LANDHOLDERS in North Queensland have a very narrow window of opportunity to make an effective strike against the spreading and highly competitive weed Navua sedge.
Impacted producers are urged to closely follow a control technique developed and proven over several years in the northern tropics, and to act immediately to enable two applications of registered herbicide eight to 12 weeks apart while the weed is still actively growing.
The only selective herbicide registered for Navua sedge control in Australia is Sempra.
Trials on the properties of Daryl McLaren, Innisfail; Con Frumento, El Arish; Nev Condon near Tully; and Steve Gileppa near Ingham showed that Navua sedge is best controlled in pastures by grazing or slashing infested pastures two to three weeks before a first spray of Sempra – reducing pasture and weed biomass and allowing time for the weed to re-shoot – to provide the optimum target for that first spray.
No grazing or cutting for forage is then allowed for 10 weeks after spraying, to comply with residue withholding periods and National Vendor Declarations (NVD).
The pasture is then grazed or slashed again, before a second follow-up spray of Sempra – 8-12 weeks after the first – to control new germinations.
Nufarm research and development officer in North Queensland Nicholas Matthews has been conducting trials with impacted producers since being alerted to the problem in 2010 by Dave Doolan, GF Rural, Innisfail-Tully.
On the basis of five years’ trial work for both its efficacy against Navua sedge and to determine the necessary withholding period, Sempra was registered for controlling this weed in late 2015.
Mr Matthews said one North Queensland council was already actively working to slow the spread of Navua sedge and to stamp it out from public and private lands, but that a wider more collaborative approach was needed in other municipal regions.
“This weed has the potential to put people out of business.
“Two sprays of Sempra 10 weeks apart, combined with good grazing management and vigorous pasture growth, have provided very good control of any Navua sedge present at application, significantly reducing the weed population and seed set.”
He urged producers not to risk their livelihoods by using any unregistered halosulfuron products.
Mr Matthews also pointed out that some cattle deaths had resulted from not following the recommended grazing strategy, so it was imperative to adhere closely to label advice.