Kurt D. Getsinger

Whole Lake Fluridone Treatments For Selective Control of Eurasian Watermilfoil: II. Impacts on Submersed Plant Communities

ABSTRACT The aquatic herbicide fluridone is being used in northern tier states to selectively control the submersed exotic species Eurasian watermilfoil (Myriophyllum spicatum L.) growing in lakes and reservoirs. Reliable quantitative information linking changes in the submersed plant community following fluridone applications is limited, particularly with respect to water residue records. Therefore, a study was conducted to investigate the effect of low-dose fluridone treatments on the submersed plant communities in four lakes in Michigan. The overall study objective was to determine whether submersed plant species diversity and frequency were impacted by low-dose fluridone applications in the year of treatment, when targeting a whole lake for Eurasian watermilfoil control. The primary objectives of this portion (part II) of the overall study was to determine fluridone effectiveness on the exotic submersed species Eurasian watermilfoil (Myriophyllum spicatum L.) and to evaluate shifts in plant species diversity at one year posttreatment. Secondary objectives included determining fluridone effectiveness on the exotic submersed species curlyleaf pondweed (Potamogeton crispus L.) and verifying laboratory-derived results of fluridone concentration and exposure time relationships with respect to efficacy against Eurasian watermilfoil. Quantitative sampling of vegetation was performed using point-based frequency of species occurrence to evaluate whole-lake distribution and diversity of the submersed plant community of all eight study lakes. The technique was implemented using global positioning and geographic information systems, with a minimum grid resolution of 50 m by 50 m. Plant surveys were conducted in early to mid May and in mid August in 1997 (year of treatment) and 1998 (12 and 15 months post treatment). The fluridone concentration and exposure time (CET) relationship resulted in good to excellent control of Eurasian watermilfoil through 15 months posttreatment on three of the treated lakes (Big Crooked, Camp, and Lobdell). On a fourth lake, Wolverine, the required CET relationship was not maintained and poor control of Eurasian water milfoil was observed. There was no strong evidence of long-term curlyleaf pondweed control in any of the fluridone-treated lakes. The herbicide application strategy used in this study did not significantly impact the native plant species diversity or cover in the year of treatment, or through 15 months posttreatment, in any of the fluridone-treated lakes. Native plant cover was maintained at levels >70% in the year of treatment and at one year posttreatment; a level above the range (20 to 40%) recommended for healthy fish and wildlife habitat. The selective control of Eurasian watermilfoil achieved in this study verified results from previously conducted laboratory and outdoor mesocosm evaluations.

Small-Plot, Low-Dose Treatments of Triclopyr for Selective Control of Eurasian Watermilfoil

ABSTRACT Small-plot treatments of triclopyr were conducted on Lake Minnetonka and Lake Minnewashta, MN, during June 1998 to investigate the herbicides potential to selectively control Eurasian watermilfoil (Myriophyllum spicatum L.) at low doses. Applications were made on 1-ha plots with rates based on plot type: references (0 mg acid equivalent (ae)·L−1), protected plots (0.5 mg ae·L−1), semi-protected plots(1.0 mgae·L−1), and unprotected plots (1.5 mgae·L−1). Plot protection was a function of potential mixing in the water column. Herbicide residues were monitored to determine dissipation 1 through 72 h post treatment. Samples were analyzed with both a high performance liquid chromatography technique and an enzyme-linked immunosorbent assay method. Results from these two analytical techniques were compared, and found equivalent (R2 = 0.96). Triclopyr had a relatively short half-life for each treatment (3.5 hr at 0.5 mg ae·L−1, 2.9 hr at 1.0 mg ae·L−1, and 4.2 hr at 1.5 mg ae·L−1). At 8 weeks post treatment, there was a 30 to 45% reduction in Eurasian watermilfoil distribution. Greatest Eurasian watermilfoil control was achieved in plots using higher triclopyr rates. Frequency of native plants decreased by 24% in the untreated reference plot, 20% in the 0.5 mg ae·L−1 plot and 6% in the 1.0 and 1.5 mg ae·L−1 plots. Mean species per point, however, either increased or remained unchanged in seven of the nine treated plots. Decline of native plants may be partially attributed to the onset of fall senescence. Larger contiguous areas, higher triclopyr rates, and sequential applications may be required to enhance Eurasian watermilfoil control in small-plot, partial lake treatments.

Whole Lake Fluridone Treatments For Selective Control of Eurasian Watermilfoil: I. Application Strategy and Herbicide Residues

