, and Gideons bays, respectively The boat running speed was 4-6 mph, and data were collected at ^-15 pings/s Detailed guidelines for collection of SAV data along transects can be found at www.cibiobase.com (cibiobase, Navico, Inc., Minneapolis, MN). We uploaded the recorded sonar files to the cibiobase site to determine presence of SAV and height of vegetation in the water column. These values were used to determine the PAC and BV along each transect. These parameters can also be calculated using a manual process that allows the operator to download the hydroacoustic data into an Excel spreadsheet and choose random points along transects to determine presence or absence of vegetation and height of vegetation in the water column (Hoyer et al. 2008). This manual process proved labor intensive, and following com- parison of more than 75 transects analyzed manually ver- sus the cibiobase website (including multiple transects from Lake Minnetonka in 2011), the differences were neghgn- ble given the efficiencies of automated analysis. All subse- quent transects in 2012 and 2013 were analyzed using the cibiobase method. The distance between the bottom acoustic signature and top of the plant canopy was recorded as the plant height for each ping. Plant heights were averaged across all pings within a OPS coordinate point. Plant heights from pings within a coordinate point that averaged <5% of depth were consid- ered not vegetated to minimize false detechons by bottom detritus Any points that exceeded this 5% threshold were considered vegetated in percent area vegetation calculations. The minimum depth for vegetation detection was 0.73 m. For presentation of PAC and BV data, we determined the average PAC and BY i95% CI for the 9 transects collected within each bay in June and August 2011 to 2013 to de- termine if treatments resulted in an overall change in either submersed plant coverage or BV. Results Herbicide concentrations and plant frequency [chill St. Albans Bay Following both the 2011 and 2013 whole -bay treatments in St. Albans Bay, triclopyr half-lives of .11.5 and 12.6 d were measured (Fig. 3A and 3B). Despite use of a granular herbicide, there was rapid dissipation of tdclopyr through- out the epilimnion. Initial triclopyr concentrations following the 2011 application were 510 µg/L, —30%n higher than tar- ' get treatment concentrations. This high concentration was attributed to the presence of a thermocline that prevented ` triclopyr from moving into waters <5 m in depth (data not shown). Accounting for the presence of a thermochne prior to treatment in 2013 resulted in an 11% reduction in overall herbicide use; however, measured triclopyr concentrations of 230 µglL remained below the target concentration of 310 µg/L (Fig. 3B). 311