Autumn weed control messages from TAG

Winter wheat growers must look harder at their intended herbicide programmes, urged research and technical director Jim Orson.

Blackgrass control from Atlantis (iodosulfuron-methyl-sodium + mesosulfuron-methyl) was slipping, isoproturon and trifluralin’s were being withdrawn and there was cross-compliance uncertainty over pendimethalin doses, Mr Orson said.

Indeed if latest EU proposals were adopted, the only grassweed products left would be Topik (clodinafop-propargyl) and Defy (prosulfocarb), he warned.

There were already 132 cases of resistance to Atlantis, the range of alternatives was increasingly limited, and there were no obvious new products in the pipeline.

“There’s no cavalry coming over the horizon,” said Mr Orson.

The other key active ingredient was flufenacet (as in Crystal and Liberator) used pre-emergence.

“If we lose Atlantis we won’t be able to control high populations.

“Are we now at the stage where we have to reduce populations by cultural means? It’s not an easy question, but one that every farmer should ask and debate.

“You have to ask yourself whether it’s really worth using it [Atlantis] to control low populations.” It might be better to restrict its use, and so avoid increasing resistance pressure, to where it was really required – to tackle just a “handful” of plants/sq m, he suggested.

TAG trials applying straight flufenacet (from Italy) pre-emergence showed that nearly all the blackgrass control from Crystal and Liberator came from their flufenacet.

“The more you put on the more control you get.” But there were environmental and crop phytotoxicity constraints, he pointed out.

The pendimethalin in Crystal made it more effective than Liberator when seed-beds were fine and moist. But Mr Orson feared its over-use could encourage resistance, particularly as it was also used in beans. “I believe we should be backing off pendimethalin a little in wheat.”

Whether extra diflufenican might boost Liberator’ blackgrass control was worth exploring.

Defy, a good flufenacet mixer, had been described as the new but costlier trifluralin, he noted.

Avadex (tri-allate) had performed well in TAG trials but needed applying separately.

Pre-em Lexus (flupyrsulfuron-methyl) mixtures offered good blackgrass control in barley. But its use on wheat ruled out Atlantis follow-ups.

That left chlorotoluron as the only other option. “This year, we could not separate it from IPU at full doses,” said Mr Orson. “But we’re concerned that on some winter barley varieties it’s not as safe as the companies suggest.”

‘Risky’ energy-saving experiments underway

Under-canopy clover (an organic growers’ technique to provide crop nitrogen) and strip tillage are among ideas to reduce energy use being explored in TAG’s New Farming Systems long term trials, now in their second year.

The work is charitably-funded by the Morley Agricultural Foundation and the JC Mann Trust, allowing more “risky” work to be undertaken, explained chief executive Colin MacEwan.

Fertiliser and fuel account for about 75% of the energy needed to grow wheat, noted researcher Ron Stobart. “Of that over 50% is down to fertiliser.”

Last season’s winter wheat undersown with clover had yielded 0.75t/ha more than that getting no N fertiliser which gave just 4.5t/ha (1.8t/acre). But more significantly the clover recovered well from pre-harvest Roundup (glyphosate) and also survived pre-sowing discing and subsequent conventional herbicide programme in the next wheat, he explained.

“It shows that once the clover is established we can afford to be quite robust with our weed control.”

The next step, in smaller plot work, was to determine what proportion of the bag N could be replaced by clover’s contribution before the latter was overly suppressed, he explained.

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