Scientific Name: Butomus umbellatus
Common Names: flowering rush, grassy rush, water gladiolus
History: Flowering rush is an aquatic perennial that originated from Eurasia and was brought to the U.S. as an ornamental. The earliest documented finding in North America was found in the St. Lawrence River in 1897 and by 1964 it had reached the Northern shore of Flathead Lake in Montana.
Roots: The roots of flowering rush are fleshy and rhizomatous, which means they have rhizomes or underground, horizontal, stems that produce more roots and shoots. Minor disturbances in the water can cause the rhizomes to break free and start to produce new plants. The roots are the main method of reproduction.
Stems and Leaves: Flowering rush has triangular, straight stems that emerge out of the water anywhere from one to five feet. The leaves are triangular, sword like, grow into a spiral at the the tip, and are spongy when squished. When the depth of the water exceeds three meters (10 feet) the plant grows submerged and the leaves become limp and ribbon like.
Flowers and Seeds: The flowers are light pink in color and two to two and half cm wide. They have six petals, three of which are actually the sepals and are slightly green and there are nine stamens. Three grow in cluster with the remaining six growing around them. Twenty to 50 flowers grow in an umbrella-like cluster at the top of each stem and each flower produces up to 200 seeds. Flowering rush blooms from early summer to mid fall.
Reproduction and Other Facts: Flowering rush has two types, one flowers regularly and produces viable seeds. The other type does not flower regularly and it is sterile, or doesn't produce seeds. The populations that infest Montana are, fortunately, the non-fertile type that doesn't flower often. This doesn't stop the spread of this weed though because the main method of reproduction is through the rhizomes. The rhizomes cause flowering rush to start its growing season as soon as the middle of February which is much earlier than other plants.
Environments Favorable to Infestation: Slow moving bodies of water like lakes, irrigation ditches, and marshes are good areas for flowering rush to establish. Usually shallow areas are best but there have been observations of flowering rush growing in water up to six meters (20 feet) deep. Flowering rush can not grow in shade or areas where native or previously existing vegetation is thick.
Environmental and Economic Impacts: Flowering rush clogs irrigation ditches and takes over shallow areas in lakes and rivers such as boat launches or moorings and impedes recreational activities. It creates problems for swimmers and boats and even native species of fish. In Flathead Lake, cutthroat trout and bull trout are adapted to open waters and the flowering rush is posing problems for them and creating habitat for predators to hide in. The flowering rush also creates habitat for the great pond snail which is a host for several parasites and causes swimmers itch.
Range: Flowering rush, as of 2015, infests 16 of the lower 48 states. In Montana it infests four counties: Flathead, Lake, Missoula, and Sanders.
Prevention: Do not purchase this plant, it is still sold as a garden plant in the U.S.. Wash all recreational equipment and clean all weeds off boat propellers.
Mechanical: Hand digging for very small infestations may be used but it usually has to be repeated and must be very carefully done. Bottom Barriers can be used in small areas below boat moorings. Cutting is another form of control but it its not recommended because it causes rhizomes to break loose and it has to be repeated continuously.
Cultural: Establishing native plants has shown to be effective in slowing the spread of flowering rush.
Biological: There is not currently a bio-control agent for flowering rush.
Chemical: There are currently no herbicides approved for use in the U.S. but there is ongoing research over the use of Habitat and Clearcast.
1."Biology, Ecology, and Management of Flowering Rush." Web. 10 Aug. 2015. <http://store.msuextension.org/publications/AgandNaturalResources/EB0201.pdf>.
2."Weed of the Week." Web. 10 Aug. 2015. <http://na.fs.fed.us/fhp/invasive_plants/weeds/flowering-rush.pdf>.