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Grass Weed Control

Controlling weeds is vital if farmers are to produce high yielding, good quality crops. Weeds compete for nutrients, light and water and if left uncontrolled will cause problems not just in the current crop but in subsequent crops as well.

There are a number of agronomic factors which can increase the grass weed challenges on farm.

These include:

Continuous cereal cropping or insufficient crop diversification

  • Earlier sowing of autumn-sown cereal crops
  • Lack of harvest and cultivation machinery hygiene
  • Lack of headland and field margin management
  • Heavy-dependence on chemical control
  • Herbicide application at inappropriate timings
  • Using reduced rates of herbicides
  • Use of herbicides with the same mode of action for successive cropping seasons on the same field

Heavy reliance on herbicides for weed control has never more unsustainable. The loss of key active ingredients and the limited number of new products being brought to the market is compounded by the rise of herbicide resistance found in a number of the key grass weeds which affect arable crops. This makes the use of IPM even more important, the grass weed challenge must be managed across the length of the rotation.

Integrated Weed Management

One key to managing grass weeds and to minimise the selection pressure for resistance, is to diversify or integrate weed management practices beyond using herbicides. Integrated weed management (IWM) combines non-herbicide or cultural techniques, which should be implemented first, with herbicide used when needed.

 Graphic illustration of the components of Integrated Weed Management all information in table below

Components of Integrated Weed Management

IWM also targets weed seed bank reduction and prevents weed movement to different areas. IWM encourages farmers to: keep fields free of specific weeds; reduce the pressure on herbicides and prevent seed return. Correct weed identification coupled with an understanding of their agro-ecological traits is of paramount importance in devising effective IWM programmes.


 The “5 for 5” Blackgrass campaign (AHDB 2017) is an example of an Integrated Weed management strategy.

Current herbicide options for cereals in Irish tillage farms

Utilising all the tools available to a farmer includes using herbicides.  Due to; the limited number of active ingredients available, the loss of actives due to EU legislation and the increase of herbicide resistance, this project aims to help farmers minimise the use of herbicides, while at the same time, where a herbicide application is necessary, optimise the effectiveness of the herbicide. 

Table 1 – Common herbicides used for grass weed control

ProductActive ingredients     HRRC MOA class and group                      Application Timing                   Weed Susceptibility*                       Crops
DefyProsulfocarbLipid synthesis (N)Pre & Post  (x)(x)WW,WB
FirebirdDiflufenican + Flufenacet             PDS (F1), VLCFAs (K3)Pre & Post  (x) WW.WB
Firebird Met*Diflufenican + Fluenacet + Metribuzin             PDS (F1), VLCFAsPre & Post  (x) (x) WW,WB 
Tower Chlortoluron + Diflufenican + Pendimethalin Photosystem II (C2), PDS (F1)  Pre & Post    WW,WB
Pontus Flufenacet + Picolinafen VLCFAs (K3), PDS (F1) Pre & post    WW,WB 
Stomp Aqua Pendimethalin Microtubule inhibitors (K1) Pre & post     WW,B 
Flight Pendimethalin + Picolinafen Microtubule inhibitors (K1),  PDS (F1) Pre & post     WW,WB
Bulldog Pendimethalin+ Diflufenican Microtubule inhibitors (K1), PDS (F1) Pre & post     W,B 
Alister FlexDiflufenican + Mesosulfuron-methyl +  Iodosulfuron-methyl 

PDS (F1), ALS (B) 

Post  (x) (x)  WW 
MonolithMesosulfuron + Propoxycarbazone ALS (B) Post  WW 
Pacifica PlusAmidosulfuron + Mesosulfuron-methyl + Iodosulfuron-methyl-sodium ALS (B) Post  WW 
Broadway StarPyroxsulam + Florasulam ALS (B) Post  (x) WW 
AxialPinoxaden ACCase (A) Post  (x)  W,B 
FalconPropaquizafop ACCase (A) Post (x) (x)  OSR, Beans, Po, FB 
Stratos UltraCycloxydim ACCase (A) Post (x)  OSR, Beans, FB 

MOA – mode of action;

Pre- pre-emergence, Post- post-emergence;

(x) - not specified on label;

*Available autumn 2021;

Weed susceptibility* - check label for growth stage and susceptibility rating;

BG – black-grass, CG – canary grass, SB – sterile brome, WO – wild oats;

WW – winter wheat, WB – winter barley, W- winter and spring wheat, B – winter and spring barley, OSR – Oilseed rape, Po – Potatoes, FB, Fodder beet