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Management of Aquatic Invasive Plants

Purple loosestrife plant

Management of invasive aquatic plants that involves the application of herbicides to public waters in Minnesota requires a permit from the DNR.

The cumulative amount of area in a lake where aquatic plants may be controlled with herbicides may not exceed 15% of the littoral area. The littoral area is the part of the lake where rooted aquatic plants will grow and is limited to a depth of 15 feet or less.

Treatment of more than 15% of the littoral zone may be allowed under a variance. Before this treatment is allowed, consultation between the DNR and the proposer is necessary.

Invasive Aquatic Plant Management Permits

Permit Application

To apply for a permit to manage invasive aquatic plants, complete the permit application PDF and submit it to your local aquatic invasive species specialist. Additional instructions PDF are available.

Permit Criteria

The following criteria will be used to evaluate applications for invasive aquatic plant management permits. A successful application will receive a "yes" to questions #1 - #7.

  1. Has the application for an invasive aquatic plant management permit been completed and submitted properly?
    1. Has a waiver from the requirement to provide signatures been requested?
  2. Is the target invasive aquatic plant(s) found in the proposed treatment area?
  3. Is the proposed treatment technique selective for the target invasive plant(s)?
  4. Is the purpose of the proposed treatment to significantly reduce the lakewide or baywide abundance of the target invasive plant(s)?
    • Treatments that work at a scale to cause a significant reduction of the lakewide or baywide abundance can range from a small set of scattered patches to a few large concentrations of the target invasive plant. Treatments can reduce interference with recreation by focusing on large concentrations of target invasives that mat on the surface or smaller patches that impede surface water use in strategic locations. Also, treatments can reduce the risk of spread by focusing on public access sites or heavily used travel routes.
  5. Does the proposed treatment minimize potential negative impacts to aquatic habitat, including water quality?
  6. If the proposed treatment includes near shore areas (within 150 feet of shore), are these near shore areas included in the application for an invasive aquatic plant management permit for reasons described in #4 above and not just to provide a landowner access to the lake?
  7. If the proposed treatment of invasive aquatic plants, when combined with all other treatment on the lake, does not exceed the limits on the littoral area allowed for treatment, then stop here. If the proposed treatment results in control that exceeds the limits, see the 'Special Permits' information below.
    • The limit on littoral area allowed for treatment with herbicide is 15% and the limit for mechanical treatment is 50%. The limit on the littoral area allowed for both herbicide and mechanical treatment combined is 50%. These limits are cumulative and include all permitted aquatic plant management activities on the lake.

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 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 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.

Grant Programs

Grant money may be available to support aquatic invasive plant management.

Aquatic Plant Management References

The document below contains links to a few selected references on management of aquatic plants, with an emphasis on invasive aquatic plants.

Past Stakeholder Engagement

The DNR has engaged with stakeholders to improve management of invasive aquatic plants. Phase I focused on suggested actions and Phase II developed recommendations for possible revisions to Minnesota's approach to management of invasive aquatic plants.

Phase I

Phase II

Contact

Chip Welling, Aquatic Invasive Species Management Coordinator
chip.welling@state.mn.us
500 Lafayette Rd, Box 25
St Paul, MN 55155-4025
651-259-5149