A high risk of glyphosate resistance has been found on three more farms – prompting warnings for growers to monitor weeds that survive spray applications.
Italian ryegrass samples from the three latest farms were potted up and sprayed with glyphosate by ADAS. A high risk of resistance was identified. Population offspring are now being tested to confirm resistance status.
It comes after the UK’s first three cases of glyphosate resistance were identified earlier this year. All three cases – in Kent, Gloucestershire and North Yorkshire – were in Italian ryegrass populations.
Findings
The Weed Resistance Action Group (WRAG) said these populations demonstrated significantly reduced control from appropriate doses of glyphosate. A fourth population in Essex showed decreased sensitivity.
After widespread publicity, 10 more samples of Italian ryegrass from eight further farms were identified for rapid screening – typically from situations where plants had survived earlier glyphosate treatment.
A high level of resistance was identified in samples from three of these farms. The resistance cases were from high-risk crop management situations – including where they had been no cultivation and/or very little soil disturbance.
WRAG said there were many reasons for poor control – and thorough investigation was essential to confirm causes. Vigilance and appropriate action could minimise the development of resistance in the field, it added.
Weed control
The situation is particularly concerning because there is no readily available alternative spray to glyphosate – and the agrochemical is the bedrock of weed control in regenerative and other zero tillage farming systems.
ADAS weed control expert John Cussans said growers employing low cultivation techniques should consider what else they could be doing to reduce reliance on glyphosate when faced with a resistance risk situation.
WRAG said all farmers and agronomists should remain vigilant. Growers should familiarise themselves with guidelines for minimising the risk of resistance spreading – including blowing down combines and other equipment.
“The independent nature of populations developing highlights the importance of on-farm hygiene,” it said, adding that Italian ryegrass seeds were often present alongside the ripe crop heads at harvest.
“To prevent spread, thoroughly clean combines and other equipment such as balers or cultivation machinery – and when possible keep all straw within the field – and definitely on farm,” said WRAG.
Further research
Bayer Crop Science, which manufactures the glyphosate-based herbicide Roundup, is funding ADAS to conduct a further year of focused testing to monitor the situation and evaluate any potential resistance.
Italian ryegrass populations will be screened next spring – assessing plants which survived glyphosate applications prior to drilling a spring crop – a high-risk situation.