Practical glyphosate application guidelines,  by the Weed Resistance Action Group (WRAG), will help arable growers reduce the increasing risk of glyphosate resistance developing in grass weeds. The guidelines have been updated in 2021 following five years of ADAS research into optimising the effectiveness of glyphosate on arable weeds to help prevent resistance.

The impending problem of glyphosate resistance

After 40 years on the commercial market, glyphosate is one of the most frequently used herbicides in UK crop production. Much to the relief of growers, there are currently no known cases of glyphosate resistance occurring in weeds. However, glyphosate’s dependability may soon be in doubt. Evidence has started to emerge that certain grass weed populations, such as sterile brome, are becoming more tolerant to the effects of glyphosate. Concern is spreading that glyphosate resistance will eventually occur, and this stalwart active will no longer provide effective control over common grass weeds. A resistance that, once evolved, is here to stay.

The lack of alternatives

Right now, there are not many actives out there which can do the work of glyphosate. Regulatory policy changes, limited crop rotations, combined with a lack of new herbicide development means a competing alternative any time soon is highly unlikely. The unique role of glyphosate and its place as the standard ‘go-to’, fix-all solution has led to an over-reliance. This, combined with repeated use and incorrect rate for the target weed, are the biggest contributors to the deepening weed resistance risk.

Minimising the risk of resistance

The Weed Resistance Action Group

As with all weed control strategies, the key concern now is to keep glyphosate within the grower’s toolbox for as long as possible by highlighting how and when it should be used. Experts from the research and advice community, Crop Protection Association, agrochemical industry and public sector came together to form the Weed Resistance Action Group (WRAG). Their aim is to independently investigate and coordinate research and communicate its findings, recently to reduce agricultural over-dependence on glyphosate.

WRAG published the initial Glyphosate resistance guidelines in 2015 based on the best expert knowledge at the time were published. These guidelines revolved around four key actions to prevent glyphosate resistance:

WRAG 4 actions

New 2021 glyphosate guidelines

After the publication of the initial 2015 guidelines, AHDB and industry funded research began to quantify exactly how and when glyphosate should be used for maximum effectiveness. In September 2020, work finished on the five-year study to investigate timing and application precision. Multiple experiments took place over the course of the five years, both in container and in field. Varying glyphosate rates and timings were administered across two of the most common arable grass weeds: black-grass and Italian ryegrass. Factors like temperature, weed size, and cultivation were all closely monitored to discover the optimal conditions for application to achieve the highest efficacy.

The findings from the study formed the basis of the recently updated WRAG 2021 guidelines. These outline in practical, clear terms how to administer glyphosate at the right rate, at the right growth stage and in the right conditions.

Along with the previous four actions, key recommendations include optimal growth stage to administer glyphosate, the minimum doses required, optimal weather condition or application, and the risk inherent within stale seedbeds.

Delaying resistance – a responsibility for every grower

When the tipping point of glyphosate resistance will arrive is unclear but every grower has a responsibility to help prevent and delay it. By reducing weed survivors to prevent re-application and by following the WRAG guidelines to maximise effectiveness, glyphosate can remain an essential part of grassweed control in arable crops. We must all respect what could happen if we lose it and use it wisely.

Read the full research report ‘Managing the resistance risk to retain long-term effectiveness of glyphosate for grass-weed control in UK crop rotations’.

For more information on ADAS weed related services, including herbicide resistance tests, see our Weed Management webpage.