In April, Teagasc confirmed the first case of glyphosate-resistant Italian ryegrass weeds in Ireland – a discovery that justifiably raised significant concerns among growers and the tillage sector.

Further testing revealed this population is also resistant to ACCase and ALS herbicides, like Axial and Broadway Star. Plants survived well beyond label application rates to all three herbicide types (Figure 1) making it impossible to control with herbicides used in cereal production.

Genetic analysis confirmed the presence of target-site resistance mutations: Pro-106 (glyphosate), Ile-1781 (ACCase) and Pro-197 (ALS). Additional investigations are under way to determine whether other mechanisms may also be involved. Biosecurity measures have been put in place to contain the problem in the affected field.

Glyphosate-resistant Italian ryegrass has previously been reported in arable crops in both Italy and the UK but this is the first confirmed case of triple resistance to all three herbicide modes of action in Italian ryegrass, posing a serious threat to weed control.

This is another wake-up call that we cannot ignore as these developments can threaten future production capacity. We must improve biosecurity to contain any problems, but we also need to adopt an integrated weed management approach.

This may include drastic measures such as crop destruction, hand rogueing or whole crop silage, if even small populations are present.

These actions will help reduce reliance on herbicides, slow resistance development, and eliminate seedbank populations. Knowing the resistance status of suspect weeds is one key step.

Test your weeds for free and confidentially with Teagasc

You can be proactive against weed resistance and get your weeds tested if you suspect resistance.

Weed Watch 2025 – The Teagasc campaign, with the Irish Farmers Journal, is back. Encouraging growers and the sector to utilise the weed seed resistance testing service for suspect populations of any grass or broadleaved weeds.

This invaluable service from Oak Park is now free for a limited time, as part of the DAFM-funded EVOLVE grass-weed research project.

Access the submission form and seed collection here.

Send ripe, dry seeds in a paper envelope with a completed form for quick and accurate results to Vijaya Bhaskar, Teagasc Crops Research Centre, Oak Park, Co Carlow.