Phenology and management of triploid flowering rush (Butomus umbellatus L.)

• Main Author: Turnage, Lee Gray, Jr.
• Format: Text
• Language: English
• Published: Scholars Junction 2021
• Subjects: Aquatic invasive species; herbicide; adaptive management; Canada; Butomus umbellatus
• Online Access: https://scholarsjunction.msstate.edu/td/5158; https://scholarsjunction.msstate.edu/cgi/viewcontent.cgi?article=6158&context=td

Flowering rush (Butomus umbellatus L.) is a perennial wetland/aquatic plant that is native to Eurasia but has invaded North America and spread across Southern Canada and the Northern U.S. where it thrives along wetlands, shallow shorelines, and in submersed habitats of lakes, ponds, streams, rivers, and reservoirs. Little is known about the life cycle of flowering rush in its invaded range as only one study has investigated flowering rush phenology in Minnesota, USA. As flowering rush continues to expand its range southward in the U.S. it is imperative that resource managers 1) better understand the plants life cycle, 2) identify more aggressive and 3) selective herbicide strategies, and 4) utilize adaptive management protocols. In a mesocosm experiment, flowering rush grown in southern climates produced less overall biomass but produced more buds than recorded in northern populations. A second mesocosm study using one to four biweekly sequential diquat (0.37 mg L-1) treatments reduced flowering rush biomass and rhizome bud density by 62 to 100% one year after treatment. Additionally, there were no differences among diquat treatments suggesting that more aggressive diquat protocols may not be useful. In field trials, flowering rush was selectively reduced 92 to 99% by diquat treatments over two years, while hardstem bulrush was not affected. In mesocosms, flowering rush and hardstem bulrush were exposed to the contact herbicides diquat, endothall, copper, carfentrazone-ethyl, and flumioxazin; endothall (3.0 mg L-1) selectively reduced aboveground biomass of flowering rush by 69% and diquat (0.19 mg L-1) selectively reduced belowground biomass by 77%. None of the other herbicides affected flowering rush. In a Minnesota field project to identify adaptive control strategies, treatment sites were designated as having very-low, low, or high flowering rush prevalence with each receiving no, one, or two diquat treatments (0.37 mg L-1), respectively. Flowering rush did not increase after single diquat applications in low prevalence sites while prevalence declined in high prevalence sites. This suggests that single diquat applications are suitable to maintain control of sites with low flowering rush prevalence allowing resource managers to allocate unused resources elsewhere.