Herbicide Options for the Management of Navua Sedge ( Cyperus aromaticus ) Plants Established through Seeds

Navua sedge is a difficult-to-control perennial sedge in north Australian farming systems, including fallow fields, pastures, and along roadsides and fencelines. A set of pot trials were conducted to evaluate the performance of different herbicides when used alone or in mixtures on different sizes of Navua sedge plants, and the performance of different adjuvant treatments on the rainfastness of halosulfuron-methyl. Glyphosate at 1080 g·ha −1 , halosulforon-methyl at 49 g·ha −1 , and paraquat at 600 g·ha −1 provided complete control of Navua sedge at the 6-leaf stage. Azimsulfuron at 20 g·ha −1 resulted in 18% and 39% survival of the 14 to 18 leaf stage and 60–70 leaf stage plants, respectively. Compared with the nontreated, this herbicide treatment suppressed plant biomass by 99.6% and 93%, respectively, and the surviving plants did not produce seed heads. A sole application of azimsulfuron, glyphosate, or halosulfuron-methyl was not effective on very large plants (140–150 leaf stage; 40–42 cm tall) of Navua sedge. However, a mixture of any two herbicides resulted in the complete control of Navua sedge. Compared with the currently used adjuvants at 0.5 to 1% concentrations, the use of non-ionic adjuvants at high concentrations (i.e., 2% ActivatorTM, HastenTM, and UptakeTM) improved the rainfastness of halosulfuron-methy when applied at 49 g·ha −1 on Navua sedge. This study identified effective herbicide treatments (e.g., azimsulfuron-based combinations) for the management of large plants of Navua sedge.