Fears of rising herbicide resistance in blackgrass have triggered a call for a return to straw and stubble burning to help boost control of the weed and prevent the problem from spreading.
An online debate took off after Lincolnshire grower Mark Pettitt said he wanted to see controlled straw burning reintroduced to allow him to control the 40% of blackgrass on his farm that was resistant to Atlantis (iodosulfuron + mesosulfuron).
“If I could burn just 10% of my wheat acres each year, that would clean up my bad blackgrass patches,” he wrote on Twitter. “I used to min-till when we burnt everything, now I have to plough the lot. And in bad blackgrass areas in year two, you plough viable seeds back up.”
Reaseheath College agronomy lecturer Mark Sheridan also took part in the Twitter debate. He believes straw burning could be used alongside other cultural control measures to help combat the blackgrass threat, especially as key herbicides such as trifluralin and isoproturon have gone and others are under increasing legislative pressure.
“We shouldn’t forget other cultural controls that should be employed in the fight, but burning would be another piece in the armoury,” he says. “It used to be considered good arable husbandry.”
Most people tweeting on the issue had agreed, and the speed at which the debate snowballed demonstrates the need to reopen the debate on a much wider scale, he adds.
“I’m sure farmers would stick to the guidelines – we could have licenses or management plans in place and farmers have a good track record in this area, for example with NVZs and the Voluntary Initiative.”
He believes a return to controlled burning could become more necessary if anecdotal reports of glyphosate resistance in blackgrass in eastern England materialise.
“We know resistance is spreading in the USA, where it is widely used on genetically modified crops. If we lose glyphosate, we are on the edge of a precipice.”
Another contributor to the debate, Yorkshire grower Richard Morrell, says blackgrass is not a huge problem on his 200ha of arable at Towthorpe Manor Farm near Driffield – and he wants to keep it that way.
“If I could burn patches to stop it spreading over the rest of the farm and really getting hold that would be a good thing. Surely burning 10 or 20 acres now rather than having to spray the whole farm with Atlantis has to be better for the environment.” Controlled burns could be approved by BASIS-qualified agronomists, he adds.
Increasing reliance on GM in other countries means less investment in new herbicide chemistry, he points out. “If we are not going to have GM then we will need some other way. It would be well worth doing some more burning trials work to demonstrate the benefits.”
Stephen Moss, weed scientist at Rothamsted Research, says trials carried out in the early 1980s show burning could provide valuable control of grassweeds.
“Direct kill of seeds was typically 50% and often as high as 70%,” he says. “It also broke dormancy on some of the remaining seeds so you got an earlier flush and could use min-till.”
However, the work showed the resulting ash layer could impede pre-em herbicide efficacy where shallow cultivations were employed, he adds.
A return to burning is “highly unlikely”, says Dr Moss. He suggests growers should kill off bad areas of blackgrass with glyphosate soon after the weed’s ears have emerged in early June. That will reduce the seed burden by 70-80% each year, leaving only about 3% viable by year three.
“You don’t need a state-of-the-art GPS – just a few notes and a bit of forethought is all that’s required.”