Loss of IPU and trifluralin will make grassweed control harder in barley as well as wheat

It’s not just pre-emergence grassweed control in winter wheat which will be more difficult once IPU and trifluralin have gone, Syngenta weed control experts said at a Cambridge seminar last week.

Growers would also have to re-think their barley weed control programmes, as well as going back to the drawing board to get good control of annual meadowgrass.

Around 2m hectares of cereals have been treated with IPU and trifluralin annually, leaving a big void to be filled.

“Trifluralin has had an important role at the pre-emergence timing in wheat, both in cheapening mixes and as an anti-resistance option,” said Jason Tatnell.

In contrast, IPU’s role in wheat had been at the early post emergence timing, as a holding spray, he added. “We’re losing the holding spray option now – growers must be prepared for the impact of that.”

IPU had also been a mainstay for blackgrass control in winter barley, as well as the most widely used product for annual meadowgrass control, he said.

“The implications for blackgrass control are that there will be even greater reliance on Atlantis and the pre-emergence timing will be more critical than ever.”


Growers would have to guard against an over-reliance on pendimethalin and make greater use of cultural control methods, he advised. “They will need to find a new approach for annual meadowgrass and broadleaved weeds, as well as changing their policy in winter barley.”

Where annual meadowgrass was the main target, Chris Rowsell suggested a mixture of Defy + DFF would be a cost-effective, standard solution.

“It’s a catch-all recommendation,” he said. “Pre-emergence use is the strongest option, but it can be applied up to the three-leaf stage of the annual meadowgrass.”

Alternatives include the use of Defy with PicoPro, pendimethalin, chlorotoluron or flurtamone/DFF. “These all have different strengths and weaknesses, depending on the other weeds present.”

Using Defy with DFF would give similar control levels to those achieved with IPU, he concluded.

Mr Rowsell said that new pre-emergence standards for blackgrass control were now needed. “Atlantis on its own is not enough, especially where you have high populations of blackgrass. So the pre-emergence treatments are vital, especially if we want to protect Atlantis for the future.”

Putting DFF with Defy at pre-emergence had raised the levels of blackgrass control to 93%, some 10% more than when trifluralin was the partner product, he said. “The DFF component makes a significant contribution to blackgrass control – it’s been very apparent in trials this year.

“Where Liberator is used, control has been even better at 96%. So that’s the best option for difficult situations, but it does cost more.”

Pendimethalin as a partner for Defy had been less effective on blackgrass. “But it’s still a good mixture for ryegrass.”

Syngenta was supporting six Defy mixes each for wheat and barley this autumn, confirmed Mr Rowsell. “It’s important to note that although Defy mixes show a greater margin of safety over current standards, the seed should be covered with 3cm of settled soil.”

Winter barley

Without IPU and trifluralin, the remaining post-emergence options weren’t strong enough to get good blackgrass control in winter barley, warned Mr Rowsell.

“A greater emphasis on pre-emergence treatments will be required,” he said. “Growers will also need to put more focus on cultural control methods.”

Again, higher standards of pre-emergence control were needed. “A good option for winter barley is to use Defy with Lexus pre-emergence, followed by a post-emergence spray of Axial with pendimethalin very soon afterwards.”

Defy with DFF is another good pre-emergence option, he suggested. “All of our supported winter barley Defy mixes should be applied pre-emergence.”


  • Defy – prosulfocarb
  • Atlantis – mesosulfuron-methyl + iodosulfuron-methyl
  • Hurricane – diflufenican
  • Lexus – flupyrsulfuron-methyl
  • PicoPro – pendimethalin + picolinafen
  • Liberator – flufenacet + diflufenican
  • Axial – pinoxaden
  • Crystal – flufenacet + pendimethalin

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