Black-grass in a crop field

Grass weeds are a major challenge in UK agriculture and are often highly competitive in arable crops.

Some of the most common grass weeds in the UK include: Black-grass (Alopecurus myosuroides), Italian rye-grass (Lolium multiflorum), Brome (Bromus sp.), wild-oats (Avena sp.), Couch grass (Elytrigia repens), annual meadow grass (Poa annua) and Rat's-tail Fescue (Vulpia myuros).

You can find specific topic pages for black-grass and brome. See also related topics of: broad-leaved weeds, herbicidesherbicide resistance and integrated weed management

Key features of grass weeds

  • Grass weeds are monocots meaning that each seed initially contains one embryonic leaf (cotyledon)
  • Long and often narrow blades (leaves) with parallel veins
  • Stems usually hollow
  • Usually small inconspicuous spikelets (spikelets are the flowering unit of a grass)
  • Grass weeds are summer annuals, winter annuals or perennials

As many important cereal crops (oats, barley, wheat) are also grasses, it can make identification of grass weed problems challenging in the field. 'How to identify grass weeds in arable fields' on the AHDB website is a useful tool for in depth identification. 


Management options

There are a number of management options with the main ones being cultural and chemical (herbicide) control. 

Cultural control

  • A wide range of cultural control techniques can be employed specific to the targeted grass weed. This may include using optimal rotations, tillage and cultivations, suitable crop row spacing, using competitive crop varieties/cultivars and altering key timings (e.g drilling dates). 
  • The aim is to have optimal field conditions that make it more challenging for weed population establishment and growth.
  • For example delayed drilling of winter wheat is a commonly recommended to avoid the main black-grass flush.

Chemical control

  • A wide range of pre-emergence and post-emergence herbicides can be used on grass weeds - most commonly this includes ALS inhibitors (e.g sulfonylureas) (HRAC Group 2) and ACCase inhibitors (HRAC Group 1)
  • Some other pre-emergent options: HRAC Group 3 inhibition of microtubule assembly (Pendimethalin, trifluralin), HRAC Group 15 Inhibition of long-chain fatty acid synthesis (Flufenacet, tri-allate), 
  • Some other common post-emergent options: HRAC Group 9 inhibition of EPSP synthase (glyphosate)


Herbicide resistance

  • Widespread target site resistance and enhanced metabolism resistance to ALS and ACCase inhibiting herbicides has been reported across many grass weed species. Often seeing multiple resistance in populations and resistance is a growing problem.
  • This has increased the reliance on pre-emergent options and glyphosate - putting increasing pressure on weeds to become resistant to glyphosate. As such a widely relied upon herbicide, glyphosate resistance risk should be continually monitored. 
  • Genetic testing has elucidated some of the common mutations responsible for TSR in grasses. 
  • Regular monitoring and resistance testing is recommended along with integrating cultural control methods. 


Please attach any relevant projects or pages linked to grass weeds to to this topic page.

Related Organisations

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Connected Content

Herbicide resistance is the inherited ability of a weed to survive a rate of herbicide which would be lethal to a member of the normal population. It can develop over time based on repeated selection pressure imposed on the weed. This selection pressure changes the population from susceptible to resistant. Herbicide resistance is becoming an increasing problem in UK agriculture, in both grass weeds and broad-leaf weeds. See also the general topic on herbicides.

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Black-grass (Alopecurus myosuroides) is a major weed in winter sown cereals.

'Integrated Weed Management (IWM) systems in the agroecology context; new challenges.' NIAB, Cambridge, UK 24th - 26th of May 2023

Wheat is the most widly grown crop in the UK. Nationally yields average around 8 t/ha/

Herbicides are substances (usually chemical) used to control weeds in a variety of situations including agriculture, horticulture and managed landscapes. Herbicides are classified according to their mode of action (MOA) - this is the precise biochemical mechanism in which the herbicide targets and kills the weed. The 'active ingredient' of the herbicide is the specific herbicidal compound that has the phytotoxic effect and this is formulated with a variety of other ingredients (including other active substances, surfactants, buffers, adjuvants e.t.c) to make a final product which is given a trade name by the herbicide manufacturer. With any herbicide product you will find an associated product label which explains how to use the product safely and legally. This page provides an overview of herbicides including how they are classified and used. Please link any pages or projects relating to herbicide use to this topic page.  Some widely used herbicides (e.g glyphosate) also have their own topic page. Other related topics on FarmPEP include herbicide resistance,  bioherbicides, broad leaved weeds and grass weeds.  

