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Glyphosate Gives Timely Boost to Pre-em Black-grass Control

Including a modern glyphosate with the pre-emergence wheat herbicide application can improve black-grass control by as much as 40%, reveal recent Agrii trials.

Conducted as part of the company’s comprehensive integrated black-grass management work, the controlled trials involved a Suffolk crop of Oakley with an untreated black-grass population of 481 plants/m2

Roundup was included in the pre-em treatment programme to tackle black-grass continuing to emerge in the seedbed ahead of early October drilling following late-September stale seedbed control with glyphosate.

Across 12 different modern residual programmes, its addition gave an average improvement in black-grass control from the pre-em applications alone of a good 15%, with gains of over 20% recorded in five cases and over 30% in three (Figure).

Figure: The effect including glyphosate with various pre-emergence programmes 

Source: Agrii

“Once black-grass starts to chit it keeps on coming through,” pointed out Agrii trials manager, Steve Corbett. “As in politics, a week can be a long time with black-grass germination. What’s more, cultivation only really serves to transplant the seedlings. And most pre-ems have a very limited impact on already-emerged weeds.

“Adding glyphosate, though, gives a very valuable extra string to the seedbed management bow; especially so if workloads or the weather mean there’s a delay of more than a few days between the final pre-planting spray and drilling. It also adds much-needed extra flexibility to the whole establishment process, allowing an extra black-grass hit without any further drilling delay.”

Based on his extensive black-grass trials experience, Steve Corbett advises growers with black-grass problems to get in at least two, if not three, cycles of glyphosate control ahead of planting this autumn, with the last spray as close to drilling as possible. As a matter of course, he suggests everyone inspects their seedbeds very closely immediately ahead of drilling, strongly advising an appropriate glyphosate is added to the pre-em mix wherever any weed growth can be seen.

“Failing to treat emerged black-grass in the seedbed is like playing Russian Roulette,” he insisted. “As many growers have found to their cost in recent seasons, with such limited post-em control options it can easily mean having to spray-off the entire crop later on.

“It’s important to use a highly active glyphosate that is both approved for pre-emergence use and widely compatible with current pre-em chemistry. Make sure you use the right spray nozzle too. Medium-fine droplets give the best coverage of very small target leaf areas. So it’s not surprising our Stow Longa studies show significant black-grass control benefits from nozzles that produce them as opposed to larger droplets.

“The pre-em spray must, of course, be applied before there’s any chance of crop emergence,” added Steve Corbett. “But then for the best control I always like to see pre-ems going on within two or three days of drilling anyway.”