Teagasc Crop Report

Tillage Grass Weeds

Tillage Grass Weeds

Friday 17th January 2020
(Updated Thursday 13th October 2022)
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Wild Oats

Wild oats

There are two types of wild oats.  Avena fatua (Spring wild oat) and Avena sterilis (Winter wild oat).  Fields generally have spring wild oats but occasionally fields can have a mix of spring and winter wild oats. Wild oat

Identifying both species (See pictures here)

Avena fatua (Spring wild oat)

  • Awns present on third seed within spikelet
  • Seeds separate when mature and shed singly

Avena sterilis (Winter wild oat)

  • Awn absent on third seed in spikelet
  • Seeds remain attached when mature and shed as a unit 

Spring wild oats

This is the most common type of wild oat in Ireland.

  • Predominately spring germinating, but odd seedling germinate from September to May.
  • Have the ability to survive in soil for several years and thus unaffected by seed burial depth.
  • Plants set seeds from Jun to Oct and light promotes germination.
  • Most seeds emerge from the top 10 cm soil, but some emerge from greater depths, up to 15 to 25 cm.
  • A single well-tillered plant has the ability to produce up to 2,000 seeds.
  • A population of 1 plant per m2 has the potential to cause a yield loss of 1%

There is now confirmed Herbicide Resistance to most of the major herbicide types 

Brome weeds


Sterile brome is the most common grass weed of the brome family.  However Soft,  Great , Meadow and Rye brome are present in many Irish fields also.

Correct identification of these bromes is critical to achieving good control.  Each brome has specific identifying characteristics with identification becoming easier when the plant is headed with mature seeds.  

Sterile Brome 

Sterile brome is the most widespread weed, found with a range of fertile soils throughout Ireland.

Sterile brome is native and widespread in Ireland. It’s not hard to recognise as its familiar purple, drooping heads are seen towering above cereal crops and around hedges each June and July. It’s an annual grass weed which means a plant must germinate from a seed every year. Its natural habitat includes verges, field headlands and waste ground. It grows freely on waste or cultivated land on well-drained soils. It is competitive in winter wheat and winter oilseed Rape. It can cause a yield reduction in wheat of 2.4% with just 3 plants/m2. It is increasing problematic on arable land that is in continuous cereals especially winter barley where herbicides options are minimal. Brome has no auricles.

Scientific classification:









Key identification features

Sterile brome from a young plant has a hairy stem and leaves, it has a dense covering of hairs on the stem and leaf surface. It is easy to spot in barley crops due to its twisted slender leaf appearance; it is more difficult to distinguish from wheat crops due to the twisted leaf and slender leaf structure of the wheat plant. The key feature to look for is the hairs on the stem and leaf, a magnify glass is sometimes required to see the hairs especially on young plants. It helps to roll the leaf over your finger and hold it up to the light to see the surface of the leaf hairs.

It must be noted that all bromes have hairs so furthermore identification may be required, if possible finding the seed that the plant emerged from can be a good indicator but it is sometimes hard to differentiate between the different bromes.

The ligule is like a barcode for grass weeds, the ligule of each plant differs allowing for accurate identification. To find the ligule of a plant is quite simple, it can be seen at the stem where the leaf has the left the stem.

Key features

  • About 90 % of sterile and great brome germinates from Aug to Dec; it flowers from May to Jul and shed seeds from Jul to Aug.
  • Other bromes, especially soft (relic of Irish grassland), meadow and rye germinate in the autumn, but also in early spring.
  • Sterile and great brome requires vernalisation to produce seeds and these readily germinate in darkness, while soft, meadow and rye brome seeds require a period of post-harvest ripening and light to induce germination.
  • Sterile brome
    - Can produce and average of over 200 seeds but this can range from 5- 300 seeds per plant.
    - Seeds have poor persistent in the soil.
    - Seed emergence is reduced with increasing seed burial depth (> 10 cm).
    - 5 plants per m2 can cause yield reduction of 5 %.

Seeds statistics;

  • Seed longevity >1 -5 years
  • Seed decline > 90% per year
  • Germination depth > Once the seed is covered up to 5cm deep
  • Flowers per plant > 4 - 10
  • Seeds per flower > 200
  • Seeds per plant > up to 2000

Great Brome

Scientific classification

Kingdom  Plantae
Family Poaceae
Genus  Bromus
Species B.diandrus


Great brome has been found in some areas of Ireland but is not as dominant as sterile brome. However its often underreported partially due to mistakenly identified as sterile brome in some cases. Similar to sterile, great brome is found in field margins, waste ground and roadsides. It usually prefers a sandy soil and dunes.

