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Black grass: ‘Change of strategies needed’
BLACK grass is marching north with significant increases in the North-East and even cases in Scotland.
Dan Finch, an agronomist with DKB Crop Protection of Walworth, near Darlington, has seen a marked rise in the region while Mark Ballingall, of SAC, said the last bastion of Scotland had been breached with cases in the Borders and Lothians.
Both put the rise down to seed carried on contractors’ vehicles, and Mr Ballingall believes climate change could also be encouraging the weed to spread.
Mr Finch said: “Black grass has been increasing over several years as more farmers opt to use a contractor for combining and baling.
We are seeing that, within a short time, growers soon end up with their neighbour’s or a contractor’s weed burden.”
Before black grass, weed control programmes would work around taking out annual meadow grass (AMG) early with residual Pico Pro (pendimethalin + picolinafen) followed by Axial for rye grass and wild oat control. Mr Finch reckoned that sequence barely cost more than £50/ha for the season, but black grass adds at least an extra £25/ha on the herbicide spend.
He believes black grass control strategies have to change. “I recommend delayed drilling wherever possible to encourage a good germination flush that can be sprayed off with glyphosate, the drilling of a competitive cereal variety and applying a pre-emergence herbicide based on 240g/ha of flufenacet, in the form of either Crystal or Liberator.”
Weed scientist Stephen Moss said stacking preemergence herbicides was now accepted as an effective way of reducing the pressure on post-emergence herbicides whose performance was steadily declining owing to resistance.
“All pre-emergence herbicides are affected by resistance to some degree, but resistance tends to be partial and does not build up rapidly,” he said. “Generally speaking, a full rate of a flufenacet based herbicide should be the foundation of any pre-emergence strategy.
“Trials clearly show that adding other herbicides, such as chlorotoluron, DFF, flupyrsulfuron, prosulfocarb, pendimethalin or triallate, generally increases overall performance. However, stacking ever more herbicides may become unsustainable for reasons of excessive crop damage, cost, legality, water pollution, antagonism and increasing resistance.
“Using a mix of herbicides with different modes of action is likely to slow up selection for resistance.”
Stewart Woodhead, of BASF, said: “Our trials have shown over the past few years that no one active ingredient or product is capable of dealing with the evermounting issue of black grass control, and that an integrated approach is vital.
“We have stacked low resistance risk residual chemistry as part of a programme approach to black grass control.
This has been based around Crystal with the addition of diflufenican preemergence or peri-emergence of the crop either on its own or part of a sequence.
“The sequence will be an SU product with additional residual chemistry such as Stomp Aqua, Auxiliary or Picona applied at 1-2 leaves of the black grass. These help to improve consistency of control.”