Life without two familiar herbicides was the main theme of the second of this year’s Farmers Weekly Arable Club meetings. Andrew Blake reports

Weed control will become more expensive for many cereal growers next autumn and increasingly difficult in barley and oats.

That became clear at last week’s Bayer CropScience-sponsored meeting of FW Barometer farmers, Farmer Focus writers, other farmers and agronomists.

Highlighting the challenge posed by the impending withdrawal of isoproturon (IPU) and trifluralin, Bayer’s Tim Holt estimated that they accounted for nearly half the 5m hectares of cereals treated with autumn herbicides.

About 2m hectares (5m acres) received IPU last season, figures suggested. “It’s been the mainstay of all sorts of programmes,” said Mr Holt.

Trifluralin accounted for a further 0.5m hectares (1.2m acres). But sales of both would be banned beyond September.

“We have 2.5m sprayed hectares to replace within a year – that’s the challenge.”

In theory it would not be until autumn 2009 that growers definitely needed to cope without either herbicide. But how much of each remained available next autumn was unclear. And after last season’s generally good spraying conditions and extra sowings under zero set-aside Mr Holt suspected many growers would need to seek alternatives.

“We think there’s probably less than 50% of the normal amount of IPU left on farms and in distributors’ stores.”

Over half the IPU used was aimed at annual meadowgrass, and its demise meant growers would lose spraying flexibility, warned Mr Holt.

“IPU has been popular because it can go on any time from pre-emergence up to GS32, it mixes well with other products and always gives some sort of a result.”

There were plenty of meadowgrass-controlling alternatives from the Bayer stable (see panel) and elsewhere. But growers needed to decide whether to concentrate on spraying mainly residual products early or to leave control until later with mainly contact-acting materials, he said.

“A lot of them control meadowgrass and broadleaved weeds pre-em or peri-em, but if you leave it too late they won’t work.”

Likewise the early to late post-emergence options did not work pre-em.

The cost of control was bound to rise, delegates accepted. Andrew Blenkiron, Wolverhampton Barometer farmer, estimated that using Graduate was about £5/ha (£2/ha) more expensive than relying on IPU.

He had also successfully tried Othello, test-marketed for the first time in last year’s open autumn. But he said he would not want to rely on post-emergence products in case application was delayed in trickier seasons when the priority was to finish drilling.

“It went on quite late and took a lot of pressure out of the system.”

Hereford AICC member David Lines, who felt his clients might be prepared to spend a bit more in the light of increased grain prices, expected to see more chlorotoluron applied in wheat. “90% of varieties are tolerant,” he noted.

A pre-emergence mix with Defy (prosulfocarb) it had done a “cracking job, though you have to watch the overlaps.”

But chlorotoluron was also increasingly under scrutiny, he noted. “It’s not quite as soluble as IPU, but it costs just as much to take out of water. I would guess that it’s only two or three years before it goes.”

He was also concerned that the relatively low concentration of mesosulfuron in Othello might encourage blackgrass resistance. But Bayer’s Gilles Chevalier stressed that it was not recommended if blackgrass was present. “In that case you should go for Atlantis or Pacifica.”

Whatever the approach the earlier that meadowgrass was tackled the cheaper it was likely to be, Mr Holt pointed out.

“The residuals are definitely cheaper than the post-ems. Liberator at 0.3litres/ha is most cost-effective, but it needs a good seed-bed.” If conditions dictated resorting to 1 litre/ha of Othello growers would inevitably spend more. The longer you leave it the more it’s going to cost.”

Barley and oats weed control

With IPU gone, barley growing would become impossible on his blackgrass-infested land, said Gloucester former Farmer Focus writer Richard Ward. “We can’t use Atlantis on barley.

“We tend to use quite a bit of Avadex because seed growers we don’t want wild oats.” It helped against blackgrass, but was insufficient by itself, he said.

Avadex (tri-allate) had “rather slipped off the radar screen”, but remained an option, acknowledged Mr Holt.

Mr Lines wanted to know what might replace trifluralin on oats. “The oats herbicide market is woefully short.”

Mr Holt responded that he believed approval for Bacara was being sought

Bayer meadowgrass herbicides

Residual

Bacara and Graduate (flurtamone + diflufenican)

Firebird and Liberator (flufenacet + diflufenican)

Contact

Atlantis & Pacifica (mesosulfuron + iodosulfuran)

Hussar (iodosulfuron)

Othello (mesosulfuron + iodosulfuron + diflefenican)