Research by Rothamsted has helped put an economic figure on herbicide resistance in blackgrass, the farmland weed that is decimating winter-wheat yields across the UK.

Heralded as ‘Western Europe’s most economically significant weed’, herbicide resistant blackgrass is costing the UK economy nearly £400 million and 800,000 tonnes of lost harvest each year, with potential implications for national food security.

Published in Nature Sustainability, the study presents a new model which helps quantify the economic costs of the resistant weed and its impact on yield under various farming scenarios.

The worst-case scenario – where all fields have a high proportion of resistant black-grass – could result in an annual cost of £1 billion, with a wheat yield loss of 3.4 million tonnes per year.

The modelling was carried out by international conservation charity ZSL (Zoological Society of London) based on resistance assay research that was carried out by Rothamsted.

The simulation estimates the UK is currently losing 0.82 million tonnes in wheat yield each year (equivalent to roughly 5% of the UK’s domestic wheat consumption) due to herbicide resistant black-grass. This comes at a cost of £380 million per annum.

Infographic showing the cost of herbicide resistant black-grass in the UK

Black-grass is a native, annual weed and large infestations in farmers’ fields can force them to abandon their winter wheat – the UK’s main cereal crop.

Farmers have been using herbicides to try and tackle the black-grass problem – but in many areas of England the agricultural weed is now resistant to these herbicides.

An estimated four million tonnes of pesticide are applied to crops worldwide each year. There are 253 known herbicide-resistant weeds already, and unlike the known-costs to the economy of human antibiotic resistance – which runs into trillions of dollars – estimates of the costs of resistance to agricultural xenobiotics (e.g. antimycotics, pesticides) are severely lacking.

Over-use of herbicides can lead to poor water quality and causes loss of wild plant diversity and indirect damage to surrounding invertebrate, bird and mammal biodiversity relying on the plants.

As wheat is the main component of many household basics like bread and pasta, consumers may end up absorbing any increases in cost, and so the issue of black-grass should be considered as a nation-wide issue affecting both people and wildlife.

Lead author and postdoctoral researcher at ZSL’s Institute of Zoology, Dr Alexa Varah said: “This study represents the first national-scale estimate of the economic costs and yield losses due to herbicide resistance, and the figure is shockingly higher than I think most would imagine.

“We need to reduce pesticide use nationwide, which might mean introducing statutory limits on pesticide use, or support to farmers to encourage reduced use and adoption of alternative management strategies. Allocating public money for independent farm advisory services and research and development could help too.”

Management industry recommendations have so far advised using a mixture of herbicides, designed to prevent the evolution of ‘specialist’ resistance, however alarmingly recent research has revealed that this method actually alters the type of resistance to a more generalist resistance – and in some cases gives resistance to chemicals the plants have never been exposed to.

Glyphosate is now one of the few herbicides that black-grass has not evolved resistance to, with farmers now reliant on repeated applications to control the weed. However, evidence from a recent Rothamsted study shows that resistance to glyphosate is now evolving in the field too.

Dr Varah added; “Farmers need to be able to adapt their management to implement more truly integrated pest management strategies – such as much more diverse crop rotations and strict field hygiene measures.

“Currently resistance management is the responsibility of individual practitioners, but this isn’t a sustainable approach. It should be regulated through a national approach, linking the economic, agricultural, environmental and health aspects of this issue in a National Action Plan – that also targets glyphosate resistance.”