Atlantis applications to control blackgrass in wheat are more likely to be after Christmas than before, according to leading agronomists.
Later drilling, effective pre- or peri-emergence applications and an earlier slowing of growth as temperatures cool have combined to make blackgrass plants unlikely to reach the two to three-leaf optimum growth stage for Atlantis (mesosulfuron-methyl + iodosulfuron-methly-sodium) applications, said Peter Riley of Prime Agriculture at a Bayer CropScience-organised round-table discussion.
“We are already revising the amount of Atlantis we are going to use this autumn,” he said. “At the start of the season we were aiming to do 30-40% in the autumn. Now it will probably be 10-20% autumn, maybe even less than that.”
Autumn applications of Atlantis were most likely in earlier-drilled crops that did not, for some reason, receive a pre- or peri-emergence application, he suggested.
Most crops won’t be forward enough this side of Christmas for Atlantis applications, agronomists suggest.
But crops drilled in the past two or three weeks were unlikely to reach the three-leaf stage, while earlier drilled crops that received a robust pre- or peri-emergence treatment would also struggle to be ready for Atlantis applications before it became too cold, he said.
Emergence had slowed too, said David Ellerton of ProCam. “There was definitely a flush of blackgrass early on, but we’re not seeing much coming through now.”
That was confirmed by ADAS’s Sarah Cook, who has been monitoring emergence of blackgrass with known dormancy levels in large tub experiments. About 25% had emerged this season, which was more than the equivalent period last season, but germination was beginning to plateau, she said.
The question now was whether there would be a further flush. Last season there was no significant spring flush, Dr Cook noted.
But poorer, cloddy seed-beds this season could complicate the issue, said Gary Jobling of Bayer CropScience. “Will we see a further flush when clods break down?” he asked.
That made it important to get a base residual herbicide coat on now, if it hadn’t already been applied. “The base coat will reduce the amount coming through,” he added.
Mr Riley agreed that if small blackgrass was just coming through, it was worth doing something now. He suggested a flufenacet-based residual plus either IPU or chlorotoluron if blackgrass had emerged, or just the flufenacet product if the weeds were still pre-emergence.
That, along with the option of using Defy (prosulfocarb) instead of flufenacet, was also Dr Ellerton’s recommendation.
He was keen for growers to make full use of alternative modes of action to help keep Atlantis resistance at bay, and pointed out that in some cases, where blackgrass was “easier”, follow-up sprays might not be needed, or only on small patches.
Using IPU or CTU also meant a six-week interval was needed before Atlantis could be applied because of potential antagonism, said Mr Jobling. “If you’ve got a high population and knock 1-3% off control, you will see it.”
Atlantis needed vibrant, healthy blackgrass plants for it to work effectively, said Mr Riley. “If you’ve got that, it will kill them. If you haven’t, it might not.”
Application was also crucial to good efficacy, said Mr Jobling. “Forward speed is important. Don’t go whipping across too fast – it compromises good coverage.”
How much residual herbicide had already been sprayed depended on location, said Dr Ellerton. In East Anglia, the south-east and the Midlands, the vast majority of cereals had been drilled and quite a lot of pre-emergence had been applied.
In the south-west, the drilling picture had improved in the past 10 days, but little pre-emergence had been applied. “Most will get a post-emergence as soon as possible,” he added.
Growers had been concentrating on drilling in the north, so little pre-emergence spraying had been done there, he said. “In the north-west it is desperate – very little has gone into the ground there.”