More potential cases of glyphosate resistance in Italian rye-grass

The Weed Resistance Action Group (WRAG) has identified more populations of Italian rye-grass in the UK that may be resistant to the herbicide glyphosate.

At the start of 2025, WRAG confirmed the first three cases of glyphosate resistance in the UK (in Kent, Gloucestershire and North Yorkshire), which were all in Italian rye-grass (Lolium multiflorum) populations.

These populations demonstrated significantly reduced control from appropriate doses of glyphosate. A fourth population (Essex) also showed decreased glyphosate sensitivity.

Following widespread publicity, 10 more samples of Italian rye-grass (populations from eight farms) were identified for rapid screening, where live plant samples were potted up and sprayed with appropriate glyphosate doses by ADAS.

A high risk of resistance was identified at three farms. Population offspring will now be tested to confirm the resistance status.

All resistance cases were from high-risk crop management situations and likely evolved from independent selections (i.e. resistance was not physically spread).

In spring 2026, ADAS will screen more populations in the work funded by Bayer Crop Science.

Read WRAG's August 2025 briefing note for information on:

• How glyphosate resistance is confirmed
• The proactive measures required to minimise glyphosate resistance risks
• The reactive measures needed to monitor for and deal with weeds that survive a glyphosate application