The overuse of herbicides could be costing the UK farming economy £400m per year because of resulting resistance to them, including the scourge of black-grass.

Scientists from international conservation charity ZSL (Zoological Society of London) have, for the first time, put an economic figure on the herbicidal resistance of that major agricultural weed that is decimating winter-wheat farms across the UK.

Black-grass is a native annual weed which in large infestations in cropping fields can force farmers to abandon 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.

Heralded as ‘Western Europe’s most economically significant weed’, it is setting back the UK economy by £400m and an estimated 800,000 tonnes of lost wheat yield each year.

Published in 'Nature Sustainability', recently, by researchers from ZSL’s Institute of Zoology, Rothamsted Research and Sheffield University, who have devised a new model which helps quantify the economic costs of the resistant weed and its impact on yield under various farming scenarios.

It said that an estimated 4m tonnes of pesticide are applied to crops worldwide each year, and there are now 253 known herbicide-resistant weeds 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 pesticides are severely lacking.

The research found that the UK is losing 800,000 tonnes in wheat yield each year – equivalent to roughly 5% of the UK’s domestic wheat consumption – due to herbicide resistant black-grass. A worst-case scenario – where all fields contained large amounts of resistant black-grass – is estimated to result in an annual cost of £1bn, with a wheat yield loss of 3.4m tonnes per year.

Lead author from 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.”

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, giving resistance to chemicals the plants have never even been exposed to.

Under-fire herbicide, glyphosate, remains one of the few herbicides that black-grass has not evolved resistance to, though evidence from a recent study shows that resistance to it 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.

“Understanding the economic and potential food security issues is a vital step, before looking at biodiversity, carbon emissions and water quality impacts in greater detail.”