Broad-leaved weeds are a varied group of weeds that can grow and cause significant problems in arable fields in the UK. Some of the most common broad-leaved weeds in the UK include: Common Chickweed (Stellaria media) , Scentless Mayweed (Tripleurospermum inodorum), Common poppy (Papaver rhoeas), Charlock (Sinapis arvensis L.), Fat-hen (Chenopodium album L.), Common groundsel (Senecio vulgaris), Docks (Rumex spp) and Creeping thistle (Cirsium arvense). See also related topics of: grass-weeds, herbicides, herbicide resistance and integrated weed management.

Wild-oats are a highly competitive grass-weed in the UK of which there are two important species: common wild-oats (Avena fatua) and winter wild-oats (Avena sterilis ssp. ludoviciana). Failure to control wild oats in arable fields can lead to high penalties to yield, seed crop contamination, income loss for farmers and reduced competitiveness of UK agriculture. Whilst herbicide resistance selection has been slower in wild-oats compared to other grass weeds such as Black-grass (Alopecurus myosuroides), it is still a growing problem and since this report was published in 2001, resistance has been reported across hundreds of farms across many UK counties.  Continuing development of herbicide resistance in wild-oats will limit pesticide choice and possibly lead to a higher dependence on environmentally 'risky' herbicides that are more likely to reach water. The objective of this project was to conduct and collate research on the characterisation of herbicide resistance in wild-oats with the aim of informing strategies for the prevention, containment and control of herbicide resistant populations. Links to the full project are provided at the bottom of the page.

The herbicide glyphosate was first registered in 1974 under the original trade name RoundUp (Monsanto) and has since become one of the most commonly used herbicides globally. It is a non-selective, post-emergent herbicide with a wide range of uses including arable, forestry, and horticulture.

IWM involves using numerous weed control methods to try and manage a weed problem sustainably. Whilst herbicides can still be used as part of an IWM approach, a major aim is to reduce reliance on them by also incorporating methods including, cultural, mechanical, biological, thermal and genetic control. A combination of such approaches can allow for optimal control of a specific weed problem. Related topics on FarmPEP include herbicides and herbicide resistance. You can also view the topic pages on grass weeds and broad-leaved weeds which provide examples of suitable control methods.

Crop modelling is a useful tool in agriculture to improve our understanding how a crop grows in interaction with all external factors, including environmental interactions and the crop management practices in place. The idea is that by modelling cropping system factors as a mathematical representation, and incorporating real past data to 'calibrate' the model,  you can then simulate various scenarios and predict the impacts of certain changes on crop growth. One example of this would be a simulation of predicted environmental conditions under various climate scenarios to predict the impacts of climate change on crop growth and yields. Whilst models are oversimplifications of reality and can never capture all the complexity of agricultural systems, modelling has been a vital tool underpinning key agricultural developments and models are constantly being developed to be more dynamic, complex and sensitive. One particular application of modelling is in weed control. This page highlights the application of modelling in weed management and introduces a case study of a weed model from a DEFRA report.       

Dr Stephen Moss has kindly given permission for his useful Wild-oat identification posters to be shared on FarmPEP. 

Harvest Weed Seed Control (HWSC) A project to explore harvest weed seed control (HWSC) under UK conditions as a method to control grassweeds and reduce the dependence on chemical control, particularly glyphosate.

This guidance provides an easy reference to the major broad-leaved and grass weeds in the UK, including how to identify and manage them based on an understanding of their biology.

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