Study finds potential link between herbicide treatment and hybrid watermilfoil

Research on Lake Minnetonka and Christmas Lake could guide future management decisions
Wednesday, February 1, 2017

A little known type of watermilfoil could be more invasive and tougher to control than the Eurasian variety that has irritated lake users for decades, according to new study findings from the Minnehaha Creek Watershed District (MCWD) and researchers from Montana State University and the University of Minnesota.

Using cutting-edge genetic screening techniques, the joint research project detected hybrid watermilfoil in several bays of Lake Minnetonka and nearby Christmas Lake and examined how it may be affected by large-scale herbicide applications to control Eurasian watermilfoil. Hybrid watermilfoil is a cross between the invasive Eurasian watermilfoil (commonly known as ?milfoil?) and northern watermilfoil, which is native to Minnesota. Genetic analysis is needed to properly identify hybrid watermilfoil.

Researchers discovered the hybrid plant was more prevalent in areas treated with herbicides than those with little management. This suggests large scale herbicide treatments could promote hybrid watermilfoil growth and some hybrids may show greater tolerance to treatment.

?As a pilot study, this research gets the ball rolling on understanding hybrid watermilfoil, its impacts, and how it can better be controlled,? said Eric Fieldseth, MCWD Aquatic Invasive Species Program Manager. ?These findings are an important first step toward developing more effective milfoil management strategies.?

The study also found that there are multiple, genetically-distinct types (genotypes) of invasive, hybrid and native watermilfoil. The results underscore the need for understanding the genetic makeup of the invasive plants in a lake before devising a plan to manage them, and following up with further genetic screening to guide future management.

?We were surprised to learn just how many genotypes of milfoil that are out there,? said Dr. Ray Newman, University of Minnesota Professor Fisheries. ?We need to get a handle on how this diversity and occurrence of hybrid is distributed in the metro as well as greater Minnesota lakes.?

?With this much diversity in the population, a successful milfoil management strategy may not be a ?one size fits all? approach.? said Dr. Ryan Thum, Montana State University Professor of Plant Sciences & Plant Pathology.  

The study, funded by a $35,000 grant from Hennepin County over the last 2 years, offers some of the first in-depth analysis on hybrid watermilfoil in Minnesota and provides a foundation for further research. Researchers are now working to expand the study across Minnesota and neighboring states.  

?We?re looking forward to seeing how these results compare with what's happening in other parts of the region,? said Thum. ?This research could have broad implications for managing milfoil in lakes throughout the Upper Midwest and beyond.?

Learn more and read the full study at www.minnehahacreek.org/milfoil