Minnesota DNR continues aggressive starry stonewort management

As the 2019 fishing and boating season gets underway, the Minnesota Department of Natural Resources is continuing and expanding a multi-faceted approach to combating the spread of starry stonewort, an aquatic invasive species.

The agency is issuing permits for pilot projects, working with local governments and lake associations, and partnering with researchers to limit starry stonewort in Minnesota after it was first confirmed in the state in 2015. This first confirmation was in Lake Koronis in Stearns County.

“Our main goals are to help prevent spread to other lakes, suppress starry stonewort in the 13 Minnesota lakes where it has been confirmed, reduce the recreational impacts and learn more about how we can control it,” said Heidi Wolf, DNR invasive species program supervisor.

Efforts include control of starry stonewort using hand removal, equipment, and copper herbicide treatments; evaluating the relative effectiveness of these methods; learning more about the biology of starry stonewort; working with lake associations and volunteer groups for early detection and monitoring; and educating boaters and anglers about how to prevent spreading starry stonewort and other invasive species. The DNR formed a starry stonewort guidance group in 2017 to review, permit and evaluate control projects.

Monitoring and research efforts have led to important new information:

Starry stonewort may double or triple in size within two to three years in a lake, once it becomes well established.
Hand removal by divers in small, localized areas appears to be effective, if done carefully. Repeated hand-pulling efforts or follow-up copper treatments may be necessary. Similar to other invasive plants in Minnesota, starry stonewort requires management on an annual basis if suppression is the goal.

Repeat copper treatments can reduce abundance and slow spread in a given season. Most native plant communities have seen minimal impacts from copper treatments, though a native type of algae that looks similar to starry stonewort, Chara, has been damaged by treatments.

The DNR’s partners in these efforts include the Minnesota Aquatic Invasive Species Research Center, the AIS Detectors group through University of Minnesota Extension, Minnesota Sea Grant, Wildlife Forever, lake associations and Minnesota counties with invasive species prevention programs.

Starry stonewort is an alga that looks similar to other native plants and can form dense mats, which can interfere with use of a lake and compete with native plants. It is most likely spread when fragments have not been properly cleaned from trailered boats, personal watercraft, docks, boat lifts, anchors or other water-related equipment.

The DNR reminds boaters and anglers to follow Minnesota laws to prevent the spread of aquatic invasive species:

Clean aquatic plants and animals from watercraft.
Drain all water by removing drain plugs and keep drain plugs out while transporting watercraft.
Dispose of unwanted bait in the trash.
Some invasive species are small and difficult to see at the access. To remove or kill them, take one or more of the following precautions before moving to another waterbody, especially after leaving infested waters:

Spray with high-pressure water.
Rinse with very hot water (120 degrees for at least two minutes or 140 degrees for at least 10 seconds).
Dry for at least five days.

Details about starry stonewort and other aquatic invasive species are available at mndnr.gov/ais.