Fears that ryegrass had developed resistance to mechanical management techniques such as chaff carts have been investigated by a Grains Research & Development Corporation (GRDC) supported research project.

Renowned for its resilience, ryegrass looms as the most stubborn of Australia’s $3 billion weed threats and its resistance to herbicides has driven the use of chaff carts, which catch and remove weed seeds at harvest.

Research by David Ferris at the University of WA-based WA Herbicide Resistance Initiative (WAHRI) has now established that these techniques are not yet being negated by ryegrass’ infamous ability to develop resistance to controls.

To determine if ryegrass had adapted to chaff carts, Mr Ferris collected seed from paddocks near Wongan Hills which had undergone seed-catching at harvest for eight consecutive years and from adjacent paddocks, on neighbouring properties, where seed catching had never occurred.

Plants from those seeds were then studied for traits which would allow them to avoid collection from chaff carts, such as reduced height and greater seed shattering before harvest, but none of these adaptations were found.

The results suggest that after eight years, chaff-carts are likely to remain as effective at collecting ryegrass as when first introduced.

"We know that ryegrass has an enormous amount of genetic variability, including

traits that could give resistance to seed-catching if selected," Mr Ferris said.

"The key message from this WAHRI study is that although chaff cart resistant ryegrass might occur over an extended period of time, it has not occurred at Wongan Hills in the past eight years.

"While adoption of chaff carts is encouraged, it is important to maintain a diversity of weed control options to minimise the development of resistance to any of them," he said.

WAHRI is supported by growers and the Federal Government via the GRDC’s Crop Protection Program, which encourages cost-effective, robust, environmentally sound solutions to manage current and potential crop protection threats.