Laserfiche WebLink
Trlclopyr for selective whole -bay milfoil management <br />Table 4. Following large-scale triclopyr treatments of St. Albans, Gideons, and Grays Bay, the % Eurasian watermil loll (EWM) frequency, <br />% mvasnre EWM biomass, % native plants biomass, % native plant frequency, mean number of native We per point, % area covered with <br />plants, and % submersed plant biovolume along 9 transects (via hydroacousttcs) were recorded during June and August from 2011 to <br />2013 <br />Year <br />Month <br />Trmt Date <br />% EWM <br />Fre- <br />quency <br />% EWM <br />Biomass <br />% Native <br />Biomass <br />% Native <br />Plant Fre- <br />quency <br />Mean <br />Native . <br />Tbxa Per <br />Point <br />% Area <br />Covered % Plant <br />with Blovol- <br />Plants ume <br />(f95% Cl) (f95% Ci) <br />SL Albans Bay <br />46 <br />54 <br />90 <br />3.2 <br />81(8) <br />60 (6) <br />2012 Jun 25 May ` ' <br />88 <br />64 <br />2011 <br />Jun <br />26 May <br />54 <br />30 <br />68 <br />80 <br />1.9 <br />81(9) <br />25 (5) <br />3.2 <br />Aug <br />41(6) <br />0 <br />0 <br />100 <br />93 <br />3 <br />85 (7) <br />40 (6) <br />2012 <br />Jun <br />31 <br />12 <br />4 <br />96 <br />91 <br />2.6 <br />91(6) <br />77 (6) <br />Aug <br />38 <br />3 <br />97 <br />90 <br />2.4 <br />84 (8) <br />61(5) <br />2013 <br />Jun <br />14 Jun <br />55 <br />10 <br />90 <br />91 <br />35 <br />87 (5) <br />51(7) <br />Aug <br />1 <br />0 <br />100 <br />93 <br />3.3 <br />86(g) <br />53 (5) <br />Gideons Bay <br />2011 <br />Jun <br />9 Jun <br />49 <br />24 <br />73 <br />90 <br />2.3 <br />80 (7) <br />30 (4) <br />Aug <br />5 <br />1 <br />99 <br />89 <br />2.8 <br />85 (9) <br />42 (4) <br />2012 <br />Jun <br />* <br />31 <br />8 <br />91 <br />89 <br />2.5 <br />91(9) <br />72 (8) <br />Aug <br />44 <br />a <br />92 <br />94 <br />33 <br />88 (11) <br />67 (7) <br />2013 <br />Jun <br />11 <br />8 <br />92 <br />91 <br />2.5 <br />85 (6) <br />38 (5) <br />Aug <br />29 <br />5 <br />95 <br />92 <br />3.4 <br />94 (4) <br />67 (7) <br />Grays Bay <br />2011 Jun <br />56 <br />27 <br />73 <br />86 <br />2 <br />70 (7) <br />37 (4) <br />Aug <br />90 <br />46 <br />54 <br />90 <br />3.2 <br />81(8) <br />60 (6) <br />2012 Jun 25 May ` ' <br />88 <br />64 <br />36 <br />90 <br />2.4 <br />87 (5) <br />73 (7) <br />Aug <br />16 <br />2 <br />98 <br />89 <br />3.2 <br />76 (8) <br />41(6) <br />2013 Jun <br />3 <br />15 <br />85 <br />87 <br />3.1 <br />81(6) <br />50(7) <br />Aug <br />31 <br />1 <br />99 <br />90 <br />3.1 <br />87 (7) <br />64 (4) <br />`A reduced scale heat awe dM ha al 750 µglL bidepyr (a 7996 ndochon M Uarbecrde um compered to 2011) was epptud on 22 June 2012 on d 3mm EWM Ueda that <br />began W recover m late 2011 <br />waterWdy. The treatment in 2011 was applied at higher <br />rates to a series of both large and small blocks as well as <br />small narrow shoreline strips (Fig. 2). Triclopyr concentra- <br />tions in the treatment blocks were -5-15 tunes below the <br />target concentration of 1500 AgIL throughout the sampling <br />period (Fig. 4). Although this may be partially attributed to <br />the extended release of product (-X12-36 h) from a granular <br />herbicide, rapid dispersion of triclopyr across the large bay <br />was observed within 1 day of application. Triclopyr con- <br />centrations in untreated sample sites in the middle of the <br />large bay were similar to many of the targeted treatment <br />sites by 1 day after treatment (DAT) suggesting a bay -wide <br />exposure to low concentration of triclopyr. As noted for <br />St. Albans Bay, the presence of a thermocline at —6 in <br />prevented deep -water mixing of the triclopyr in these open <br />water sites. Given the confounding issues with initial tn- <br />clopyr behavior in this large open bay, triclopyr half=hves <br />were determined based on data collected from day 2 to day <br />10. We calculated an average half-life of 3.7 d in the areas <br />where the large -blocks were treated (Fig. 4) and an average <br />half -fife of 9.4 din untreated open water areas (Fig. 4). AI - <br />though the total days of exposure to triclopyr in this large <br />open bay were unexpectedly similar to that calculated for the <br />closed bays, a key difference was that the other bays reached <br />equilibrium around 300 µg(L triclopyr whereas Gideons <br />reached equilibrium closer to 100 lig/L. The presence of a <br />thermocline was important in maintaming an extended ex- <br />posure to low concentrations of triclopyr in Gideon Bay. <br />Although there was no stated objective for providing ex- <br />tended exposures to lower concentrations of triclopyr in <br />Gideon Bay, the data demonstrated this was essentially the <br />outcome of the application. <br />A significant decline in EWM frequency occurred from June <br />to August 2011 (49 to 5%) following the whole -bay treat- <br />ment (Table 6). A subsequent sampling event in September <br />2011 showed that EWM frequency had increased to 18%, <br />suggesting a late season recovery. This recovery was promi, <br />neat in areas where the dense beds of EWM had been previ- <br />ously detected in June 2011. EWM frequency increased to <br />31 and 44% in June and August 2012, respectively, despite <br />an additional June 2012 triclopyr treatment, For both 2012 <br />315 <br />