Mechanical control of flowering rush (Butomus umbellatus)

Authors: TURNAGE, GRAY - Mississippi State University; Madsen, John; WERSAL, RYAN - Minnesota State University; BYRD, JOHN - Mississippi State University

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2019
Publication Date: 4/17/2019
Citation: Turnage, G., Madsen, J.D., Wersal, R.M., Byrd, J.D. 2019. Mechanical control of flowering rush (Butomus umbellatus). Invasive Plant Science and Management. 12:120-123.

Interpretive Summary: Flowering rush (Butomus umbellatus) is an invasive plant species with an adaptive growth form capable of growing in aquatic and wetland habitats. This requires resource managers to control flowering rush in a variety of environments and as such resource managers need multiple control strategies as one control methodology may not work in multiple settings. In most aquatic environments, flowering rush is controlled with the use of herbicides labeled for use in aquatic sites, however, in some locations herbicides may be prohibited or may not be a feasible control option due to high rates of water exchange. In areas such as these, mechanical control in the form of clipping and harvesting may be a suitable control option if done every two weeks. Monthly and bimonthly clipping had varying degrees of success for control of flowering rush tissues and propagules. Timing of clipping should be done such that fish species are not spawning in sites infested with flowering rush. Clipping is likely to dislodge flowering rush propagules from the hydrosoil that could then float away to infest new sites; areas targeted for clipping would need to have floating booms placed around them to capture floating propagules for later disposal.

Technical Abstract: Flowering rush (Butomus umbellatus L.) is an invasive aquatic and wetland plant species that is capable of rapidly outcompeting native plant species for resources which, over time, can lead to reduced biodiversity at infested sites. Flowering rush is also a hindrance to human uses of aquatic resources due to its ability to form large monotypic stands in emergent and submersed sites that are used for recreational (boating, fishing, and skiing) and agricultural (irrigation canals) purposes. In many infested sites, flowering rush is controlled with herbicides labeled for aquatic use. However, in some locations, herbicides may not be in contact with the plants long enough to provide control or the use of herbicides is prohibited. Resource managers need alternative control (biological, physical, or mechanical) options in sites where chemical control if not feasible. The use of mechanical control (clipping and harvesting) is a common practice for the management of some aquatic plant species. Four clipping protocols (biweekly, monthly, bimonthly, and once per growing season) were evaluated over two years (2016 and 2017) and compared with a chemical control protocol (0.19 ppmv ai diquat applied in two consecutive months). Only the biweekly clipping and harvesting gave consistent control of flowering rush biomass and propagules. Diquat along with monthly and bimonthly clippings gave varying degrees of flowering rush control. Clipping once per growing season did not control flowering rush when compared to reference plants. While clipping every two weeks (biweekly) controlled flowering rush propagules it is unlikely that this method will be used as a stand-alone control option due to the slow speed of harvester boats and the potential these boats have to spread flowering rush propagules to more sites. However, clipping could be used as part of an integrated control strategy for flowering rush.