Work is underway to learn more about how to control the spread of flowering rush, a nonnative plant that is already in Flathead Lake. Flowering rush causes concern for boaters, endangers wildlife habitat, and may have unknown ecological impacts on Flathead Lake.

Untrue to its name, flowering rush rarely flowers in Flathead Lake. The plant has been steadily increasing in shallow bays and marinas in South Bay (see photos, right), Finley Point, Yellow Bay, the West shore, King’s Point, Dayton, and Pleasant Bay areas. Flowering rush incursions start as individual slender grass-like plants that become expansive monocultures. The plant grows from the shoreline to 13-foot deep water. Leaves are highly characteristic, with a triangular cross section, upright with twisted ends in shallow water, and leaves lax in deeper water. The plant forms extensive rhizomes about four to six inches deep.

Web sites typically display photos of flowering versions, but the vegetative appearance is similar. See:

• http://plants.ifas.ufl.edu/butumb.html for photos showing typical infestations, and
• http://plants.ifas.ufl.edu/butumbdr.jpg to see a line drawing of rush.

Pulling propagates

Flowering rush spreads primarily when disturbed, spreading rhizomes and releasing vegetative bulblets that form new plants. Boats can disturb flowering rush and transport rhizomes and bulblets, and lake currents can distribute rush that is disturbed by construction, digging, cutting, and pulling.

Researchers studying situation

Salish Kootenai College, University of Montana Department of Biological Sciences, Montana State University Center for Invasive Plants, and the University of Montana Flathead Lake Biological Station are working to more clearly understand the distribution and ecological impacts of flowering rush (Butomus umbellatus).

Researchers are gathering data to build a spatial model and inventory of flowering rush in Flathead Lake to identify the infestation and dispersal vectors, predict the biological potential and eventual unchecked extent of the infestation, and test management alternatives to be implemented in winter and spring of 2008. The Biological Station is investigating impacts to lake ecology. We plan to survey lake users to identify locations of flowering rush, and meet with cooperators to plan management strategies and participate in testing measures to slow the spread of this invasive species.

More information

Please contact Confederated Salish & Kootenai Tribes Extension Agent Virgil Dupuis at 406-275-4899 or virgil_dupuis@skc.edu for more information. Virgil Dupuis.