Herbicide Resistance Update

Herbicide Resistance

  • Herbicide resistance is defined as ‘the evolved ability of a weed population to survive a maximum dose rate of herbicide that was previously known to be lethal’.
  • Resistant weed populations may by-pass the herbicide action by two mechanisms: target-site resistance (TSR), where simple mutations prevent the herbicide from binding effectively to its site of action and non-target site resistance (NTSR), where complex multigenic changes, allow the weed to metabolically detoxify or degrade the herbicides to an extent where they are ineffective.
  • Resistance is further exacerbated by the lack of alternative herbicide types, forcing growers to repeatedly use the same active ingredients.
  • Herbicide resistance is a global problem with 500 unique resistance cases being reported, globally until 2019.
  • Herbicide Groups A (ACCase) and B (ALS) pose a very high risk of resistance.
  • NTSR has been reported to be the common type of resistance to glyphosate, and also plays a key role in resistance to ACCase and ALS inhibitors. Although, NTSR is slower to develop, NTSR resistant weeds are widespread in major tillage crops. For example, chlorotoluron and pendimethalin actives can affect NTSR to some degree.
  • Herbicide resistance can also occur through spread of resistant genes, in contrary to independent-endowing mutations.
  • Sensitivity tests are valuable to provide direction to correct management strategies

First Report on Assessing the Severity of Herbicide Resistance to ACCase Inhibitors Pinoxaden, Propaquizafop and Cycloxydim in Six Wild Oat (Avena fatua) Populations in Ireland

Spring wild oat populations were tested for resistance to ACCase inhibitors pinoxaden (DEN or Axial) , propaquizafop (FOP or Falcon) and cycloxydim (DIM or Stratus Ultra) was investigated in populations of six Spring wild oats, Avena fatua collected from cereal-dominated rotations in Ireland.

Glasshouse assays confirmed reduced sensitivity to all three ACCase inhibitors in four of the populations tested. R1 population was cross-resistant to pinoxaden and propaquizafop and R6 was resistant to propaquizafop only.

Dose-response studies confirmed significant differences in resistance levels amongst these populations (P < 29 0.05).

  • For pinoxaden, the ED50 or GR50 resistance factor (RF) of population R1, R3 and R5 were between 11.6 and 13.1 times or 25.1 and 30.2 times more resistant, respectively, compared with the susceptible populations.
  • For propaquizafop, the ED50 or GR50 RF 32 of populations R1, R2, R3, R5 and R6 were between > 7.8 and > 32 or 16.6 and 59 times more resistance, respectively compared with the susceptible populations.
  • For cycloxydim, only population R5 had both the ED50 and GR50 RF exceeding > 43.2 and 98.4 times compared with the susceptible populations.

In population R2, although the ED50 values to both pinoxaden and cycloxydim and additionally, population R3 to cycloxydim, were above recommended field rates, their GR50 values remained below, suggesting a shift towards cross resistance.

While population R4 was the only population, where both ED50 and GR50 for all ACCase inhibitors remained below recommended field rates, but they would not give effective control at these rates, strongly indicating evolving resistance.

This is the first study reporting variable cross-resistance types and levels to ACCase inhibitors in A. fatua from Ireland.

The full results are available here


Grassweed Herbicide Resistance 2021

The ECT project has collected plant seeds from around the country both as part of a large survey of growers and also from concerned industry, agronomists and farmers.

 To date, 34 field populations of wild oats have been identified with herbicide (ACCase) resistance, since the first case was verified in 2016. To investigate the linkages between management actions, weed pressure and the incidence of resistance further, a nationwide survey of 145 farms was conducted from June to September 2020 as part of the on-going ECT project.

The survey included a questionnaire, grass weed assessments, and the collection of seed samples for herbicide resistance testing.

Glasshouse studies on 12 populations of sterile brome, identified a larger variation in susceptibility within and between populations to reduced rates of ALS-meso+iodosulfuron (Pacifica® Plus®) or ACCase-cycloxydim (Stratos Ultra®). This may indicate resistance evolution, which will likely accelerate with the repeated use of rates lower than the recommended label rates.

Studies with 14 populations of black-grass indicate the presence of resistance to both ACCase and ALS herbicides. 



To limit the spread of resistant grass weeds, an integrated management approach with judicious herbicide use (e.g. using label rates) must be deployed to minimise seed return and ensure effective control with a limited herbicide armory remains possible in the future.

Anyone who suspects that they have a herbicide resistant grass weed on their farm can send samples into the Enable Conservation Tillage project in Oakpark. When submitting a sample for testing please fill in the information on the Grass Weed Seed Collection Form and follow the sampling protocol to ensure that the sample provided is suitable for testing.


Arable Grass Margins

Grass Margins - Arable fields

Arable grass margins are areas from 1.5 - 3 meters between the main crop and the field boundary deliberately managed to (a) provide habitat for flora and farmland wildlife species, (b) add biodiversity value and ecosystem services, (c) protect water quality, and (d) most importantly, compete with problematic grass weeds like sterile  brome, which are increasingly problematic along field boundaries and invading into fields. Control of sterile brome in margins/hedges by total weed control or selective graminicides have controlled competitive  species and allowed bromes to flourish rather than decreasing their incidence. Continuous mowing encourages seeding at lower levels. Teagasc Oak Park have demonstrated that a margin specifically sown with competitive perennial grasses when properly managed, provides competition for the sterile brome by preventing their regrowth, and therefore seed return.  Click on the picture below to read more.

Grass Weed Susceptibility Table - Cereals Post Emergence

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