Experts share winning strategies for the black-grass battle

Integrated management is the best solution to tackling the increasing threat from black-grass: the overwhelming conclusion from industry experts gathered at a Bayer CropScience Black-Grass Task Force conference in Peterborough.

Taking delegates from the theoretical to the practical, the experts shared their knowledge and experience of how best to control this difficult grass-weed.

Craig Knight, a PhD student from the University of Warwick, is in year three of a four-year study exploring evolutionary dynamics of black-grass herbicide resistance. He explained his preliminary findings.

“In 2011, resistance to an ALS inhibitor affected 43% of populations tested,” said Mr Knight. “Resistance to an ACCase inhibitor affected 100% of tested populations. In both cases enhanced metabolic resistance (EMR) is the primary mechanism. Retesting populations annually since 2011 has shown that resistance levels haven’t changed much.

“Unlike target site resistance (TSR), which is specific to a particular mode of action, cultural control provides the best method of controlling EMR black-grass.”

The point was echoed by Andrew Cotton who drew on his 40 years of field experience to demonstrate the effectiveness of stacked cultural control.

“A particularly heavy population at a farm in Buckingham demanded a complete overhaul of the rotation.

“Needing something radical, we started with three spring crops – barley, oats and Canadian red wheat, back-to-back. All naturally competitive against black-grass, when preceded by multiple stale seedbeds we gradually gained the upper hand.

“By 2013 we were able to return to winter crops: oilseed rape in 2013 and wheat this year.

“Just be careful with spring cropping to consider what chemistry is available,” Mr Cotton warned, “and of course, how it’s applied.”

That was a sentiment that formed the thrust of David Felce’s presentation.

“Up to fifty per cent of a herbicide’s control is down to accurate timing and application technique.

“But with sprayer operators under pressure to cover more acres within short weather windows increasing efficiency is a major challenge.

“It’s important to choose where those efficiencies are made carefully as some actions that improve work rates can drastically reduce application efficacy.

“If you don’t hit the target you won’t get the control,” says Mr Felce.
“Take forward speed. It has least impact on increasing output but the biggest effect on spray quality. Double the speed and turbulence increases four fold.”

“Equally, reducing water volumes, particularly at pre-emergence, can jeopardise coverage.”

Instead, growers should focus on logistics, he said. “How can you make your filling stations more efficient, for example?”

Finally, Keith Norman – technical director at Velcourt – tried to give delegates a glimpse of the future, with a summary of the company’s current research.

“Companion cropping, catch cropping and bio-herbicides are all producing promising results,” he noted.

“Avenacin is a chemical produced by oats, which appears to have allelopathic qualities. When sown alongside a wheat crop, oats consistently reduce the number of black-grass heads. We suspect the avenacin is having a suppressive effect.”

Oats are also the subject of a joint study between Agrovista and Bayer CropScience, which sees black-oats sown in autumn to crowd-out early-germinating black-grass, and then a spring crop sown in the sprayed-off residue – with the added advantage that reduced soil disturbance presents fewer opportunities for spring-germinating weeds.

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