Control of Cabomba caroliniana with flumioxazin: control efficacy and the effect of environmental factors

Cabomba caroliniana A.Gray (Cabombaceae), native to South America, has become a highly invasive species of water bodies worldwide where it has been introduced. Cabomba’s tendency to displace native aquatic plants poses a threat to native biodiversity. Cabomba has now established in most states in Australia and with only few viable control options management efforts are directly hampered. Currently only one herbicide (carfentrazone) is registered in Australia for the control of cabomba in non-flowing water. Based on high treatment costs and the lack of options in flowing water makes the management of larger infestations impossible. The efficacy of the herbicide flumioxazin to control cabomba and the effects of environmental factors (pH and shading) on herbicide performance were tested through a series of experiments. Dose-response relationships (5 – 400 ppb active ingredient (a.i.)) demonstrated that cabomba is highly sensitive to Flumioxazin. Excellent control (96% of biomass) of cabomba was achieved at 5 ppb a.i. and complete kills were observed when flumioxazin was applied to the water column at rates ≥ 10 ppb. The native Vallisneria nana was not visually affected by flumioxazin at such low rates. The efficacy of flumioxazin is reportedly linked to the pH of the water (rapid breakdown occurs at high pH levels; ~15 min half-life at pH 9) and light penetration, but we found no evidence of an effect of pH or shading on efficacy to control cabomba. Later trials confirmed that cabomba is effectively controlled even if exposed to the herbicide for only 15 minutes. Flumioxazin promises to be an efficient and economically viable tool for the control of cabomba in Australia. The high susceptibility of cabomba means application rates can be reduced to a level that the herbicide becomes practically species specific. Future research will investigate improved delivery mechanisms and test a wider range of native species to get a better understanding of non-target damage.