Control of delta arrowhead (Sagittaria platyphylla) in Australian irrigation channels with long exposure to endothall dipotassium salt during winter

Delta arrowhead [Sagittaria platyphylla (Engelm.) J.G. Sm.] is an emergent, aquatic plant, originating from North America, which has invaded aquatic environments in Australia. The plant is particularly problematic in southeast Australia, where it invades earthen irrigation channels and drains. Hydraulic capacity is subsequently reduced, leading to a reduction in the efficiency of water delivery. Options for controlling delta arrowhead in irrigation channels and drains are currently underdeveloped. Previous trials have indicated that a potential control option is to treat irrigation channels that hold standing water during temperate winter conditions with the contact herbicide endothall. This article reports on a field experiment to determine the dose–response relationship for endothall dipotassium salt and delta arrowhead. A 3-wk exposure period of endothall dipotassium salt to delta arrowhead during winter at 5 mg ai L 1 provided 69% biomass reduction of the emergent petiolate growth form and 92% biomass reduction of the submersed phyllodial growth form 6 wk after treatment (WAT). Control remained evident at 15 WAT; however, by 26 WAT differences between treatments were not detected. This reduction in biomass confirms endothall dipotassium salt to be a useful tool to reduce delta arrowhead biomass during the spring irrigation period.