Efficacy of halosulfuron-methyl in the management of Navua sedge (Cyperus aromaticus): differential responses of plants with and without established rhizomes

Abstract

Navua sedge is a creeping perennial sedge commonly found in tropical environments and is currently threatening many agroecosystems and ecosystems in Pacific Island countries and northern Queensland, Australia. Pasture and crop productions have been significantly impacted by this weed. Efficacy of halosulfuron-methyl on Navua sedge plants with and without well-established rhizomes was evaluated under glasshouse conditions. Halosulfuron-methyl was applied to plants with establishes rhizomes that had been mowed and pre-flowering and flowering growth stages; while plants without established rhizomes were treated at seedling, pre-flowering and flowering growth stages. At each application time, halosulfuron-methyl was applied at four dose rates of: 0, 38, 75, and 150 g ai ha−1. Mortality of 27.5%, 0%, and 5% was recorded in rhizomatous Navua sedge when treated with 75 g ai ha−1 of halosulfuron-methyl at the mowed, pre-flowering stage and flowering stages, respectively. At 10 wk after treatment (WAT), there were no tillers in surviving plants treated at any of the application times. By 16 WAT, the number of tillers increased to 15, 24, and 26 in mowed, pre-flowering and flowering stages, respectively. Although halosulfuron-methyl is effective in controlling the above ground growth, subsequent emergence of new growth from the rhizome confirms the failure of the herbicide to kill the rhizome. Application of 75 g ai ha−1 of halosulfuron-methyl provided 100% mortality in plants treated at seedling and pre-flowering stage, and 98% mortality when treated at flowering stage in non-rhizomatous plants. A single application of halosulfuron-methyl is highly effective at controlling Navua sedge seedlings but not effective at controlling plants with established rhizomes.

Growth of the invasive Navua sedge (Cyperus aromaticus) under competitive interaction with pasture species and simulated grazing conditions: Implication for management

“…It is usually recommended to apply these herbicides at least three times a year to achieve >90% population reduction, but such a reduction is rarely achieved by farmers using Halosulfuron Methyl due to the cost (Shi et al, 2021). Also, herbicide applications have been known to be temporary measures with minimal impact on subterranean rhizomes and dormant seeds which are the prime reason for Navua sedge's resurgence and contribution to its spread (Chadha et al, 2022; Vitelli et al, 2010). Moreover, after the herbicide application of Halosulfuron Methyl, pastures are restricted for cattle to graze upon (withholding period; spelling) for at least 10 weeks, which also imposes a significant impact and financial cost on beef and dairy enterprises.…”

“…Equally, in Queensland, current chemical control options are unable to reduce the recurrence and spread of the weed (Vitelli et al, 2010;Vogler et al, 2015). The only registered herbicide against Navua sedge in Australia is Halosulfuron Methyl (e.g., Sempra ® ); general broad-spectrum herbicides such as Glyphosate and Paraquat, are also used for control of Navua sedge (Chadha et al, 2022;Vitelli et al, 2010), but these herbicides have been found to be of limited success. It is usually recommended to apply these herbicides at least three times a year to achieve >90% population reduction, but such a reduction is rarely achieved by farmers using Halosulfuron Methyl due to the cost (Shi et al, 2021).…”

Effect of Rhizome Fragment Length and Burial Depth on the Emergence of a Tropical Invasive Weed Cyperus aromaticus (Navua Sedge)

“…Studies conducted on C. aromaticus show that sequential applications of herbicide are required for the control of this species [ 2 , 7 ], and currently only one herbicide, halosulfuron-methyl (Sempra), is registered for its control in pastures. However, a single application of halosulfuron-methyl affects the aboveground foliage, but does not kill the rhizome [ 8 ]. In addition, relying on and using one herbicide continuously will seriously increase the chance of herbicide resistance [ 9 , 10 ].…”