Many growers are seeing their profit going up in smoke from an increasing blackgrass burden, but could a return to controlled stubble burning help turn up the heat on the industry's most pernicious weed? Adam Clarke reports
The familiar violent crackle of burning cereal crop residue fell silent in the English and Welsh countryside after the practice was restricted in 1993.
However, it could return in the not-so-distant future as momentum gathers to bring back a cultural weed control measure that could help to slash blackgrass levels.
The industry faces an uphill battle to successfully lobby for a return to stubble and straw burning, but there is a determined movement building to champion its cause.
A key voice in that movement is Yorkshire grower and co-founder of the Twitter group #Clubhectare Jono Dixon, who farms around 230ha of continuous wheat.
Situated near Sunk Island village, a mile north of the Humber Estuary, Mr Dixon believes there is no other option but to allow a return to targeted and controlled burning.
"A poll of around 90 growers conducted on Twitter showed that 94% of them wanted to see a return to burning.
"It's a very sensitive subject and it's going to be difficult to implement in some areas, but we need a return to give us an improvement in blackgrass control," he says.
Since wide-scale stubble burning ceased, growers have increasingly relied on an ever-depleting portfolio of herbicide chemistry to control grassweeds.
This over-reliance on a narrow range of active ingredients has resulted in widespread herbicide resistance and tougher-to-control blackgrass, which in some fields has made it uneconomic to grow wheat.
On his farm Mr Dixon says he has patches of bad blackgrass that has developed resistance to post-emergence ALS inhibitor herbicides such as Atlantis (iodosulfuron + mesosulfuron).
Alongside his agronomist, he conducted his own stubble-burning trial this autumn on a 0.5ha plot.
Establishment of winter wheat plots using a range of cultivation techniques and herbicide programmes followed the controlled burn to look at its effect on blackgrass populations.
A plot that was left undisturbed after a complete burn resulted in 17,000 blackgrass plants/sq m. An adjoining plot that was lightly power-harrowed following the burn resulted in 22,500 plants/sq m.
In the plot of stubble that was not burned and just cultivated with a Vaderstad Top-Down, blackgrass was slower to emerge, with numbers at 2,500 plants/sq m.
These figures show the massive blackgrass seed-bank Mr Dixon and many other growers are fighting and he believes the ability of burning to break seed dormancy will be more important than seed kill.
"If you can enhance and accelerate the seed chit, it will allow us to manage the problem in a much more effective way ahead of a delayed drilling," says Mr Dixon.
The trials have been carried out professionally and a plot combine will come in at harvest to show any yield differences between the different blackgrass control methods.
Mr Dixon hopes the information gained from his trials will contribute to a case that can be put across to the government for a return to burning.
He envisages a very strict licensing system whereby a farm's blackgrass problem is independently assessed for its need to burn and a cap of around 20% of the land area enforced each season.
"Timing, efficiency and some common sense will be vital if burning returns, and we wouldn't be able to afford any mistakes," says Mr Dixon.
Tough battle
Involved in the original debate with government to keep burning in the late 1980s, NIAB TAG blackgrass expert Jim Orson believes it will be extremely tough to return to full-scale burning.
The original decision to restrict burning was driven by forces outside agriculture, namely air quality and environmental concerns.
Mr Orson says even if there had been the herbicide resistant blackgrass populations that exist now, the outcome may have been the same.
"We presented evidence showing benefits of straw and stubble burning, but it was banned anyway and I'm not sure that view will be changed.
"If it does return, it would be a huge breakthrough in government and public sympathy for agriculture," he explains.
The expert consensus is that a combination of cultural measures such as stale seed-beds, delayed drilling and spring cropping will bring blackgrass under control.
These would still be combined with the most effective herbicide chemistry, but the integrated approach would result in those products being under far less pressure.
"Farmers are trying to control huge populations with herbicides and to be effective they need to achieve a huge percentage of control.
"In many cases they don't stand a chance with chemicals alone," says Mr Orson.
Much research has been carried out on the burning of stubble and its benefits in the arable rotation, with data suggesting that in good conditions up to 70% kill of blackgrass seed can be achieved.
That figure drops to 40% when expressed as an average figure, with damp conditions often preventing the "hot burn" that you need for maximum efficacy.
Mr Orson point out that even with a 70% kill of viable blackgrass seed from an effective burn, the level of control required from chemicals in a continuous wheat established by non-inversion tillage to 20cm depth would still be 90%.
"It could be an important step, but it is certainly not the only answer and there are so many 'ifs and buts'.
"You would be naive to think that just setting a match to the problem will result in everything returning back to normal," adds Mr Orson.
Stubble and straw burning – the rules
*.It is currently illegal to burn chopped cereal straw and stubble and oilseed rape, bean and pea residue - unless for crop protection purposes
*.Linseed residue, broken bales, old straw stacks and animal bedding can still be burned in the field
*.Exemptions are made for experimental and burning training purposes
*.It is still legal to burn cereal straw and stubble in Scotland
Tractor-mounted burners show promise
In addition to controlled burning, technological innovation could also help in the blackgrass battle and trials have been carried out this autumn using tractor-mounted gas burners.
Yorkshire-based company Thermoweed has been providing weed control and desiccation solutions for organic and horticultural clients for more than a decade.
However, in autumn 2013 trials began with some cutting-edge infrared burner technology that will deliver greater control of the burn and more efficient gas use.
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