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Black-grass-affected crops: Stick or twist?

For many growers spring black-grass control decisions now include whether to keep or spray-off crops. Abby Kellett reports.

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Black-grass-affected crops: Stick or twist? #clubhectare

While spraying-off areas of crops affected by black-grass is a tough decision, its one that more growers are now prepared to consider, according to Hutchinsons agronomists Andrew Wright and Alex Wilcox, who say a zero-tolerance approach is essential in the fight against the weed.


Concerns about the development of black-grass populations and the spread of black-grass further north and west across the UK, combined with disillusionment over the efficacy of products affected by herbicide resistance, means there is more acceptance of this zero-tolerance strategy, says Mr Wright.


See also: Late emerging black-grass a challenge this autumn


And with high dormancy in black-grass seed shed last summer there is a continued risk of fresh emergence into spring this year.


Assessing crops in the early New Year for black-grass which has survived autumn treatments is key to making an early decision which minimises the financial impact and allows more time to sow an alternative spring crop if required, says Mr Wright.


“Farmers are more inclined to spray-off affected crops to reduce seed return. I have seen fields up to 100 hectares being sprayed-off but generally farmers are spraying-off part fields.”

But there is no right answer when it comes to knowing when black-grass populations justify a glyphosate application, according to Mr Wright.


See also: Crop Walk and Talk...with Iain Sanderson


“It is a difficult decision to make and there’s no set black-grass population threshold to go by; it’s really down to individual growers.

Andrew Wright

"Some will want to spray-off areas of crops at the first sign of any surviving black-grass, while others will persevere, especially in regions where good results can still be achieved with spring herbicides, such as parts of Derbyshire and west Nottinghamshire.”

Case study: Will Atkinson, Yorkshire

Case study: Will Atkinson, Yorkshire

In response to a rise in black-grass populations and reduced Atlantis (iodosulfuron + mesosulfuron) performance, Yorkshire farmer Will Atkinson has resorted to an aerial strategy in order to map and accurately spot spray the weed.


Mr Atkinson says: “In the past, we were coming across areas of infestation even after our pre-emergence treatment. So in May we ended up driving up and down fields trying to spot spray with glyphosate and naturally some areas got missed.


“With our new approach, I am trying to take human error out of the equation.”


Now Mr Atkinson uses a drone to identify black-grass plants between September and June, using the data collected to create a map of black-grass populations for each field.


But before this can be done, Mr Atkinson must programme the drone to recognise black-grass as the target species.


See also: Yorkshire farmer looks to the skies for strategy to control black-grass


“Every weed carries its own infrared signature. Using a special piece of kit, we can lock into a weed’s infrared signature, identify what it is and find that same signature anywhere else in the field,” Mr Atkinson says.


Since the accuracy of glyphosate application is currently limited to the width of his sprayer, Mr Atkinson accepts he will always get a small amount of crop loss.


But by opting for a site-specific strategy as opposed to a blanket approach to herbicide application, he says he can significantly reduce his herbicide spend, while reducing weed seed return.


“This strategy comes with a cost in that we lose the crop which is among the black-grass. But if we want to grab the bull by the horns we have to make some difficult decisions and that includes using Round-up,” he says.

Although autumn weed control was generally effective given favourable weather and soil conditions, Mr Wilcox warns high black-grass dormancy means there is a continued risk of fresh emergence into spring.


Fields should be walked over to identify and map problem areas of black-grass ready for treatment, he advises.


"There’s got to be a zero-tolerance approach towards any patches of black-grass."


By assessing for black-grass which has survived autumn herbicide treatment throughout the coming weeks, growers can make an early decision as to whether to resort to glyphosate, says Mr Wright, who adds early assessment will minimise the financial impact and allow more time to sow an alternative spring crop if required.


“A grower may have spent £250-£300/ha on cultivation, seed and autumn herbicides plus the cost of spraying-off the affected crop.


“But by making this decision early, they could save on spring inputs and avoid potentially large crop losses and the return of black-grass seed to the seedbank,” he says.


When it comes to oilseed rape, Mr Wilcox acknowledges there is limited ability to control black-grass into spring, but insists it must be a cleaning crop in order to avoid stacking up future problems, which means a no-tolerance approach.


"If you haven’t achieved good control from propyzamide-based products then be brave and mark these areas out, spray them off and re-drill with a hybrid spring oilseed rape," he says.
For those putting problem black-grass areas or fields into spring cropping, Mr Wilcox says minimising soil disturbance at drilling is key to avoiding a flush of black-grass within the spring crop.


Where drill systems disturb more soil, he advises growers to focus on establishing a competitive crop as quickly as possible.
"Delaying drilling until late March or early April when ground is warmer can work, but it isn’t always suitable especially if you’re disturbing more soil as it simply encourages a flush of black-grass at the same time.


"You may be better drilling earlier at a higher seed rate when conditions are cooler and black-grass isn’t growing to ensure the crop is in the ground and ready to go as soon as it warms up."

Spring black-grass control tips

    • Map problem areas now ready for treatment
    • Apply post-ems before the second black-grass leaf has emerged
    • Wait until soil temperatures begin to rise and ensure weeds are actively growing before applying a post-em
    • Consider the wider spectrum of weed control available from post-ems beyond black-grass
    • Do not overlook any areas of poor autumn control
    • Consider spraying-off areas of crops where surviving black-grass populations justify to prevent weeds from setting seed and multiplying further
    • Always check pre-emergence product label restrictions before re-drilling after sprayed-off crops
    • Re-drill areas with spring varieties where possible
    • Minimise soil disturbance when drilling spring crops (5cm depth max)


Source: Hutchinsons

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