Blackgrass in a Wheat crop

A weed can have many definitions, one being, any plant growing in a place it is not wanted. This topic focuses mainly on weeds affecting agriculture.

Generally weeds are classified into two groups: grass-weeds (e.g Black-grass, Italian ryegrass, Bromes) and broad-leaved weeds (e.g Mayweed, Chickweed, Poppy, Cleavers). 

Weeds can cause numerous problems to agriculture including:

  • Reductions in yield
    • Taking resources from the crop – nutrients, sunlight, and water
  • Impacts on crop quality
    • E.g. Charlock causing high euric acid in Oilseed rape
  • Harvest issues
    • Combining e.g. cleavers, bindweed
    • Root crops e.g. Fathen blocking harvester slats
  • Crop storage problems
    • Act as a host for pathogens and pests
  • Impact on livestock
    • Reduced feeding - thistles
    • Milk taint – wild garlic

Weeds can be controlled using many different methods, including:

  • Crop rotation
  • Cultivations
  • Hygiene
  • Hand removal (Rouging)
  • Increased crop competitiveness
  • Mechanical control
  • Chemical control - see linked topic on herbicides

Weeds can persist in soil for many years. The scale of effect from the weed is influenced largely by the weed species, weed density and time of emergence relative to the crop. Understanding the biology of the weed species present is essential to identify weak points in its lifecycle and offer efficient control options, it is therefore key to identify weeds correctly.

Share any useful resources or tools for weed identification and management below.

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Integrated Pest Management highlights the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms. IPM is one of the tools for low-pesticide-input pest management, and IPM must now be implemented by all professional agchem users.

An EU-wide network to support and promote solutions for alternative weed control.  

Derived from natural materials such as animals, plants, bacteria and certain minerals. Designed to affect only one target pest and often decompose quickly. 

ADAS scientists help evidence and guide crop disease management by chemical, genetic and biological approaches. Our expertise covers all areas of disease management on the major crops. We lead multi-organisation collaborative research into disease management and preventation, as well as provide strategic consultancy.  

This Open Access chapter describes the current status of IWM for grasslands. Its focus is on mana

Integrated farming is a type of farming that aims to maximize the efficiency and productivity of the farm by integrating different types of crops and animals into a single system.

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.

Brome grasses are becoming an increasing problem in arable cropping systems.

This Topic doesn't yet have a Stewarded summary, but connected groups, content and organisations show below. Click the 'Ask to Join' button if you would like to be a Steward for this Topic and provide a summary of current knowledge and recommend useful resources, organisations, networks and projects. "Like" this Topic if you would like to see it prioritised for providing a wikipedia style summary.

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

This field lab was initiated as part of the ADAS project ‘Investigating the distribution and presence, and potential for herbicide resistance of UK brome species in arable farming’, funded by AHDB.  

App and website dedicated to pest, disease & weed identification and management.

Online guide to identifying arable weeds from ADAS, AHDB and BASF

AHDB Guide from 2021 incorporating WRAG guidelines. Weed control is vital for high yields of good-quality crops and to prevent the spread of pests and diseases, e.g. ergot. Yet with fewer active ingredients, a need to protect water and manage herbicide resistance, the weed challenge must be managed across the rotation.

TALISMAN and SCARAB were long-term projects developed to follow on from issues raised in the Boxworth project. TALISMAN focused on the economic issues of reducing pesticide and fertiliser use, whilst SCARAB examined the ecological side-effects of pesticides.

This Open Access chapter describes the current status of IWM for grasslands. Its focus is on management practices available to influence transitions in a weed’s life cycle: from the soil seed bank to seedling establishment, from the seedling stage to the mature plant, and from the mature plant to the soil seed bank.

Talk by Alastair Leake at IFS Agronomic Conference 2021. Farming systems employ differe

The Weed Resistance Action Group (WRAG) produces guidance on pesticide resistance issues. Hosted by AHDB, this information can be used to help protect crops and the long-term efficacy of herbicides.

