Effects of Repeated Fluridone Treatments Over Nine Years to Control Eurasian Watermilfoil in a Mesotrophic Lake

摘要

Eurasian watermilfoil (Myriophyllum spicatum L.), hereafter called milfoil, is a non-native, invasive submersed aquatic plant that was first found in Minnesota in 1987. Milfoil can limit recreational activities on water bodies and alter aquatic ecosystems by displacing native plants (Madsen et al. 1991). In 1988 milfoil was discovered in Lac Lavon (44°43'11"N, 93°14'43"W), a 22 ha (55 acre) former gravel pit just south of the Twin Cities metropolitan area in Minnesota. Lac Lavon is considered mesotrophic by the Minnesota Pollution Control Agency (2005) based on water clarity (4.1 m), chlorophyll-a (4 ppb), and total phosphorus (14 ppb). By 1996 milfoil had become the dominant plant in the lake, which created problems for users of Lac Lavon. In 1996, the cities of Apple Valley and Burnsville, in cooperation with the Lac Lavon Association, contracted to have the lake treated with Sonar A.S. herbicide, in which the active ingredient is fluridone (l-methyl-3-phenyl-5- [3-(trifluoromethyl) phenyl] -4(1 H)-pyri-dinone). The Minnesota Department of Natural Resources (DNR) evaluated the effects of this treatment by monitoring the plant community one to two times per year over a period of nine years, during which the lake was subjected to three whole-lake treatments with fluridone.