Australia: Growers armed with triple threat against weeds in the south

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08 February 2022, Australia: Southern growers could be changing their weed management practices after results from nearly five years’ worth of trials indicate a triple threat strategy, that counters traditional methods, could produce optimal results.

Last week, the Grains Research and Development Corporation (GRDC) released a video summarising results from trials conducted by the University of Adelaide on weed management across the southern grain growing region.

This GRDC investment investigated the most effective ways to minimise the impact of weeds on crop yields in varying rainfall zones and suppress weeds throughout the growing season to reduce their seedset.

University of Adelaide’s Associate Professor of Agronomy and Weed Science, Dr Gurjeet Gill, said one of the most interesting results of the trial showed that current weed populations can cause more damage to crop yields if sowing is delayed, which has been a common management practice for weed control across the southern grain growing region.

“Commonly, southern growers have opted to delay sowing allowing a knockdown spray but our trial results have emphasised that this can backfire,” he said.

“Weeds have evolved to have later dormancy, meaning there could be very minimal weed growth at sowing and more weeds emerging anywhere from a month to six weeks after rains.”

“These later emerging weeds can compete more aggressively with late sown crops as their vigour slows down in the cooler months and significantly impact yields.”

As well as sowing earlier, Dr Gill said the trials revealed a higher seeding rate paired with optimal herbicide management also proved most effective when developing good crop competition against weeds and suppressing their seedbank throughout the season.

“Our results showed that when you double the crop seed density from 100 to 200 plants per square metre, you can potentially halve the seed set of ryegrass.”

“Even for growers in lower rainfall zones, who traditionally worry about higher seed rates impacting the quality of grain, results showed that the denser seed rates didn’t have a negative impact on yield or quality.”

Dr Gill said in both wheat and canola trials, results showed the non-chemical approaches to weed management of timely sowing and denser crop populations, paired with effective herbicide application was the triple strategy to managing weeds.

“These cultural practices proved to be extremely valuable in preserving yields when integrated with effective pre-emergent herbicides,” he said.

GRDC Manager Weeds, Jason Emms, said this project highlighted the importance of continuing to assess management strategies to ensure they were effective against the ever-evolving nature of weeds.

“GRDC is committed to investing in research to look at new ways for growers to manage weeds to help improve their profitability,” he said.

“An integrated approach to weed management, using cultural and chemical practices, is critical when it comes to tackling weeds and preserving crop yields.”

GRDC will be presenting the most up-to-date research on weed management for southern growers during the Grains Research Update series on Thursday, February 10.

The online event will focus on the latest information for herbicide management, weed recognition, and effective pre-emergent formulations and strategies to stay on top of prominent weeds.

Mr Emms said the Update series aims to build the profitability of grain growers by delivering regionally relevant, practical, farm-ready information.

“The Updates offer the latest results and information to help equip growers in their battle to control weeds in the most effective and efficient way,” he said.

“I encourage all southern growers to register for the Updates and take advantage of the questions and answer forums.”

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