Permits issued with a variance

To treat more than 15% of the littoral area with herbicide or harvest more than 50%, consultation between the DNR and the project proposer is necessary.

Before meeting with the DNR, please assemble the necessary information in a Lake Vegetation and Water Quality Assessment. Contact an Invasive Species Specialist for your area to discuss the current conditions and possible approaches to management.

If a proposal is approved, the DNR and project proposer will write a Lake Vegetation Management Plan.

Eurasian watermilfoil

In review of such proposals, the principle determining factors that the DNR will consider are:

  1. water clarity and
  2. distribution and composition of the plant community.
Water clarity is a major determining factor:

  • In lakes where clarity as indicated by Secchi depth is greater than 2m:
    • Proposal will be considered further
    • Consideration will also be given to the distribution and composition of the plant community.
    • Justification-lake-wide reduction in Eurasian watermilfoil has been shown to be followed by an increase in native plants.
  • In lakes where clarity as indicated by Secchi depth is 2m or less:
    • Consideration will also be given to the distribution and composition of the plant community.
    • Proposer likely will be directed to develop an approach to management that involves application of herbicide to no more than 15% of the littoral area.
    • Justification - there is significant risk that lake-wide reduction in Eurasian watermilfoil may not be followed by an increase in native plants and water quality maybe reduced.

Curly-leaf pondweed

Research and monitoring over the past ten years has shown that the most successful (meeting project goals and costs) projects done to control curly-leaf pondweed are those that involve application of herbicide to less than 15% of the littoral area.

  • Proposed applications of herbicide to more than 15% of the littoral area may be supported if the proposals include:
    • evaluation including monitoring by applicant or third party (other than the commercial herbicide applicator for the project) of
    • unique control treatments (e.g. alum, carp removal, or drawdowns)
  • Justification - There has been a focus over the last ten years on research and monitoring of herbicide treatment to control curly-leaf pondweed. These projects indicate that this method has been less effective especially on low clarity lakes. Specifically, treatments did not lead to an increase in water clarity. Although lake-wide reductions in curly-leaf were obtained, matching increases in native plants were not observed. Lake-wide control of curly-leaf pondweed in most cases appears to move in the direction of reducing the amount of vegetation in low clarity or eutrophic lakes.
    • Nevertheless, there is little information available on control of curly-leaf pondweed in combination with other management actions, such as drawdown, application of alum, removal of common carp, etc. Applicants who propose to explore these techniques further and who are able to monitor outcomes will provide needed information to lake managers.

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