Use full rate to prolong life

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With chemical weed control relying on only six modes of action across Australia, prolonging the useful life of current herbicides is critical.

Dr Roberto Busi with wheat samples in a glasshouse.

Australian Herbicide Resistance Initiative (AHRI) postdoctoral fellow Dr Roberto Busi examines wheat samples in a glasshouse at the University of Western Australia.

Australian growers have a better chance of achieving sustainable use of the recently released pre-emergent herbicide Sakura® if full label rates are used on annual ryegrass populations.

Registered for use in Australia in 2012, Sakura® (pyroxasulfone) is a Bayer CropScience product for controlling annual ryegrass, including populations with resistance to several herbicides.

In a world-first, researchers at the Australian Herbicide Resistance Initiative (AHRI) examined the potential for ryegrass to evolve resistance to Sakura® before it was released commercially in Australia.

The research showed that cutting rates of Sakura® significantly increases the risk of ryegrass developing resistance to the new herbicide.

Given the high level of resistance to multiple herbicides that has already developed in ryegrass populations across Australia, it is critical that full rates of Sakura® are used so that ryegrass can be controlled effectively in cropping systems.

Close-up photo of ryegrass head

To maintain its useful life it is critical that full-label rates of the recently released herbicide Sakura® are used to control ryegrass in cropping systems.

PHOTO: Alanna Matsen

Herbicide Houdini

Ryegrass is renowned for its capacity to evolve herbicide resistance due to several in-built genetic mechanisms that enable the plant to stay one step ahead of chemicals used to control it.

Ryegrass plants are prolific pollen producers, which means the genetic mechanisms conferring herbicide resistance can move easily between plants. Thus, ryegrass populations can quickly accumulate and stack herbicide-resistance traits.

The AHRI study demonstrated that ryegrass populations developed resistance to Sakura® after only three years of low application rates. More alarming was the fact that these resistant plants then progressively evolved cross-resistance to Boxer Gold® (Groups J and K).

The secret to slowing herbicide resistance is to keep ryegrass populations low and always use full label rates. An integrated approach using the full label rate of Sakura® and rotating it with other herbicides while also using crop competition and harvest weed seed control will reduce the risk of resistance and prolong herbicide efficacy.

Harvest weed seed control can be used to control any ryegrass plants that survive Sakura® treatment, stopping these plants from contributing to the ryegrass weed seedbank. In the following season, pre-sowing knockdown with glyphosate and/or paraquat will help reduce ryegrass further.

It is important to remember that Sakura® is just another herbicide and careful management will be required to maximise its efficiency and sustainability in Australian cropping systems.

Cutting rates below the recommended label rate and over-reliance on Sakura® will shorten the herbicide’s life significantly. Full rates and integrated weed management will prolong its life.

More information:

Dr Roberto Busi,
08 6488 1423,

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GRDC Project Code UWA00146

Region West