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Autumn hit to get better ryegrass control

Agronomy Issues
21.08.2020
Ryegrass seed head above wheat

Growers tackling difficult ryegrass weed issues could make a real inroad into managing populations with an integrated approach this autumn.

Trials at the Syngenta Doncaster Ryegrass Innovation Centre have shown repeated years of good success using a combination of autumn cultivations, increased crop competition and herbicide programme timings, reported Syngenta grass weed specialist, Andy Cunningham

Andy Cunningham

Ryegrass seed dormancy tends to play less of a role in dictating germination timing, compared to black-grass, he pointed out, but growers should still take note and potentially adjust cultivation options and herbicide programmes if required. 

Find out more about ryegrass control tips and advice

Just like the black-grass scenario this season, where ryegrass seed heads matured early, during the high temperatures of early June, autumn dormancy is likely to be low. However, later maturing spikelets, when conditions had turned cool and wet, would be more likely to produce seed with a relatively higher dormancy.

“It will be more of a challenge this season, where there is a mixture of high and low dormancy seed in the same field or across the farm,” he warned.

“But in general ryegrass dormancy is short-lived, so there is still good opportunity to take action in the autumn.”

Andy’s trials at Doncaster over recent seasons revealed 80 - 99% of the site’s ryegrass weed seed germinated by the end of November - highlighting the crucial importance of autumn control strategies. “We have also seen that autumn germinating Italian ryegrass - the more problematic weed than perennial ryegrass - can produce 23x more seed return, compared to spring germinating plants.”

Cut multiplication

Ryegrass can have a greater yield effect and higher rates of multiplication, compared to black-grass. However, trials at Doncaster have shown it can itself be effectively out-competed by vigorous autumn crop growth. Successive seasons’ work has shown hybrid barley can reduce the number of ryegrass tillers per plant by 25%, compared to a wheat crop or conventional barley at the same seed rate.

Ryegrass seed head

Furthermore, the number of ryegrass seed heads could be as much as halved in hybrid barley, with a higher proportion of seed heads remaining below the crop canopy – thus producing fewer viable seeds. Andy’s monitoring of light levels in the crop have shown over 40% more light can be intercepted by hyvido barley, compared to a wheat crop.

Syngenta research has shown that growing hybrid barley in conjunction with any of the pre and post emergence combinations trialled could eliminate ryegrass growing in the crop.

Results with hybrid and conventional barley, in conjunction with pre-em Defy + flufenacet/pendimethalin, took out all ryegrass. In autumn-sown wheat, a follow-up with a post-em application of Axial Pro also delivered complete ryegrass control to eliminate seed return.

Pre-em timing

With the typically rapid and even emergence of ryegrass seedlings, the most consistent results have been achieved with pre-em applications as soon as possible after drilling, advocated Andy.

Ryegrass emerging

“We know that rainfall and soil moisture do have an impact. But the best efficacy has consistently been achieved with pre-em application immediate after drilling,” he advised. “With the increasing trend to extreme weather events that could compromise later application, trials show it’s better to get a pre-em on early, than risk waiting for better weather that never arrives!”

Ryegrass innovation

Syngenta’s Ryegrass Innovation Centre in Yorkshire is situated in an epicentre of problematic ryegrass issues. The site was specifically created to generate insights into the short- and long-term impact on grass weed control and yield from cultural and chemical controls and application methods.

Now going into its third year of trials on the same site, it offers a vast matrix of results and combinations to tease out grass weed solutions that work in practice.

Find out more ryegrass agronomy solutions and trials results from the Ryegrass Innovation Centre here.