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

• Published in: Lake and reservoir management Vol. 18; no. 3; pp. 181 - 190
• Main Authors: Getsinger, Kurt D., Madsen, John D., Koschnick, Tyler J., Netherland, Michael D.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.09.2002
• Subjects: aquatic plant control; invasive species; low-dose herbicide; Sonar AS
• ISSN: 1040-2381; 2151-5530
• DOI: 10.1080/07438140209354147

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.