Environmental response of a Lake Superior coastal waterway to Eurasian watermilfoil management

Background/Question/Methods

Eurasian watermilfoil (Myriophyllum spicatum, EWM) is a prolific invasive plant in North America. Populations of EWM have recently been established in coastal waterways of the Upper Great Lakes, where cold water temperatures and intense circulation patterns present a unique management challenge. Management of EWM is further complicated by its ability to hybridize with native northern watermilfoil (M. sibiricum), producing a community of watermilfoil with varying resistance and susceptibility to management activities. The goal of our study is to conduct a multi-faceted control program to identify the best management practices for arresting the growth and spread of EWM and its hybrids in the Upper Great Lakes via a multi-year treatment and monitoring program in the Keweenaw Waterway, Michigan while also documenting the ecological effects management has on these water bodies. In the summer of 2014, we treated waterways with the herbicide 2,4-D then returned post treatment and assessed the plant community, water quality, and water chemistry. 

Results/Conclusions

Areas treated with 2,4-D  show a significant decrease in EWM biomass six weeks after herbicide treatment, but an unexpected increase in dominance by watermilfoil hybrids. There were no changes in total biomass of non-target macrophytes, phytoplankton, or water chemistry after treatment. Our future plans will explore the efficacy and logistics of supplementing herbicide-based approaches with non-chemical control measures to improve management of EWM and its hybrids, with the ultimate goal of creating more cost- and time- effective treatment options.