Selective control of flowering rush in mesocosms and field sites

Authors: TURNAGE, GRAY - Mississippi State University; Madsen, John; WERSAL, RYAN - Minnesota State University; BYRD, JOHN - Mississippi State University; ALCOTT, BRENT - Pelican River Watershed District; GUETTER, TERA - Pelican River Watershed District

Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2019
Publication Date: 7/1/2020
Citation: Turnage, G., Madsen, J.D., Wersal, R.M., Byrd, J.D., Alcott, B., Guetter, T. 2020. Selective control of flowering rush in mesocosms and field sites. Journal of Aquatic Plant Management. 58:92-97.

Interpretive Summary: This study demonstrates in both controlled mesocosm conditions and in field plots that flowering rush may be controlled with diquat or endothall with minimal impact on the desirable native plant hardstem bulrush. While the other contact herbicides tested (copper complexes, carfentrazone-ethyl, and flumioxazin) did not adversely affect hardstem bulrush, they also did not control flowering rush relative to the untreated reference.

Technical Abstract: Flowering rush is an invasive aquatic plant species that is spreading across the northern U.S. and southern Canada. Flowering rush can displace many native aquatic plants species like hardstem bulrush, an emergent aquatic plant that is used as spawning habitat by many native fish species. Previous studies show that repeated applications of contact herbicides can control flowering rush; however, it is unknown if these herbicides can be used to selectively control flowering rush co-occuring with hardstem bulrush. The purpose of this study was to determine if selective control of flowering rush was possible with repeat contact herbicide applications in field and mesocosms trials. In field trials, leaf density of flowering rush was reduced 99% and 92% at eight weeks after initial treatment (WAIT) in years one and two, respectively, while hardstem bulrush leaf density was not affected. In mesocosms, flowering rush and hardstem bulrush were exposed to repeat submersed injections of the contact herbicides diquat, endothall, copper, carfentrazone-ethyl, and flumioxazin. Endothall reduced aboveground biomass of flowering rush by 69% compared to reference plants at eight WAIT; the other herbicides did not affect aboveground biomass of flowering rush. Diquat reduced belowground biomass by 77% compared to reference plants at eight WAIT while the other herbicides had no effect. None of the herbicides tested in mesocosms affected above or belowground biomass of hardstem bulrush when compared to non-treated reference plants at eight WAIT. Future studies should investigate concentration exposure time requirements of endothall and diquat for flowering rush control.