Western Australia
April 18, 2016

As well as providing a break to the season, significant early rainfall has provided Western Australian grain growers with the perfect opportunity to hunt down and eradicate glyphosate resistant weeds.

Conditions are ripe for employing the ‘double knock’ technique, where two weed control tactics with different modes of action are used to ensure that any weeds that survive the first application are killed as a result of the second application.

This is the message from Australian Herbicide Resistance Initiative (AHRI) communications leader Peter Newman, who encourages growers to take a zero-tolerance approach to weeds that survive applications of the important knockdown herbicide glyphosate.

(Click here for more details of a grower who has taken this approach)

“Most of the grainbelt has received enough rain in recent weeks to encourage a good germination of winter weeds including annual ryegrass, and many growers will spray glyphosate to control them,” Mr Newman said.

“This year may be a good opportunity to find out where any glyphosate resistant weeds are, if you use a knockdown soon but don’t seed for a few weeks.

“Glyphosate resistant weeds can be very hard to find as growers often spray and then seed crops soon after, especially in years where breaking rains are received later in the season.

“They say you can’t manage what you can’t measure, and in those cases we may not be able to measure what we can’t see.”

Mr Newman said Grains Research and Development Corporation (GRDC) supported surveys in WA had indicated escalating weed resistance to herbicides including glyphosate, and it was likely some weeds would have survived initial knockdown sprays.

“Growers should act immediately and use alternative knockdown herbicides to control the weeds and prevent them setting seed,” he said.

“For the longer-term, they should develop a plan to drive down the weed seedbank using chemical, cultural and mechanical methods.”

Mr Newman said the double knock technique – which in most cases involved full rates of glyphosate followed by full rates of paraquat or combined paraquat and diquat (Spray.Seed®) about two to 10 days later – was an ideal tool to help growers prevent glyphosate resistance from occurring.

“The best time to start using double knock is before you have glyphosate resistance,” he said.

“However, double knock is still a good option for growers with confirmed glyphosate resistance.”

Mr Newman said growers who found surviving weedy patches should have weed samples tested for herbicide resistance through a ‘Quick-Test’ service (www.plantscienceconsulting.com).

He also said glyphosate resistant ryegrass was not the end of the world and could be managed by driving down the weed seed bank.

“John Flannagan, a grower near Mullewa in WA’s northern grainbelt, is an example of someone who has successfully managed glyphosate resistant annual ryegrass by jumping hard and early on the problem,” he said.

(Click here for more details about how Mr Flannagan has managed glyphosate-resistant annual ryegrass)

To support growers and their advisers in driving down the weed seed bank, Mr Newman encouraged subscription to AHRI Insight at www.ahri.uwa.edu.au and making use of the practical information available via the WeedSmart website, www.weedsmart.org.au, as well as the GRDC Integrated Weed Management Hub at www.grdc.com.au/IWMhub.

The GRDC has a $1.5 million annual investment in the AHRI, based at The University of Western Australia. AHRI is a research leader in herbicide resistance and its management in cropping systems.

Analysis shows that GRDC investment into the area of herbicide resistance over the past 25 years has returned a benefit-to-cost ratio of $3.50 for every dollar invested.

Website: http://www.grdc.com.au

Published: April 18, 2016