Clear Lake - The Iowa Department of Natural Resources (DNR) treated Clear Lake last week with the approved aquatic herbicide, Sonar A.S. to eliminate Eurasian watermilfoil.
Sonar A.S. has successfully eradicated Eurasian watermilfoil from other lakes in Iowa by preventing the plant from producing a pigment needed for photosynthesis, starving the plant over several weeks. The herbicide has no restrictions for swimming, fishing, irrigation, or drinking water at the planned dose.
Treatments will continue through next spring. DNR biologists will test the water throughout Clear Lake every two weeks to measure concentration of the herbicide and prescribe “bumps” of herbicide to maintain the herbicide concentration. These bumps can even be done through the ice.
The herbicide is effective at very low concentrations, explains Jason Euchner, Aquatic Plant Management Biologist for the DNR. “We will treat the lake at 5 parts per billion. Only one hundred and thirty three gallons of the herbicide will be needed to reach the desired concentration.”
A group of representatives from Clear Lake have been working with the Iowa DNR to formulate a management plan that could eliminate the plant from the lake. Fast action is required since the plant is quickly expanding and could infest other lakes and wetlands in the area making eradication nearly impossible.
Eurasian watermilfoil and curly-leaf pondweed, another invasive species in Clear Lake, are very susceptible to Sonar A.S. The treatment should only impact these two species. Since Eurasian watermilfoil reproduces mainly by fragmentation, a single treatment can eliminate the plant. Curlyleaf pondweed will be drastically reduced because of the treatment, but will likely rebound since it produces seed-like structures that help it repopulate.
The DNR and local partners are starting to build a long-term management plan for the area. If the project is successful, prevention will continue to be the best way to guard against future re-introduction. If the treatment is not successful, the group will discuss long-term management strategies.
“Keeping the plant out of the lake over the past 30 years has allowed time for better tools to be developed to manage this plant,” said Scott Grummer, District Fisheries Biologist with the DNR. “I’m confident we can work together locally to manage it long-term. In the meantime, we plan to take our best shot at eliminating it.”