Water weed management with the new aquatic herbicides flumioxazin and florpyrauxifen-benzyl

Invasive aquatic plants cause significant socio-economic and environmental impacts to Australia’s precious freshwater resources. Most of these aquatic weeds are difficult to manage due to a lack of effective and economical control tools. In 2021, the contact herbicide flumioxazin (Clipper herbicide) was registered by the Australian Pesticides and Veterinary Medicines Authority for control of aquatic weeds. The systemic herbicide florpyrauxifen-benzyl (ProcellaCOR) has been used for aquatic weed control in the USA since 2018 and was registered in Australia March 2024. Both herbicides are used at low application rates and have a favourable environmental profile. Therefore, they pose a low risk of non-target damage when dosed and applied appropriately for target weeds and the site-specific environmental conditions. Lab trials were carried out with flumioxazin and florpyrauxifen-benzyl to determine control efficacy of established and emerging aquatic weeds with foliar or in-water applications. Subsequent field trials tested the herbicides in management scenarios to measure control efficacy in a range of environmental conditions and situations. Flumioxazin provided excellent control of Amazon frogbit, kidney-leaved mudplantain, hairy water hyssop (Bacopa lanigera), cabomba, Mexican water lily and water lettuce. It also controlled sagittaria, both submerged and emergent, but the results can be variable. Florpyrauxifen-benzyl efficiently controlled parrot’s feather, Rotala rotundifolia, cabomba, water hyacinth and sagittaria. Experiments also demonstrated that flumioxazin and florpyrauxifen-benzyl cause limited to no damage to many native aquatic plants, especially valuable emergent plants along the shoreline. Both herbicides gave excellent control if applied as foliar or in-water (injection) application, depending on situation and target weed. Together, these two new herbicides will greatly aid the efficient management of many established and emergent aquatic weeds in Australia. Ongoing research will investigate control efficacy for further target weeds, impacts on non-target aquatic plants, efficient application techniques and treatment strategies.