Italian ryegrass is a common weed in cultivated crops
John Cussans
Weeds resistant to the herbicide glyphosate have been discovered in the UK for the first time. The species in question, called Italian ryegrass, is widespread in the UK, but grains impervious to the chemical have only been found on one farm in Kent.
Glyphosate is helping farmers adopt greener farming practices known as regenerative agriculture, he says John CussansWeed management expert from ADAS consulting firm. His team confirmed that the plants were resistant in tests in a greenhouse.
“It could affect our ability to transition our farming system,” says Cussans. “Herbicide resistance to glyphosate is a very significant practical problem on a farm.”
In the UK, farmers use glyphosate mainly to clear all the plants in a field before planting the seeds. This allows them to avoid plowing, which damages soil health, increases erosion and reduces carbon storage.
Minimizing soil disturbance is one of the key focuses of regenerative agriculture, along with crop rotation and soil cover maintenance.
“Glyphosate is quite beneficial compared to other agrochemicals,” he says Helen Metcalfe Rothamsted Research in Harpenden, UK. “It shows very low bioaccumulation and low toxicity. And it supports regenerative practices like no-till, which is great for soil health. In fact, it can have environmental benefits compared to some alternatives.’
Weeds are a big problem for farmers, he says Paul Neve at the University of Copenhagen, Denmark. “We lose more crop yield to weeds than to insect pests and pathogens.”
Worldwide, at least 56 grass species, including Italian ryegrass (A multi-flowered lily) have developed glyphosate resistance, which has occurred independently in hundreds of different locations. Such weeds are a major problem for many farmers in the US and Argentina, where crops developed to be resistant to glyphosate have been grown on a large scale for many years.
“But actually, given that the first case was 30 years ago, this hasn’t exploded into a big problem,” says Neve.
Resistant weeds are a big problem on farms, says Neve, but weeds spread more slowly than, say, insecticide-resistant insect pests. Taking precautions such as cleaning farm equipment to remove seeds can slow the spread.
Farmers also need to take a variety of weed control measures and not just rely on glyphosate, says Metcalf. “If farmers control weeds and implement all these alternatives to glyphosate, we’ve seen that it’s possible to start making a profit within five to 10 years,” he says.
Cussansen’s team stepped up surveillance in the UK in 2018, testing more than 300 samples of Italian ryegrass. He believes that the resistant plants on the farm in Kent evolved in situ, rather than being brought in from elsewhere.
He also believes that resistance has taken much longer to evolve in the UK than in other countries, because farmers there do not grow genetically modified crops or grow them conventionally to be resistant to glyphosate. With such crops, glyphosate can be applied to control weeds while the crops are growing and before seed is planted.
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