Building a Centralized Database of Watermilfoil Strain Geographic Distribution and Herbicide Response for Use in Management Decision-Making

Research in Michigan has identified watermilfoil strains or genotypes that are more invasive or are resistant to specific herbicides and recent work has begun to characterize the response of different Michigan strains to specific herbicides. Much less is known about the response of strains in Wisconsin or Minnesota but recent surveys, and assessment of responses to field management have identified a number of strains from Minnesota that should be evaluated for response to herbicides. The aim of this project is to add to our existing database of strain herbicide responses by characterizing several Minnesota strains.

Based on previous MAISRC research and extensive genetic surveys in Minnesota, researchers have identified several strains for herbicide characterization. These include:
1) A widespread hybrid strain that has been found in at least ten lakes to date.
2) A widespread Eurasian watermilfoil strain that is found in many lakes throughout the state.
3) Two hybrid genotypes that are common and increasing in treated Bays of Lake Minnetonka.
4) A hybrid genotype from Ham Lake that has had questionable herbicide response.
5) Up to three additional strains identified in consultation with lake management professionals, based on their qualitative observations of response to operational management.
In the first year, researchers will focus on characterizing the 2,4-D response for the above genotypes. The team will focus first on 2,4-D because it has been the most commonly-used herbicide for watermilfoil control in Minnesota for the past several decades, and the above strains are all likely to have a long history of 2,4-D exposure (within and among water bodies). Depending on the results of year 1 experiments and reports from field treatments, researchers will then characterize the response of these genotypes to other herbicides that are increasingly used in Minnesota (e.g., florpyrauxifen-benzyl or fluridone), or they will assess the response of additional strains to 2,4-D. If resistant strains are found in year 1 then they will focus efforts on additional herbicides to determine if they may be suitable options. If no 2,4-D resistant strains are identified in year 1, they will test additional strains for response to 2,4-D. The team will also catalog, display, andshare genotype information collected as part of the overall project. 

Project manager: Ray Newman

Funded by: USFWS and Montana State University

Project start date: October 2021

Project end date: September 2023