Response of fanwort (Cabomba caroliniana) to selected aquatic herbicides in New Zealand

Fanwort (Cabomba caroliniana A. Gray, also known as cabomba) is an obligate submersed macrophyte native to the southern United States and Central and South America that has naturalized in the eastern United States, Canada, and various countries in Europe, Asia, and Oceania. It has been cultivated in New Zealand as an aquarium plant for at least 30 yr, but until recently (2009) had not naturalized. Fanwort is now declared an Unwanted Organism in New Zealand and as part of incursion response planning, effective management responses are required to achieve eradication. In this study we conducted herbicide trials on fanwort in containment using the herbicides carfentrazone, endothall, flumioxazin, and triclopyr. All four herbicides reduced fanwort biomass; however, with all herbicides viable plant material remained, indicating the potential for rapid regrowth after treatment, and a high degree of uncertainty of outcome where the herbicides are to be used for the management of field populations. None of the herbicides are recommended for use in eradication programs on fanwort without a clear understanding that multiple applications will likely be required, and there is a degree of uncertainty regarding the level of efficacy that can be achieved.