A new publicly-funded research project is seeking chinks in the black-grass armour which may reduce the impact and extent of herbicide resistance. Andrew Blake reports.
Understanding how black-grass becomes resistant to previously highly effective herbicides is the key aim of a £2.64 million, four-year research project which got under way in May 2014.
Black-grass resistance has reached epidemic proportions in England, affecting 1.2m hectares, says one of the project’s leading scientists Paul Neve, of Rothamsted Research.
“It’s responsible for major yield losses in wheat, and it’s now one of the major constraints to sustainable arable production systems and driving management changes in arable rotations,” says Dr Neve.
“The degree of resistance to Atlantis, the main herbicide being used for chemical control of black-grass has been alarming.
“But there’s a lack of understanding of how plants evolve resistance, and we hope the insight generated by the project will lead to novel management options, diagnostic tools and decision-support aids.”
The idea is by sampling and determining the genetic basis of specific black-grass populations growers may be able to employ ‘more targeted weed therapy management’.
The research integrates basic molecular biology to understand how plants become resistant, evolutionary biology to determine how resistance spreads through populations, and ecology and agronomy to explore the impacts of resistance on farming systems.
“Using modelling approaches, we’ll explore the effectiveness of various management strategies to slow the evolution of resistance and design novel management strategies with less reliance on herbicides.
“Towards the end of the project, further analyses will examine the impacts of changing management on economic and environmental indicators at the whole farm and landscape level.”
The first year of the project has involved an unprecedented national resistance audit by teams at Rothamsted and the University of Sheffield, says Dr Neve.
“Detailed, in-field black-grass population surveys were conducted on 132 fields across England to derive field maps of infestation.”
“At each site, black-grass seed was collected and populations tested for resistance to key herbicides. Field management histories have also been collected for all the farms involved.
“In time, we hope to combine these data sets to explore the impacts of black-grass and herbicide resistance on farm management and to determine which practices are associated with modifying the risks of evolution of herbicide resistance.”
*AHDB Research project 2012-3807
“The scale of the problem will be no great surprise to many, though the degree of resistance found is alarming,” says Dr Neve.
However, researchers at Newcastle University have already pinpointed several biomarkers with links to genes apparently helping black-grass to break down herbicides.
“Molecular diagnostics are common tools in health care, for example in diagnosing cancer,” he says. “Just as a doctor takes a sample from a patient to check whether a tumour is cancerous, growers might be able take a sample of black-grass to diagnose herbicide resistance.
“A negative result – the absence of multiple herbicide resistance – would then lead to an informed decision about which herbicide to apply.
“But what if the diagnostic shows a positive result – i.e. the presence of multiple herbicide resistance? This is the second focus of our research – exploring the potential to counteract the mechanisms which black-grass uses to resist herbicides.
“Firstly, we need to understand what these mechanisms are. In previous research, we characterised several enzymes produced by resistant black-grass which degrade or detoxify the active ingredients in herbicides.
“Collectively, we call these enzymes the plant xenome, which kicks into action as soon as black-grass has taken up the herbicide.
“Surprisingly, plant xenome enzymes are similar to the enzymes which cancer cells produce to detoxify anti-cancer drugs, causing multiple drug resistance [MDR].
“In a recent study, we discovered treating resistant black-grass with an experimental drug for cancer therapy to combat MDR can also inhibit the plant xenome and restore herbicide control.
“Sadly, that drug poses considerable environmental risk and so cannot be developed further as a herbicide synergist. However, this work shows black-grass resistance may have an Achilles heel to be targeted with other therapeutics.
“Novel molecular diagnostics and herbicide synergists which reverse resistance may provide promising breakthroughs for the future; but for now the answer to resistance is judicious use of herbicides combined with cultural weed control options to prolong the life of remaining herbicide options.”
David Brightman and his family have farmed heavy clay soil in Warwickshire for 50 years.
He says: “I can’t remember a time when black-grass wasn’t a problem. However, the dry autumn of 2011 and the wet 2012 raised the problem to a new level.”
Growing spring crops is always risky on Mr Brightman’s land at Gaydon, but to try to tackle it he has decided half the 224ha farm will need to be in spring crops for the foreseeable future and that drilling winter wheat may have to be delayed into October, always a risk on heavy land.
“We’ve worked with black-grass specialist Dr Stephen Moss, of Rothamsted Research, and many commercial companies, but with no new chemistry on the horizon we’re already looking for the next option for black-grass control.
“So we’re really pleased the Black-grass Resistance Initiative consortium has taken up the challenge, and particularly basic, strategic and applied researchers are working together to gain better understanding of the problem as well as techniques to be used in practice.
“Mapping and resistance testing are already proving useful in manipulating seed rates and modifying herbicide use, but we’re really looking forward to new management options, diagnostics and decision support tools.
“If the team manages to find a way of improving the activity of current herbicides it would be a bonus which may be applicable elsewhere.”