First case of glyphosate resistance in a UK weed (Italian rye-grass) confirmed

The UK Weed Resistance Action Group (WRAG) has confirmed the first case of resistance to the herbicide glyphosate in a UK weed species.

Resistance at the maximum label rate of glyphosate was identified in tests on a single field population of Italian rye-grass (Lolium multiflorum).

The population was from a site considered to have an elevated risk of developing glyphosate-resistant weeds.

At this site, relatively large Italian rye-grass plants survived appropriately high rates of glyphosate before a relatively late-drilled spring crop.

Since 2019, over 300 weed seed samples have been tested in herbicide resistance screens by ADAS and NIAB.

To date, there has been no indication of glyphosate resistance in any other sample screened, although a small number of other cases are under investigation.

Globally, most cases of glyphosate resistance in Italian rye-grass have been in North and South America.

Although some cases have been reported in Europe (2006 in Spain and 2012 in Italy), identification and management of problematic weed populations mean it has not become a widespread issue.

The presence of glyphosate resistance in the UK emphasises the importance of following the WRAG glyphosate resistance management guidelines, as part of a proactive approach.

A reactive approach is now also required. This year, ADAS will screen Italian rye-grass populations that survive glyphosate applications (prior to drilling a spring crop) to help confirm if resistance is present* (or if poor control is due to something else).

The screens will be conducted on live plant samples submitted by farmers or advisers. ADAS will prioritise the highest-risk samples and report back findings to inform in-field actions (individual test results and locations will be kept confidential).

*Although the rapid tests identify high-risk populations, they do not indicate whether glyphosate resistance is present at a field scale.