Whole lake fluridone treatments for selective control of Eurasian watermilfoil: II. Impacts on submersed plant communities

Published source details Madsen J.D., Getsinger K.D., Stewart R.M. & Owens C.S. (2002) Whole lake fluridone treatments for selective control of Eurasian watermilfoil: II. Impacts on submersed plant communities. Lake and Reservoir Management, 18, 191-200.
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Summary

Action: Use herbicide to control problematic plants

A replicated, controlled, before-and-after study in 1997–1998 of eight freshwater lakes invaded by Eurasian watermilfoil Myriophyllum spicatum in Michigan, USA (Madsen et al. 2002) found that applying herbicide had no clear effect the overall richness or abundance of submerged plants, despite reducing watermilfoil abundance. Comparing data from just before and 3–15 months after applying herbicide, watermilfoil frequency (percentage of survey points where present) declined in 9 of 12 comparisons in treated lakes (before: 39–73%; after: 0–13%) but increased or did not significantly change in 12 of 12 comparisons in untreated lakes (before: 30–43%; after: 33–73%). However, treated and untreated lakes experienced similar changes in submerged macrophyte richness and abundance. For example, total richness increased in 12 of 12 comparisons in both treated lakes (before: 1.1–2.3; after: 2.1–3.4 species/site) and untreated lakes (before: 1.2–1.6; after: 1.5–4.1 species/site). Total frequency increased in 4 of 12 comparisons in both treated lakes (before: 72–89%; after: 82–100%) and untreated lakes (before: 51–94%; after: 87–100%), with no significant change in the other comparisons. Results were similar for native species (see original paper for data). Methods: In May–June 1997, herbicide (fluoridone) was applied to four lakes. The aim was to maintain 5 µg/L of fluoridone in the upper 3 m of water, for 60 days. Submerged macrophytes were surveyed in a grid of points across the four treated lakes and four nearby untreated lakes, before intervention (May 1997) and for 15 months after (August 1997, May 1998 and August 1998).