Watch: Assessing the extent of grass weed problems on Irish tillage farms

As part of the Enable Conservation Tillage Project - a pan-European project which aimed to improve farmer and industry knowledge of grass weeds - Teagasc undertook a survey of 103 tillage farms over 2020 and 2021 to assess the extent of the grass weed problem nationally.

Vijaya Bhaskar, a Research Officer in Teagasc Oak Park, presented the key findings of this study at last week’s Teagasc and Enable Conservation Grass Weed Conference, held in Co. Kildare.

“Across the 103 farms we surveyed, bromes and wild oats were the most widespread – found on more than 50% of farms – while the likes of blackgrass and Italian Ryegrass was found on 15% of the farms, which was very concerning,” Vijaya said.

The project also determined the population pressure of each of these species on either a plough or non-inversion tillage system on the farms surveyed. Of the participants in the survey, 62 operated plough-based systems, while 41 operated non-inversion tillage operations.

Key findings on frequency and pressure:

• 53% of plough-based farms and 77% of non-inversion tillage farms had brome present;
• Many of the plough-based farms had low brome pressure compared to non-inversion tillage farms, showing that less soil disturbance tends to increase brome frequency and brome pressure compared to full soil inversion;
• 57% of plough-based tillage and 56% of non-inversion tillage farms had wild oats. With the exception of a few farms, both plough-based and non-inversion tillage farms had very low wild oat pressure at the time of the survey;
• 13% of plough-based and 12% of non-inversion tillage farms surveyed had Italian Ryegrass;
• Where Italian Ryegrass was found, especially under non-inversion tillage systems, they had the highest weed pressure and those populations were found to be resistant, showing that less soil disturbance tends to increase Italian Ryegrass weed pressure, while this may also hasten resistance development;
• Both plough (19%) and non-inversion tillage (10%) had black grass present, although at low pressure. Those populations had developed resistance;
• Of those with blackgrass present, 38% were not aware they had it until identified as part of this survey.

Prevalence of grass-weed herbicide resistance

The survey also identified the prevalence of grass-weed herbicide resistance, with Vijaya commenting: “Out of the 103 farms we surveyed, 18 farms had herbicide resistance grass weeds. Out of these 18 farms, three farms had two or more resistant species and 15 farms had a single resistant species.

“We now have resistance in plough as well as in non-inversion tillage systems and resistance has been found in all major tillage counties between the Cork, Wexford and Cork triangle.”

Additionally, he noted that resistance in blackgrass and Italian ryegrass has developed against multiple modes of action, which possesses a significant threat.

Vijaya said: “The grass weed survey has identified a number of concerns, especially the apparent speed at which herbicide resistance is developing in blackgrass and Italian Ryegrass, coupled with the resistant wild oat and the reduced sensitivity evolving in brome populations, making weed control more challenging.”

For more information on this study, watch Vijaya’s presentation from the Grass Weed Conference below: