A glyphosate-resistant population of Italian ryegrass has been confirmed on a farm in Kent, reports the Weed Resistance Action Group (WRAG).
WRAG made the announcement today while stressing that it’s the first field population of any weed to have glyphosate resistance in the UK.
“Glyphosate is probably the most important herbicide for UK farmers and there’s no obvious replacement, hence any case of resistance is concerning,” says ADAS’ John Cussans, who led the research into the case.
“But we must retain perspective – it’s resistance in one weed species on one farm and not a widespread problem yet. For context, during 2018-2023 we’ve collated data for samples of Italian ryegrass which were submitted for standard resistance tests.
“They’ve been screened with glyphosate and we’ve not found a single resistant sample. This single case does however serve as a firm reminder of the importance of glyphosate stewardship, otherwise we’re likely to see more cases,” explains John.
Further concern
At present, in addition to the one confirmed case, three suspect populations of Italian ryegrass are under investigation with results expected later this year. To date, Italian ryegrass is the only weed with suspect populations in the UK; extensive testing of blackgrass and a 2023 survey of 166 brome samples found no populations of concern.
“Experience from around the world suggests ryegrass species are high-risk with regard to glyphosate resistance. Globally, there are several cases of resistance in annual ryegrass Lolium rigidum and Italian ryegrass Lolium multiflorum.
“However, other weeds can also develop resistance. We know that herbicide resistance tends to develop field-by-field so farmers can work to maintain glyphosate efficacy on their farm.”
John stresses the importance of adhering to stewardship guidance, as issued by WRAG – Guidelines for minimising the risk of glyphosate resistance in the UK.
Dealing with suspect cases
He adds that early intervention is vital to minimise the risk of development of more cases of resistance and farmers are recommended to work with a BASIS-qualified advisor to investigate any instances of poor control from glyphosate.
“The vast majority of cases of sub-optimal control with glyphosate will have nothing to do with resistance, it’ll be due to the application rate, timing or conditions. Spring 2024 is a good case in point, many farmers suffered from poor control for one or more of these reasons.
“If you’ve ruled out the obvious causes then seek further advice and consider a resistance test,” he concludes.
CPM will be investigating this story further in its upcoming February issue.
