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Idaho Enterprise

War on Weeds—Weeds are Everybody’s Problem

Feb 22, 2024 02:27PM ● By Justin Hatch

THE ISSUE:  Flowering Rush  

 Flowering rush (Butomus Umbellatus) is a rhizomatous aquatic perennial weed that is native to Eurasia. It invades lakeshores, wetlands, canals, and slow-moving bodies of water. It was first found in Idaho in the Snake River near Idaho Falls in 1949. Flowering rush roots underwater and can survive completely submerged but leaves usually emerge from the water. This plant negatively impacts native ecosystems, irrigation systems, and recreational opportunities. 

Flowering rush has dark green leaves which can grow up to 3 ft out of the water. Leaves have a triangle shaped cross section but should not be confused with sedges which also have triangle shaped cross section. Leaves are sword shaped and often twist near the top. Flowers are pink in color and are formed in clusters. Some flowering rush populations in the eastern U.S. can produce seeds, other population found in the west are sterile. While in our region it can’t reproduce via seed, it can reproduce. Flowering rush roots are rhizomatous, which basically means they form underground stems. These rhizomes break easily and can be transported in currents. When they come to rest, they can root in a new location, and ultimately start a new colony.  

Integrated Pest Management (IPM) Options: 

Prevention— Learn to identify this plant. Never transport unknown plant material. Clean boats and recreational equipment by removing plant material before transporting. 

Mechanical— Hand digging can be one of the most effective ways to remove small infestations if rhizomes are completely removed. Otherwise, rhizomes will be disbursed making the problem worse. Mechanical aquatic vegetation rakes can be effectively used on large infestations.   

Cultural— Encouraging native plant growth such as reeds will provide competition and make it difficult for flowering rush to establish.  

Chemical—Imazapyr, Imazamox, and Glyphosate are herbicide active ingredients that can help to control flowering rush. Care must be taken when applying herbicides in irrigation water; herbicides can be carried into fields of sensitive crops.  Always read and follow herbicide label directions.

Justin Hatch, University of Idaho Extension Agriculture Educator in Caribou County. 208-547-3205
[email protected]

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