Weeds in the UK have developed resistance to herbicides, putting crop productivity and food security at risk, according to a new study.
Researchers conducted a nationwide epidemiological assessment of the factors that are driving the spread of black-grass in the UK. Black-grass is a pervasive weed with increasing resistance to herbicides. The trend could pose a significant threat to cereal crops if new weed control strategies are not adopted, researchers warned.
Published on Monday in the journal Nature Ecology & Evolution, the study was the result of collaborative work led by the University of Sheffield, with the Zoological Society of London and Rothamsted Research.
The team mapped the density of black-grass populations across 70 farms in England and collected seed from 132 fields. They also gathered historical management data for all of the fields to see which management factors were contributing to the increasing prevalence and herbicide resistance of black-grass populations.
“Field monitoring indicated that the level of resistance to herbicides was correlated with population density, indicating that resistance is a major driver for black-grass population expansion in England,” said Paul Neve, a weed biologist and leader of Rothamsted’s strategic programme, Smart Crop Protection.
The study also found that populations resistant to one herbicide were likely to show resistance to multiple classes of herbicides. At Rothamsted, a non-profit research centre that focuses on strategic agricultural science, researchers “used glasshouse bioassays to determine that 80% of sampled populations were highly resistant to all herbicides that can be used for selective black-grass control in a wheat crop,” according to Neve.
Additionally, researchers found a correlation between resistance and the frequency of historical herbicide applications. This suggests that evolution of herbicide resistance in black-grass is primarily driven by intensity of exposure to herbicides, according to the authors.
“We found that the extent of herbicide resistance was primarily dictated by the historical intensity of herbicide use, and that no other management factors had been successful in modifying this resistance risk,” said Neve.
Scientists warned of the considerable economic costs of evolved resistance, which can double the cost of weed control programs. The team surveyed farmers to learn about their use of herbicides and how much different approaches cost them. They found that increased weed densities result in higher herbicide costs and lower crop yields, which leads to significant losses in profits.
As a result, scientists highlighted the importance of managing threats to food production systems using an “evolutionarily informed approach” in a proactive rather than reactive manner.
The team said that mixing different chemicals or applying them cyclically – methods often used in weed control programs – did not prevent resistance from developing. They also cautioned that even when new herbicides are developed, weeds could evolve resistance. Based on these findings, researchers advised farmers to switch to weed management strategies that rely less on chemicals.