NOTES Combinations of diquat and carfentrazone- ethyl for control of floating aquatic plants

Flowering rush (Butomus umbellatus l.) is a rapidly spreading invasive aquatic plant in the northern United states. Introduced from eurasia, it grows as an emergent plant along shorelines and as a submersed plant in deeper water of lakes and rivers. Because submersed flowering rush grows in fluctuating water levels, management of this plant has been inconsistent and unpredictable. Two small-scale experiments were conducted to evaluate contact herbicide efficacy on the submersed form of flowering rush from two triploid populations, one from Minnesota and one from Idaho. In the first experiment, various concentrations and exposure times of diquat, endothall, and flumioxazin were applied to Minnesota flowering rush. In the second experiment, concentration–exposure time relationships were investigated for flumioxazin against Idaho flowering rush. One treatment of endothall was used to compare flumioxazin, a newly registered compound, with an older chemistry. Results of both experiments showed that contact herbicides are effective against flowering rush. although flumioxazin (200 μg ai l-1) did not significantly reduce shoot biomass for exposure periods of 12 or 24 h, concentrations of diquat (370 μg ai l-1) for exposure times of 6 and 12 h, and endothall (1500 and 3000 μg ai l-1) for exposure times of 12 and 24 h reduced shoot biomass of Minnesota submersed flowering rush by >70%; however, these treatments did not significantly impact root biomass. lateral rhizome buds, which serve as a source of annual reinfestation, were found in all treatments. Concentrations of flumioxazin (400 μg ai l-1) and endothall (3000 μg ai l-1 ) for exposure times of 24 h controlled Idaho submersed flowering rush by successfully reducing shoot and root biomass by >70%. application strategies for complete control of triploid flowering rush shoots and roots with contact herbicides may require repeat applications and/or combinations with each other and systemic herbicides. Further evaluation of herbicides for controlling triploid as well as diploid flowering rush is warranted.