Ryegrass management in the HRZ relies on a stacked approach

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18 October 2021, AU: Annual ryegrass in the high-rainfall zone (HRZ) is as competitive and damaging as in lower-rainfall environments, with each ryegrass plant reducing cereal yield potential by about 0.3 per cent, according to recent research undertaken to develop integrated and profitable weed management strategies.

The research conducted by the University of Adelaide, Southern Farming Systems and MacKillop Farm Management Group through Grains Research and Development Corporation (GRDC) investment, showed there is no benefit to tolerating more weeds in the HRZ than in other environments. Previously questions had been raised about whether the higher yielding environment of the HRZ could tolerate the presence of more weeds.

However, it has been shown that both crops and annual ryegrass grow vigorously, and the yield loss due to weeds is similar in both low and high-rainfall zones.

James Manson, Senior Research and Extension Officer, Southern Farming Systems, said managing annual ryegrass in the HRZ has been a significant challenge for many years, but this has increased through the prevalence of herbicide resistance.

“In the HRZ, annual ryegrass germinates throughout winter into spring, which challenges the ability of early season herbicide strategies to control it,” Mr Manson said.

“The unique environment of the HRZ requires an integrated approach to weed management where multiple tactics are stacked over several seasons to have a greater chance of success.

“The economic benefits of additional weed control tactics are less in lower yielding years but increase in higher yielding years. The benefit of increased herbicide expense and weed control may not be captured every year because the season has a greater effect on yield than weed pressure. Instead, the benefits of improved weed control accumulate over time, paying off given the right conditions.”

Robust pre-emergent herbicide strategies, crop competition and double breaks are important tools for reducing the seed production of annual ryegrass in the HRZ.

Harvest weed seed control is less effective than in other regions due to the staggered ryegrass maturity in the HRZ, but still plays a very important role when integrated with other tactics.

Stacking these weed management tactics are essential for long-term control of annual ryegrass in the HRZ.

A new Managing Annual Ryegrass in the High Rainfall Zones of Victoria and South Australia and Tasmania publication has been developed to disseminate the research findings.

GRDC Growers Relations Manager – South, Randall Wilksch says the new publication provides practical information gained from years of research and industry experience.

“The booklet combines information from several GRDC investments into one consolidated resource focussing on clear messages for growers and advisers on combating annual ryegrass.”

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