The Teagasc team researching grassweed problems on Irish farms continue to try to evaluate the size of these problems nationally.

In the next phase of this work, they are asking for the help of growers and agronomists in tracking and mapping weed incidence and herbicide resistance problems.

This is a great opportunity to establish a detailed assessment of the presence of specific grassweed and resistance information on your farm and it can provide a great insight to help individual growers to tackle these threatening weeds.

To help get maximum value from this research, it is essential that all growers who have a problem participate in the survey flagged in this article.

If you have a problem with either blackgrass or Italian ryegrass, take five minutes to fill in the survey.

Participation will provide access to relevant information and it will also help in the understanding of the status of grassweed resistance.

The work carried out by Teagasc in recent years has identified the existence of herbicide resistance in blackgrass, wild oats and Italian ryegrass.

The team at Oak Park examining these problems includes researcher Vijaya Bhaskar and John Mahon as project adviser. I asked them what this new survey aims to achieve.

AD: Outline the information available from recent research findings.

VB and JM: The following points outline what we know and have learned to-date.

  • There is an increasing incidence of problem grassweeds, eg sterile brome, blackgrass and Italian ryegrass, which can cause yield losses of over 80% and threaten the sustainability of current cropping practices.
  • ACCase (eg Axial, Falcon or Stratos Ultra) and ALS (eg Pacifica or Broadway Star) are key post-emergence herbicide modes of action for selective grassweed control within cereal and non-cereal break crops. The only other types of active are pre-/early post-emergence herbicides (eg pendimethalin, flufenacet, tri-allate, etc).
  • Reliance on herbicides with the same modes of action can quickly lead to the development herbicide resistance. Resistance can develop in as little as three years of consecutive use of ACCase/ALS herbicides.
  • The most common resistance mechanism is target-site resistance (TSR), where the herbicide target enzyme is mutated to block the activity of ACCase or ALS herbicides. But grassweeds can develop non-target site resistance (NTSR) to multiple herbicide chemistries, where plants are able to degrade herbicides rapidly before they reach the target site. There is growing evidence that NTSR precedes TSR, resulting in both forms of resistance within a population to exaggerate the weed control challenge.
  • Failure to combat grassweed resistance will make weed control challenging and threaten production systems.
  • Further reduction in herbicide class availability means it is critical that we protect all currently available modes of action. To do this, we need to understand resistance evolution and use integrated weed management measures.
  • Has the ECT project been useful?

    We learned a lot from the Enable Conservation Tillage (ECT) project.

  • The ECT project is a five-year extension-oriented undertaking (2019-2023) funded by the European Innovation Partnership (EIP). Its core objective is to maximise knowledge transfer on grassweeds, coupled with the mapping of herbicide resistance.
  • These evaluations were conducted on suspect grassweed samples provided by growers/advisers nationally. Where resistance is suspected, testing is critical to confirm if surviving weed populations are resistant or just poorly controlled.
  • You conducted a previous survey of growers within the ECT project. What were the main findings of that survey?

    There were many different findings, but ultimately, they are summarised in the points below.

  • Research has confirmed resistance in wild oats, blackgrass and Italian ryegrass in the samples taken from Irish fields.
  • A single blackgrass plant in winter barely shows its capacity to multiply thanks to the big number of heads (over 45) and the large number of seeds per head.

  • The ECT project has significantly increased grassweed awareness and knowledge across the tillage industry.
  • A specific campaign (#blackgrass21) with the Irish Farmers Journal, launched in 2021, highlighted the extremely concerning blackgrass threat on our tillage farms.
  • How prevalent are these specific problems?

    From what we have analysed to-date from grower-submitted samples, we can confirm that we have found resistance, but we are not yet in a position to indicate the severity and scale of resistance problems. This is partly what we are trying to ascertain from the current survey and this is why we need it to be as comprehensive as possible. However, we can state the following:

  • 20 out of 123 wild oat populations collected in counties Wexford, Cork, Kilkenny, Tipperary and Kildare were resistant to at least one ACCase (Axial, Falcon or Stratos Ultra) herbicide (1A).
  • Six out of 14 Italian ryegrass populations collected in Cork, Meath, Tipperary, Kilkenny and Kildare were resistant to ACCase (Axial, Falcon or Stratos Ultra) and/or ALS (Pacifica or Broadway Star) herbicides (B).
  • 13 out of 25 blackgrass populations collected in Meath, Cork, Waterford, Wexford and Kildare were resistant to ACCase (Falcon or Stratos Ultra) and/or ALS (Pacifica) herbicides (C).
  • Will this new survey form part of another grassweed research project?

    Yes. We are now beginning a new evaluation project called EVOLVE – the main element of this is as follows:

  • EVOLVE is a four-year research project targeting grassweeds and carbon-smart cultivation systems funded by the Department of Agriculture, Food and the Marine. It is to build on the research that was undertaken in the ECT project.
  • The EVOLVE project is to focus on target-site resistance (TSR) and non-target-site resistance (NTSR) types to design effective management strategies to cope with regional resistance problems, analyse patterns of genetic differentiation within and between blackgrass populations from Ireland and the UK to infer whether resistant populations now present in Ireland were unintentionally introduced from the UK or if the resistance evolved in native populations, and establish long-term field experiments evaluating cultural and non-chemical integrated weed management practices to provide grassweed control methods that are less reliant on herbicides.
  • What will the initial priorities be in the EVOLVE programme?

    The initial priorities will hinge around getting a better understanding of the prevalence of these weeds and in particular the occurrence of herbicide-resistant strains.

  • We need more information on blackgrass and Italian ryegrass in particular, so we are starting the project by asking growers or agronomists who suspect they may have these weeds to contact us, using the confidential survey link.
  • If you suspect that you have these weeds, we will contact those who complete the survey to help confirm identification and to arrange for collection of viable seed samples.
  • These will then undergo resistance testing (TSR and NTSR) for the main herbicide groups; the genetic changes underpinning resistance type and the source of the blackgrass populations will be assessed. The frequency and distribution of herbicide-resistant blackgrass and Italian ryegrass will be mapped across the country to help make other growers aware of their potential risk.
  • Following the assessments, each grower will be provided with the results and control options for their situation.
  • The results and knowledge gained will benefit the whole tillage sector.
  • How do you access the survey?

    The actual online survey can be accessed here.

    The survey should take no more than five minutes to complete and the confidentiality of each submission is assured. Details on the completion of the survey and how the collected data will be used is included in the survey.

    Resistance testing is crucial on each sample to determine if the population is resistant, what form of resistance is present and to identify the most effective chemistry to offer effective control for your populations.

  • Previous grassweed research has identified the existence of herbicide resistance in different grasses in parts of the country.
  • A new research project aims to expand on this knowledge to identify the prevalence of different resistance types around the country.
  • Detailed knowledge of individual populations is essential to guide the most appropriate control strategy, especially the use of herbicides.