Eurasian and hybrid watermilfoil genotype distribution in Minnesota

Invasive Eurasian and native northern watermilfoil can hybridize. Researchers identified hybrid watermilfoil in 39 lakes across the state. Hybrid watermilfoil is genetically more diverse than Eurasian watermilfoil and has potential to be more invasive and resistant to herbicides; several potentially problematic genotypes have been identified for further study.

Phase II progress:

Invasive Eurasian and native northern watermilfoil can hybridize and some genotypes of hybrid watermilfoil have been shown to be more invasive or resistant to herbicidal control. Our aim was to determine the occurrence and distribution of hybrid watermilfoil in Minnesota, assess the response of different genotypes to herbicidal management, identify potentially problematic genotypes and assess the response of some of these genotypes to herbicide in controlled laboratory conditions. We assessed watermilfoil genetic composition in 81 waterbodies in Minnesota; 55 lakes had pure Eurasian, mostly one widespread genotype that was found in 52 lakes. Eight other Eurasian genotypes were found. We identified hybrid watermilfoil in 39 lakes across the state, mostly, but not entirely, in the Twin Cities Metro. Hybrid watermilfoil is genetically more diverse than Eurasian watermilfoil and 82 genotypes were found. Most lakes have one unique genotype of hybrid but multiple genotypes were found in several lakes and 26 have been identified in Lake Minnetonka. One hybrid genotype has been found in 10 lakes. No clearly problematic genotypes have been identified in Minnesota but we did find changes in genotype frequency with management in an assessment of 5 managed waterbodies and 3 reference waterbodies over 3 years. Several hybrid genotypes have expanded while Eurasian decreased and two hybrids from Lake Minnetonka have persistently rebounded after control. We also identified one genotype of northern watermilfoil that may be less affected by herbicide treatment.  We conducted laboratory performance and herbicide challenge tests with the widespread Eurasian genotype and 4 hybrid genotypes. Additional experiments are needed but preliminary results suggest that two hybrid genotypes may be more tolerant of 2,4-D than the widespread Eurasian and two other hybrid genotypes. Continued identification of hybrid genotypes and response to management will improve milfoil management by allowing manager to appropriate controls for their particular populations. 

Phase II: Genetics to improve hybrid and Eurasian watermilfoil management

The first phase of this project identified what taxa of milfoil are present where in Minnesota. In order to better manage invasive milfoil we need to know the distribution of hybrid genotypes, understand factors that promote occurrence and development of hybrids, and identify specific hybrids that may need special management attention (e.g., herbicide tolerance). This phase of the study will use the understanding of genetic distribution within and among lakes and differences in response to management gained from the first phase to further identify problematic genotypes and develop a catalog of genotypes to improve management. Specifically, this project will:

  • Assess the response of hybrid watermilfoil to herbicidal control in a set of intensively managed lakes.
  • Assess the distribution of hybrid watermilfoil genotypes from under-sampled regions and problematic lakes.
  • Pilot herbicide challenge-screening of several hybrid genotypes identified in objectives 1 and 2 as potentially problematic.
  • Assess the need for a genetic testing service, and its potential structure.

By building a “catalog” of genotypes (distinguished by molecular markers) present, and for a subset identifying their herbicide response properties, we will begin to identify problematic genotypes requiring targeted management in Minnesota. Over the long term, this project is part of a research program aimed at identifying the genetic basis of plant traits that are important to management outcomes. The ultimate goal is to have genetic/genomic predictors of important plant traits that can be used in developing and supporting management plans.

Phase I

Invasive Eurasian watermilfoil is known to hybridize with native Northern watermilfoil in some lakes in Minnesota. This hybrid watermilfoil is also invasive and some strains have shown resistance to management efforts including herbicide treatments. However, much is unknown about the genetic makeup, diversity, and distribution of hybrid watermilfoil throughout the state, making management efforts very difficult. 

In partnership with Montana State University, this project will quantify the genetic diversity of Eurasian, hybrid, and northern watermilfoil in sixty Minnesota lakes and will help answer questions such as:

  • Do different genotypes present increased invasiveness or tolerance to control techniques?
  • Are there patterns of hybrid watermilfoil invasion? Are plants hybridizing within a lake, or is one hybrid strain being moved among lakes?
  • How is hybrid watermilfoil interacting with native plant communities?

The collected watermilfoil samples will first be genetically identified as Eurasian, northern, or hybrid. Later, the hybrid samples will be genotyped using molecular genetic techniques to determine whether specific genotypes are widespread or have restricted distribution, related to management activities or environmental factors, or if they’re hybridizing within lakes.

Understanding the patterns of invasion as well as genetic diversity of this plant to help lake managers develop and refine management strategies.

Phase I Outcomes:

Researchers assessed genetic variation (diversity) and distribution of specific genotypes and began an assessment of the response of watermilfoil and genotypes to management with herbicides. They sampled 64 lakes across the state stratified by county, size, and duration of infestation and collected milfoil from random points. The DNA from the milfoil samples was analyzed to determine taxon (Eurasian, northern or hybrid) and specific genotypes.

Eurasian was found in 43 lakes, hybrid in 28 lakes, and northern in 23 lakes. Hybrid was much more common in the Twin Cities metro area, whereas Eurasian was broadly distributed. Northern watermilfoil was the most diverse with 84 genotypes, none shared across lakes. In contrast, they found one widespread genotype of Eurasian and six others found in individual lakes. Hybrid was intermediate in diversity with 53 genotypes; most lakes had only 1 unique genotype but 40% had multiple hybrid genotypes.  Several genotypes were found in multiple lakes indicating clonal spread. The high diversity of hybrid watermilfoil indicates there is much potential for selection of problematic genotypes that are resistant to herbicides or that are competitively superior. There are numerous hybrid genotypes that could become problematic, but few have been widely distributed. Researchers have not yet identified any clearly problematic genotypes in Minnesota but lakes with unexplained treatment failures, and populations with high diversity, this should be assessed. A strategy to identify and test problematic genotypes will be addressed in Phase II of this project (above).

Project manager: Ray Newman

Funded by: Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources

Project start date: 2017

Project end date: 2019


Final report