Teagasc is reporting that a second glyphosate-resistant Italian ryegrass population has been found in Ireland.

This follows the first confirmation of the issue in 2025.

Glyphosate resistance within Italian ryegrass populations raises significant concerns for the tillage sector.

Full testing by Teagasc of 2025 resistance-suspect Italian ryegrass samples to post-emergence foliar herbicides has now been completed, with the detection of a second glyphosate-resistant strain representing a significant escalation in resistance risk.

The second resistant ryegrass population has been categorised as IRG-19.

The ryegrass was tested with glyphosate at 720g/ha and 1080g/ha, surviving both application rates.

Moreover, unlike the first confirmed glyphosate-resistant population, which exhibited resistance to ACCase, ALS, and glyphosate-based herbicides, IRG-19 is resistant only to ALS herbicides (Pacifica and Broadway) and glyphosate.

A target-site mutation at EPSPS Pro-106, associated with glyphosate resistance, was detected in IRG-19.

This was similar to the mutation detected in the first confirmed case. Further investigation by Teagasc scientists is ongoing.

To date, Italian ryegrass has been identified in 67 fields, of which 53 (79%) are confirmed as resistant. Italian ryegrass remains a serious and growing threat to crop production, Teagasc said.

On-farm biosecurity

According to Teagasc research scientists, this situation serves as a wake-up call, as the spread of complex multi-resistant populations threatens future production capacity and the wider industry.

Improved on-farm biosecurity is essential to contain these issues, the research scientists said, alongside the adoption of integrated weed control strategies.

These strategies include extreme but necessary measures such as crop destruction, hand rogueing, or whole-cropping, even where infestations are small.

Such actions are critical to reducing reliance on herbicides, slowing the development and spread of resistance and preventing further replenishment of the seed bank, Teagasc said.

Straw imports from Britain have been increasingly highlighted as sources of herbicide resistant weeds that will have a major impact on Irish crop production.

The list here includes Italian ryegrass and blackgrass.

Integrated pest management strategies

This has come at a time when the number of new herbicide chemistries coming to market has dropped off alarmingly.

The use of integrated pest management strategies will be key to the future control of weeds within Ireland’s tillage sector.

Driving this will be the implementation of crop rotations that will allow growers to use physical weed control systems more effectively.

There is also a requirement to maintain the full availability of the herbicide chemistries that remain on the market.

Making this happen will require the use of herbicides at the appropriate time and growers using full application rates only.