Integrated management of nonnative and hybrid Eurasian Watermilfoil in the Portage Waterway of the Upper Peninsula of Michigan

Eurasian watermilfoil is a widespread aquatic invasive macrophyte, which recently has emerged as a management concern in sheltered and connected waterways in the Upper Great Lakes region. For example, in summer 2012 spreading populations of Eurasian watermilfoil and hybrids (Eurasian x Northern watermilfoil) were identified in the Portage Waterway of Lake Superior, which bisects the Keweenaw Peninsula of Michigan’s Upper Peninsula. Over the last two years of this study, we have partnered with local townships actively surveying and managing these populations to quantify the efficacy of herbicide treatments, while also assessing possible effects on non-target species. In both years we found that herbicide treatments reduced the abundance and biomass of Eurasian watermilfoil immediately following treatment, but over the two years of treatment hybrid water milfoil persisted and established high abundances, perhaps due to reduced sensitivity to herbicides by these hybrids. We found no decreases in the total biomass of off-target species; however, when analyzed separately from dicots, the monocot showed a significant increase in biomass. We are now studying alternate management approaches such as native species replanting that could be used in combination with herbicides to improve the long-term efficacy of treatment efforts. To monitor the effectiveness of these treatments and to improve early detection, we are testing novel tools to map the presence and extent of invasive watermilfoil in shallow waters, including imagery obtained using unmanned aerial vehicles and side-scan sonar. Finally, we will describe integrated pest management and how it could be used as a framework for planning and resource allocation for the management of invasive watermilfoils and other aquatic invasive species