Annual meadow-grass is abundant in all tillage fields and is a major problem on many farms. Action to control this weed needs to be taken early, as leaving control until springtime can make the problem worse.

It is primarily a self-pollinating grass, germinating all year round, with peak emergence from April to September. It hardly ever grows in isolation and is often found with broad-leaved and other grass weeds.

In most years, it is considered a lower-priority weed in weed control programmes, due to its relatively modest impact on crop yield compared to other weeds.

However, in recent years, particularly since the removal of IPU from the market, its control has become more difficult in winter crops.

Additionally, herbicide-resistant populations are now present in Ireland, with some herbicides (eg, ALS-Pacifica) no longer able to control annual meadow-grass.

Farmers now need to pay more attention to prevent resistance build-up in the grass weeds on their farm.

The following practices can result in poor control of annual meadow-grass

  • Continuous winter cropping;
  • Early sowing of winter wheat;
  • Non-inversion tillage, especially in a wet year;
  • Poor early-season weed control;
  • Using glyphosate at sub-optimal rates;
  • Not using autumn residual herbicides or using herbicides with a poor activity on annual meadow-grass (eg, DFF);
  • Relying solely on a spring application of a broad spectrum herbicide, like ALS-Pacifica, to control problem grass (including annual meadow-grass) and broad-leaved weeds.
  • For winter crops: spring herbicides should not be the first option

    Remember, in winter cereals, post-emergent spring herbicides should only be used judiciously – to tidy up any remaining weeds following autumn treatments, or, if necessary, as a follow-up treatment to prevent weed problems from later-emerging plants.

    Not using autumn herbicides and relying completely on a spring application for weed control will render spring herbicides ineffective and highly vulnerable.

    Chemical options to control annual meadow-grass

  • Glyphosate (at least 1.5L/ha or above) can be applied – before sowing the crop – to kill all emerged plants.
  • Residual herbicides, applied at full label rates at pre-emergence or early post-emergence is the most effective way to control annual meadow-grass.
  • Use stacked (Table 1) or tank-mix flufenacet or pendimethalin-based products (eg, Firebird, containing flufenacet and DFF, along with Defy, containing prosulfocarb) no later than when plants have one to three leaves emerged.
  • For spring barley crops, some of the pendimethalin-based products (eg, Stomp Aqua) are also available for use.
  • Remember, DFF predominantly provides broad-leaved weed control with some annual meadow-grass activity, so when used alone it will result in poor grass-weed control.
  • ALS-type herbicides applied at full-label rates are the only available post-emergent option to control annual meadow-grass in late autumn or spring (Alister Flex – up to GS29; Monolith – up to GS25; Pacifica up to GS31), and this is only practicable in winter wheat crops (see Table 1).
  • Although, most susceptible grass-weed populations are sensitive to ACCase herbicides, annual meadow-grass shows natural tolerance to Axial, Falcon and Stratos Ultra, due to the inherited target mutation point of ACCase. Despite this natural trait, ACCase-Centurion Max still provides effective control.
  • First ALS-resistant annual meadow-grass

    There is only one confirmed case of ALS-resistant annual meadow-grass in Ireland to date. It was found in a continuous winter wheat field in Dublin (Figure 1).

    However, more cases have been seen in fields this season – confirmation is, however, still needed from the laboratory.


    A population from Dublin resistant to Broadway star.

    A population sensitive to Broadway star.

    A population sensitive to Pacifica Plus.

    A population from Dublin resistant to Pacifica Plus.

    So far, resistance has been found in ALS herbicides – Pacifica and Broadway Star (not registered for annual meadow-grass control).

    Annual meadow-grass has been found to have developed resistance to 10 different herbicide modes of action (including glyphosate, propyzamide, pendimethalin, etc), ranking it as the third most important herbicide-resistant weed, internationally.

    Reduce the risk of resistance development

  • Delay drilling and use one or two applications of glyphosate as part of a stale seedbed strategy.
  • Increase seeding rate, especially when planting late or in less than ideal conditions.
  • Include spring crops in the rotation.
  • Include non-cereal break crops (eg, winter oilseed rape).
  • In OSR, use Katamaran (metazachlor) pre-emergence for annual meadow-grass control.
  • In OSR, use Kerb (propyzamide) for early post-emergence control of volunteer cereals and other problem grass (including annual meadow-grass) and broad-leaved weeds.
  • Where control is poor, use Centurion Max (Clethodim) as a follow-up.
  • Spray as early as possible, ideally with pre-emergence, or at the latest early post-emergence with a residual herbicide.
  • Ploughing – it can reduce grass weed populations, but not always.
  • Strategic spot-spraying.
  • Keep machinery clean from one field to the next.
  • Establish perennial-grass-based mixtures in field margins.
  • In brief

  • Multi-pronged attack early in the season is key to managing grass weeds, especially annual meadow-grass.
  • Ensure correct actives and effective products; correct application timing and robust herbicide rates for maximum efficacy.
  • Spring herbicides should not be used as the main herbicide in winter crops, and only in a tidy-up situation.
  • A grass-weed conference will be held on 8 November in the Killashee Hotel, Naas, covering herbicide resistance, cultural control options, and results from research projects.