ABSTRACT The herbicide fluridone is being used in northern lakes and reservoirs to control the exotic species Eurasian watermilfoil (Myriophyllumspicatum L.). Since quantitative information linking changes in plant communities following fluridone applications is limited, particularly with respect to water residue records, a study was conducted to investigate the effect of low-dose treatments on the submersed plant communities in four Michigan lakes. The overall study objective was to determine whether plant species diversity and frequency of occurrence were affected by low-dose fluridone applications in the year of treatment. The primary objective of this portion of the overall study was to provide an application strategy that would maintain a threshold dose of fluridone, 5 μg·L−1 declining to 2 μg·L−1, in the treated lakes to selectively control Eurasian watermilfoil. Study lakes were 55 to 220 ha in size and contained an average of nine species of submersed plants. Big Crooked, Camp, Lobdell, and Wolverine lakes were treated in mid-May 1997 with the formulation Sonar® AS, to yield an initial concentration of 5 μg·L−1 fluridone in the upper 3.05 m of each lake. Asequential application of Sonar® AS was conducted on each lake at 16 to 21 days after initial treatment (DAIT), intended to reestablish a fluridone concentration of 5 μg·L−1 in the upper 3.05 m of each lake. Bass, Big Seven, Clear, and Heron lakes received no fluridone applications and served as untreated reference sites. Water residue samples were collected at prescribed intervals on each fluridone-treated lake from pretreatment up to 81 DAIT. Samples were collected from six littoral stations and from two deep locations throughout each lake, and temperature profiles were measured at the deep stations. Fluridone residues were analyzed using two separate techniques, the newly developed enzyme-linked immunosorbent assay and the standard high performance liquid chromatography method. Fluridone levels on three of the treated lakes met the laboratory-derived criteria for achieving good control of Eurasian watermilfoil by providing a peak concentration of approximately 5 μg·L−1 during the first 2 weeks posttreatment, and by main taininga concentration >2 μg·L−1 through 60 DAIT. Residues became well mixed in the water column under isothermal conditions, and thermal stratification prevented mixing of fluridone into deeper and colder waters. Residue data indicated that thermal stratification, or the lack thereof, at the time of herbicide application can affect target herbicide concentrations. Using the volume of a pre-selected depth zones to calculate the amount of fluridone needed to achieve a particular target concentration can result in an over- or under-dosing of a water body.

Comparison of Immunoassay and HPLC for Analyzing Fluridone Concentrations: New Applications for Immunoassay Techniques

ABSTRACT High performance liquid chromatography (HPLC) and an enzyme-linked immunosorbent assay (ELISA) technique were used to analyze concentrations of the aquatic herbicide fluridone (l-methyl-3 phenyl-5-[-3 (trifluromethyl) phenyl]-4 (IH) pyridinone) in 488 surface water samples collected from two lakes in Michigan treated in 1997, 2 Michigan lakes treated in 1998, 1 lake in Florida treated in 1996, and a series of research ponds treated in Florida in 1997. Samples were collected following application of fluridone associated with operational treatment programs that targeted the exotic submersed plants Myriophyllum spicatum L. (Michigan) and Hydrilla verticillata (L.f) Royle (Florida). ELISA and HPLC results compared well (r2 = 0.84 to 0.98) across a broad range of initial fluridone treatment rates (5 to 150 μg L−1). The potential use of ELISA to monitor fluridone residues in the water in near real-time, and to use this residue data for lake specific herbicide treatment recommendations represents a unique use of ELISA technology.

Aquatic Plant Communities in Waneta Lake and Lamoka Lake, New York

Abstract A point-intercept survey was implemented in August 2000 to determine the distribution and richness of aquatic plant species present in Waneta Lake and Lamoka Lake, NY. Myriophyllum spicatum (Eurasian watermilfoil) was the most commonly observed species in Waneta Lake (25% of entire lake, 78% of littoral zone) and Lamoka Lake (43% of entire lake, 77% of littoral zone). Eurasian watermilfoil biomass (24.3 g DW/m2) was also significantly greater (p ≤ 0.001) in Waneta Lake than native plant biomass. Our data suggests that Eurasian watermilfoil is invading the native plant communities of Waneta Lake and Lamoka Lake, thereby displacing native plants and limiting their growth to the shallow waters of the littoral zone.

Evaluation of Transparency and Light Attenuation by Aquashade

ABSTRACT Aquashade™, a colorant and dye registered by the US Environmental Protection Agency (USEPA) for use in aquatic environments to manage plant growth, does not reduce the visibility of water that otherwise would meet safe swimmming standards. This product was examined for its potential impact on underwater visibility in surface waters used for recreational swimming. Aquashade™ treatments of 0, 1, and 5 mg L−1 were evaluated in 3-m deep outdoor tanks containing reservoir water. Transparency and light attenuation were examined using a Secchi disk and an underwater photo synthetically active radiation (PAR) meter. In the first experiment, filtered lake water was used, while in the second, bentonite clay was added to provide a light transparency of approximately 1 m. In filtered lake water, Aquashade™ treatments (1 mg L−1 and 5 mg L−1) reduced light transparency by approximately 10% and 30%, respectively, but the transparency (272 and 194 cm, respectively) was well above typical international (100 cm) a...

Concentration–Exposure Time Relationships for Controlling Sago Pondweed (Stuckenia pectinata) with Endothall

The submersed macrophyte, sago pondweed, frequently grows to nuisance levels in water conveyance systems throughout the western United States and can cause problems in lakes, reservoirs, and other water bodies. The liquid dipotassium and dimethylalkylamine salt formulations of endothall were evaluated for controlling sago pondweed using short exposure times (3 to 24 h) under controlled environmental conditions (14 : 10 h light : dark; 21.5 C). Endothall treatments ranged from 1 to 10 mg ai/L (dipotassium salt) and 0.5 to 5 mg ae/L (dimethylalkylamine salt). Sixteen concentration and exposure time (CET) combinations were evaluated in each study. At 4 wk after treatment, all CET combinations significantly reduced shoot biomass (43 to 99%) of sago pondweed compared with the untreated reference. Reduction in shoot biomass was greater in plants that received higher herbicide doses and longer exposure times. In addition, more than half of the endothall CET combinations controlled sago pondweed by at least 90%, with some providing > 98% control. At the endothall CETs evaluated, regrowth of sago pondweed could occur after 4 wk, and some level of retreatment might be required to maintain plant control throughout the growing season. Results indicate that endothall shows promise as an alternative vegetation management tool in flowing-water environments. Nomenclature: Endothall, sago pondweed, Stuckenia pectinata (L.) Boerner PTMPE