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Ecology and Management of Flowering Rush in the Detroit Lakes Chain.

Madsen, J. D., Cheshier, J., Marko, M., & Guetter, T. (2010). Ecology and Management of Flowering Rush in the Detroit Lakes Chain. 2010 Minnesota-Wisconsin Invasive Species Conference, November 8-10, 2010. St. Paul, MN.


Flowering rush (Butomus umbellatus L.) is a lesser-known invasive aquatic plant, with infestations appearing in Flathead Lake, MT downstream into Idaho and Washington, and in the Detroit Lakes chain in Minnesota. While several genetic and taxonomic studies have been completed, little has been done on the ecology and management. We have initiated a two-year field study in May 2010 for the Detroit Lake chain, examining the phenology, depth distribution, and biomass allocation with depth in the five lakes of the Detroit Lakes chain. For the phenology study, we are sampling four sites every three weeks from May to October and every other month from November to April. Twenty samples of flowering rush per site will be taken using a 15-cm diameter biomass core sampler. In addition, twenty point samples will be recorded for phenological characteristics of hardstem bulrush (Schoenoplectus acutus (Muhl. ex Bigelow) A.& D. Löve). Ecological distribution will be evaluated using a point intercept survey in all five lakes in the chain, visiting points in a 100m grid interval throughout the system. At each point, plant species presence will be recorded and depth measured. At every other point, a sediment sample will be taken using a 5-cm diameter core for particle size analysis. Previous experience in managing flowering rush has shown that Imazapyr was effective at controlling emergent flowering rush, but did not control submersed plants. We initiated a field trial of endothall on flowering rush in May 2010. Twelve 0.5 ha plots were selected for treatment, with four untreated reference plots. Our trials included treatments of endothall once (May), twice (May and June), or three times (May, June, and July) with an initial target concentration of 3.0 mg ai/L in the water, or 0.44 kg ai/ha-m. Each treatment was replicated in four plots. Preliminary results of these three studies will be presented.

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