Evolved herbicide resistance driven by chemical usage

Scientists from the University of Sheffield have identified factors which are driving the evolution of herbicide resistance in crops – something which could also have an impact on medicine as well as agriculture.

Xenobiotic chemicals, such as herbicides, fungicides, insecticides and antibiotics, are used in both agriculture and healthcare to manage pests and diseases. However, resistance has evolved to all these types of xenobiotics, rendering them ineffective with serious consequences for crop production and health.

Lead author of the study Rob Freckleton, Professor of Population Biology from the University of Sheffield, said: “The driver for this spread is evolved herbicide resistance: we found that weeds in fields with higher densities are more resistant to herbicides. Once resistance has evolved it does not seem to go away: two years later, fields with high densities still had high densities, despite farmers employing a suite of different management techniques.”

In the study, published in Nature Ecology and Evolution, researchers examined the evolution of herbicide resistance in black-grass (Alopecurus myosuroides) in the UK. This has become a widespread weed present in 88 per cent of 24,824 of quadrats – small areas of habitat selected at random as samples for assessing the local distribution of plants and animals – monitored by researchers. It has spread northward in recent years and the scientists found the weed in areas where it had not been found in previous decades.

The research offers important insights into diversifying management which is suggested as a possible technique for reducing the evolution of resistance. The study showed the technique will work to reduce resistance only if farmers reduce their inputs of herbicides. If they continue to use the same levels of herbicides or even increase their input, then this technique will not work.

The study suggests the volume and diversity of herbicide products are positively related to each other. Professor Freckleton said: “The results were simple: farms that used a greater volume of herbicide had more resistance.”

“Beyond this we found little evidence for a role of any other management techniques: neither the diversity of chemicals used – for example whether farmers used a variety of herbicides or just one – or diversity of cropping mattered, despite both being advocated as methods to reduce the evolution of resistance.”