What the Science Says: Management Options
An objective look at every recognized EWM management method — what each one does, what the science shows, and how they fit together.
Managing Eurasian watermilfoil is not a one-size-fits-all undertaking. Different lake environments, different infestation levels, and different community circumstances call for different tools. The MFA has researched and applied virtually every recognized management method available to Wisconsin lake associations.
Herbicide Treatment
Targeted herbicide application is considered one of the most effective tools for controlling established EWM populations, particularly in deeper water where mechanical methods are limited. The MFA's 2026 permit application proposes use of ProcellaCOR EC (active ingredient: florpyrauxifen-benzyl), a next-generation selective herbicide that represents a meaningful advance over the 2,4-D treatments used in prior years.
ProcellaCOR works by mimicking the plant growth hormone auxin, causing uncontrolled cell growth that is lethal to EWM while leaving most native aquatic plants unaffected. It requires 40 to 100 times less active ingredient than older herbicides — a substantially lower chemical load. It degrades quickly in the water column with a half-life of one to six days in sunlit conditions, so it does not persist or accumulate in the lake. It was specifically registered by the EPA for use in rice-growing operations, meaning it was evaluated and approved in precisely the context most relevant to the Minong Flowage: a water body with wild rice.
Laboratory and field studies have shown little to no activity against common native submersed and floating-leaf species. In a peer-reviewed field study of a comparable Great Lakes region lake, of nine native plant species present in treatment areas, six actually increased in frequency after treatment — with native species richness rising at every surveyed transect. Dense EWM beds, once cleared, are rapidly recolonized by native plants. (Davidson, 2023 — Management of Biological Invasions)
The ecological benefit extends beyond the directly treated areas. The Flowage's heaviest, longest-established EWM beds are the primary source of fragmentation and reseeding throughout the littoral zone. Eliminating them reduces recolonization pressure well beyond the treatment boundaries and opens habitat for native vegetation to recover across the lake. Paired with monitoring and adaptive management, this approach is designed to produce measurable, durable results.
Mechanical Harvesting
Mechanical harvesters cut and collect EWM from the water column, providing immediate improvement in navigability and recreation access. Most effective in shallow water and high-use areas. Dark water conditions and submerged stumps on the Flowage make harvesting a complement to other methods rather than a standalone solution.
Water Level Drawdown
A winter drawdown — distinct from a summer drawdown, which does not effectively target EWM — exposes root systems to freezing temperatures. The 2013–14 drawdown produced the lowest EWM coverage ever recorded on the Flowage as a secondary effect. A targeted winter drawdown in 2021–22 yielded limited results, with EWM rapidly repopulating. Any future drawdown requires broad community consensus and approvals from multiple governmental authorities.
Hand and Physical Removal
Volunteer removal contributes meaningfully in accessible shallow areas and is an important part of community engagement and shoreline stewardship. At 257 acres across 37 beds, physical removal alone cannot address the Flowage's infestation — but every effort counts.
Biological Controls
EWM-specific weevil (Euhrychiopsis lecontei) programs ran on the Flowage from 2009 through 2016. Results were consistent with broader scientific findings: weevil programs work best in smaller, isolated water bodies and have not achieved population-level reduction on the Flowage. The MFA continues to monitor developments in biological control research.
Integrated Management
The MFA's 2024–2028 Aquatic Plant Management Plan reflects two decades of hard-won experience: no single approach is sufficient. An integrated strategy — combining the right tools, targeted at the right areas, in the right seasons, with ongoing monitoring and adaptive management — is the only path to sustainable EWM control in a water body as large and complex as the Minong Flowage.
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