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

• Published in: Lake and reservoir management Vol. 18; no. 3; pp. 191 - 200
• Main Authors: Madsen, John D., Getsinger, Kurt D., Stewart, R. Michael, Owens, Chetta S.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.09.2002
• Subjects: aquatic plant control; invasive species; low-dose herbicide; non-target plants; Sonar AS
• ISSN: 1040-2381; 2151-5530
• DOI: 10.1080/07438140209354148

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.