Invasive weed Black-grass on its relentless creep north

The worsening headache of invasive black-grass is marching north. Dan Finch, an agronomist with DKB Crop Protection, has seen a marked rise in the weed in north east England, whilst Mark Ballingall of SAC has said the last bastion of Scotland has been breached with increased ingress being seen in the Borders and the Lothians.

Both put the rise down to seed being carried on contractors' vehicles and Mr. Ballingall suggests that climate change could be playing its part in encouraging the weed's foothold and its spread.

"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 period of time growers soon end up with their neighbour’s or a contractor's weed burden," said Dan Finch.

Before black-grass, Mr Finch explained that "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." For this sequence he reckoned on "barely spending more than £50/ha for the season."

But having black-grass in the equation, which he added has been tested positive for 'fop and dim' resistance, adds at least an additional £25/ha to the herbicide spend.

"Where black-grass is present, control strategies have to change. I now recommend delayed drilling wherever possible to encourage a good germination flush that can be sprayed off with glyphosate, drilling a competitive cereal variety and applying a pre-emergence herbicide based on 240g/ha of flufenacet, in the form of either Crystal or Liberator."

There is no doubt that stacking herbicide actives is an important part of controlling black-grass, according to weed scientist Stephen Moss.

"Stacking pre-emergence herbicides is now accepted as an effective way of reducing the pressure on post-emergence herbicides whose performance is steadily declining due 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.

"Although every trial tells a different story, generally speaking, a full rate of a flufenacet based herbicide should be the foundation of any pre-emergence strategy. Trials data show clearly that adding other herbicides, such as chlorotoluron, DFF, flupyrsulfuron, prosulfocarb, pendimethalin or tri-allate, 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."

According to BASF's Stewart Woodhead: "Our trials have shown over the last few years, and especially in this last difficult autumn, that no one active ingredient or product is capable of controlling the ever mounting issue of black-grass control, and that an integrated approach to black-grass control 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 pre- emergence 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."