Diquat bid to treat ryegrass

EXCLUSIVE Cally DupeCountryman
Mature annual ryegrass in barley.
Camera IconMature annual ryegrass in barley. Credit: Nicole Baxter/GRDC

A new pilot project investigating the feasibility of using diquat for crop-topping barley has been launched in WA to potentially reduce growers’ reliance on glyphosate for weed seed control.

Grains Research Development Organisation recently funded a $150,000, two-year pilot project investigating the use of diquat to control ryegrass in barley crops.

Diquat is registered for pre-harvest crop desiccation in a range of crops, including barley, but glyphosate is the preferred herbicide for ryegrass control.

Perth-based Synergy Consulting WA will carry out the project with subcontractors Lamond & Co and Farmanco, which includes replicated, small-plot trials in three different climatic and agronomic environments in WA.

The project was launched in July and will run until June 30 to allow for at least two seasons of data collection.

Grains Research Development Organisation crop protection manager – west Georgia Megirian.
Camera IconGrains Research Development Organisation crop protection manager – west Georgia Megirian. Credit: GRDC

It is hoped the project could give WA farmers another tool to manage late-season annual ryegrass, by validating the use of pre-harvest application of diquat to maximise weed seed set control of annual ryegrass in barley.

WA farmers currently harvest weed seed control tactics — including windrow burning — or crop top with glyphosate for dessication and ryegrass control.

However, this project will explore diquat for its weed seed control potential and not for the effectiveness of dessication.

GRDC crop protection manager (west) Georgia Megirian, right, said it was vital farmers had effective tools for late-season annual ryegrass management.

“Changes in farming systems, crop management decisions and climate variability has influenced the behaviour of annual ryegrass — one of the most serious and costly weeds of annual winter cropping systems in southern Australia,” she said.

Ms Megirian said it pre-harvest applications of diquat appeared to tackle weeds and limit weed seed viability. But she said there had been limited development of effective guidelines for its use in this context.

The GRDC project comes nearly two years after Australia’s biggest grains handler, CBH, moved to safeguard the then-burgeoning feed barley trade by introducing a new segregation for feed barley with a pre-harvest application of glyphosate.

CBH feared a growing trend among farmers to treat maturing feed barley crops with glyphosate was a serious threat to then-booming exports.

At the time, CBH told growers it had a responsibility to protect and maintain market access and didn’t believe this was possible in sending feed barley treated with glyphosate before harvest to China.

Ms Megirian said annual ryegrass was problematic to manage, with increasing reports of staggered germination and changes in dormancy patterns.

She also said ryegrass had a propensity to develop resistance to many broad-spectrum and selective herbicides.

“Current strategies relying on pre-seeding and early emergence management tactics will not maintain a low annual ryegrass weed seed bank indefinitely,” Ms Megirian said.

“There is an opportunity to assess the effectiveness of diquat for annual ryegrass weed seed control and to attempt to develop clear management guidelines for achieving consistent annual ryegrass seed set control while quantifying any potential adverse impacts to barley grain yield and quality characteristics.”

Grain Industry Association of WA barley council chair Lydon Mickel, who farms at Esperance, welcomed the project.

He said it was important to examine alternatives to glyphosate to “avoid herbicide resistance issues” and cater for markets that did not want glyphosate used in crops.

“I hope this work continues to support the use of diquat as another option for preharvest dessication and ryegrass control,” Mr Mickel said.

“Given the current activity in the marketplace and discussion about glyphosate, this is probably well-advised.”

Mr Mickel said both glyphosate and diquat were “extremely important” to WA grain farmers and neither should be phased out completely.

“If we were to lose glyphosate it would have a massive impact on the farming systems we are using in WA,” he said.

“We have a lot of lighter soil types and no-tillage farming has allowed us to improve yields and avoid wind erosion.”

To find out more about beating crop weeds, visit WeedSmart ‘Big 6’ at weedsmart.org.au/the-big-6/.

WeedSmart is the ‘single industry’ multi-channel platform for information on combating cropping weeds and herbicide resistance in Australia.

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