May 22, 2012
Following widespread germination of weeds triggered by autumn rain, Western Australian growers must take every opportunity to use the knockdown herbicide paraquat instead of relying solely on glyphosate.
This includes using paraquat as a ‘single knock’ to control small grasses and broadleaf weeds up to the two-leaf stage or, where weeds are bigger, using a ‘double-knockdown’ of a full rate of glyphosate followed by a full rate of paraquat.
This is the message from Department of Agriculture and Food’s (DAFWA) Peter Newman, who conducts Grains Research and Development Corporation (GRDC) supported weeds research.
“We must take every opportunity to give glyphosate a rest,” he said.
“If we use only glyphosate every year for our knockdown then resistance to the world’s best herbicide is inevitable.
“Both paraquat and glyphosate are now extremely cheap so there is little argument for making cost savings by using only glyphosate.”
Mr Newman said paraquat-based herbicides worked best in controlling small weeds, and may have an advantage over glyphosate in controlling broadleaf weeds at the cotyledon stage.
“Where grasses are at the one to two-leaf stage and broadleaf weeds are at the cotyledon to two-leaf stage, paraquat products as a single knock are a great option for cost effective weed control while giving glyphosate a rest,” he said.
“But as grass weeds progress to the three-leaf stage and beyond it can get difficult to get reliable control with a single pass of a paraquat-based herbicide.
“This is where growers should consider switching to the ‘double knockdown’ technique, which not only reduces the risk of glyphosate resistance developing, but is a good way to achieve a very effective knockdown of weeds.”
Mr Newman said the ‘double knockdown’ technique involved a full lethal rate of glyphosate followed by a full lethal rate of a paraquat-based herbicide.
“These applications can be applied as closely as one day apart to allow for timely seeding of a paddock, with the ideal application time being two to seven days between ‘knocks’,” he said.
Mr Newman stressed that paraquat’s weakness was its reduced ability to control capeweed.
“For capeweed paddocks, consult your agronomist - you may choose to use the double knock technique or mix paraquat with an appropriate mixing partner,” he said.
To help growers understand and manage herbicide resistance in glyphosate, paraquat and 2,4-D, two farm advisor ‘learning groups’ have been established in WA under a national herbicide resistance project initiated by the GRDC.
Groups at Esperance and Moora are helping to design local field trials to test integrated weed management strategies to reduce the onset of herbicide resistance.
For more information about herbicide resistance, tactics to manage resistance and systems for farming, growers are encouraged to email firstname.lastname@example.org to subscribe to the new GRDC-supported quarterly e-newsletter Giving a Rats.
More information about glyphosate resistance is also available via the GRDC Glyphosate Resistance Fact Sheet at www.grdc.com.au/GRDC_GlyphosateResistance or www.grdc.com.au/weedlinks