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Time to Make Tough Calls on Black-Grass

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Spraying off areas of crops affected by black-grass is a difficult call to make, but it is one that more growers are considering in the fight against this increasing problem.

Midlands-based Hutchinsons-Cropwise agronomist Andrew Wright says concerns about 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 approach.

Andrew Wright

Assessing crops during January and February for black-grass that has survived autumn treatments is key to making an early decision that minimises the financial impact and allows more time to sow an alternative spring crop if required, he says.

“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.

“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.”

Where a spring herbicide is to be applied, Mr Wright favours products based on iodosulfuron-methyl-sodium and mesosulfuron-methyl.

He acknowledges efficacy can be reduced where resistance is present, but correct application still delivers worthwhile control of black-grass and other key weed species, such as wild oats and brome.

Spring crops account for 20-25% of the cropping in Mr Wright’s region and he urges anyone going down this route to follow a few simple steps to minimise the risk of stimulating a troublesome black-grass flush within the crop:

•    Prepare seedbeds in the preceding autumn
•    Spray-off with glyphosate in the spring once soil has warmed and black-grass has emerged – typically two weeks before drilling
•    Avoid further soil disturbance before drilling
•    Drill later in spring when soil is warm and crops can establish quickly
•    Minimise soil disturbance at drilling – direct drill if possible
•    Sow competitive crops at a high seed rate to outcompete black-grass e.g. spring barley, up to 400 seeds/m2.

Mr Wright also says the importance of delayed autumn drilling combined with an effective pre-emergence strategy for effectively reducing black-grass numbers before winter has been clearly highlighted this season.

“We’ve seen some excellent results where growers have drilled later – typically after mid-October up to the first week of November – into good seedbeds and have used an effective pre-emergence herbicide strategy that included tri-allate.

“However, where crops have been drilled earlier than this and/or seedbeds have been more cloddy, you can find black-grass coming through in places.”

Spring black-grass control tips

•    Map problem areas now ready for treatment
•    Apply post-ems early when weeds are small, but…
•    Ensure weeds are actively growing
•    Consider the wider spectrum of weed control available from post-ems beyond black-grass
•    Don’t 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
•    Re-drill areas with spring varieties where possible
•    Minimise soil disturbance when drilling spring crops (5cm depth max).