Join CLRMA member Elizabeth Brown and U.S. Department of Agriculture’s Dr. John Madsen for a virtual lunchtime webinar titled…Flowering Rush Identification, Biology, and Management.

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Flowering rush (Butomus umbellatus L.) is becoming a widespread invasive weed in the waters of the West and Midwest. Flowering rush causes a number of nuisance problems including obstruction shorelines, reducing irrigation flow, and providing habitat for nonnative warmwater fish. This species is distinctive in appearance, though is often confused with other emergent and submersed species. Flowering rush occurs as both diploid and triploid biotypes, but western US populations are largely the triploid biotype. Recently published research has identified six genotypes in the US, but one genotype in particular dominates in the western US. While an international group is actively looking for biological control agents, at this time no insect biocontrol agents are available. Several herbicides are available and effective for chemical control of flowering rush, with three application modes studied: foliar application to emergent leaves, submersed inject to submersed leaves, and bare-ground applications to newly-sprouted plants in the spring. Preemergent applications have also been studied. While harvesting has been used to manage foliage, it is not a long-term management technique. Various physical techniques, such as digging and bottom barriers, have also been used. Whichever technique is used, it is essential that the manager target the rhizome bud stage to reduce propagule production.

John D. Madsen, PhD. is Research Biologist with the US Department of Agriculture, Agricultural Research Service, Invasive Species and Pollinator Health Research Unit in Davis, California, USA. His work focuses on the biology, ecology and management of aquatic plants, particularly nuisance-forming species.