This Topic doesn't yet have a Stewarded summary, but connected groups, content and organisations show below. Click the 'Ask to Join' button if you would like to be a Steward for this Topic and provide a summary of current knowledge and recommend useful resources, organisations, networks and projects. "Like" this Topic if you would like to see it prioritised for providing a wikipedia style summary.

Agrochemicals are chemical products used for agricultural purposes. Although agrochemicals have high input costs, they are widely used in the farming industry for their beneficial effects on crop yields and quality and associated reduced labour costs. Together with advances in agricultural machinery and infrastructure, the use of agrochemicals played a large role in the Green Revolution. This was a period in the 21st century in which the spread of various agricultural technologies led to greatly increased yields and production globally. However, a number of concerns around agrochemicals exist including negative effects on human health and the environment and the development of pest populations that are becoming resistant to them. A major challenge of modern agriculture is to try and reduce reliance on agrochemicals whilst continuing to increase yields and feed a growing global population.

An ADAS report to DEFRA in 1998 highlighting key trends and research priorities for the sunflower industry in the UK Sunflowers (Helianthus annuus var. macrocarpus) are in high demand due to the culinary, confectionary, bird-seed and industrial uses of their seeds (and thus oils), in addition to the popularity of the flowers in horticulture. At the time of this report in 1998, the UK imported ~350,000 tonnes of seed annually.  Whilst sunflower can be grown in the UK, there are a number of challenges including limited drilling dates to comply with soil temperature requirements, and careful monitoring of a range pests and diseases that sunflower is susceptible to. Further risks such as a late harvest time and the possibility of sunflower itself becoming a weed in following crops meant many farmers were not considering growing sunflowers on their farms. Based on a survey of UK farmers (including both sunflower growers and non-growers), the key factors reported that would encourage more UK farmers to adopt sunflower crops were… To convince farmers of profitability Guaranteed establishment of the crop Earlier harvests Good disease and weed control More information on growing the crops This project provided a comprehensive review of growing sunflower as an arable crop in the UK.  You can find the entire report linked at the bottom of this article (including historical and market information on sunflowers) but some of the key sections are highlighted here. Note all information is accurate for the time of this report (1998).

AHDB Guide published in 2018.

A 1998 study commissioned by the Pesticides Safety Directorate to assess the non-target impacts of pesticides on non-target terrestrial plants (NTTP's).  'To conserve and enhance biological diversity within the UK' was a stated aim of of the UK Biodiversity Action Plan (1994). Over 25 years later this is still a vital issue and the UK has stated its commitment to secure a post-2020 Biodiversity Framework as well as developing a 10 point plan for financing biodiversity (UK Government, 2022). However, a threat to plant biodiversity is non-target effects of pesticides - this is when pesticide materials reach areas beyond the target application area and affect the species there. Effects of pesticides on non-target plants can range from lethal (death of the plant) all the way to enhanced growth of these plants. Such varied effects depend on a range of things including the type of pesticide used, the concentration of its active ingredient and the sensitivity and spatial range of affected plants. Importantly, plants are part of complex food and pollination webs and so pesticide effects on plants can have cascading effects on the fauna that rely on them, and vice versa.

Innovative Farmers are launching a new field lab exploring the use of poly cropping, inoculants and undersown cover crops to control blackgrass (BG) in spring and winter-sown crops.  

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.

As grass-weed herbicide options in oats are limited, it is especially important to use integrated pest management (IPM). Organic systems, with their focus on cultural control – use of rotation, stale seedbeds and mechanical weeding – provide valuable lessons for control in conventional crops.

COVER CROPS USE ACROSS EUROPE

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.

Written By James Clarke - ADAS Research Director

Biofumigation involves incorporating brassicaceous cover crops into the soil.

PGRO Chief Executive Roger Vickers talks us through one of PGRO's intercropping trial plots.

Creeping thistle has become an increasing problem especially for organic arable farms with soils of higher organic matter content.

A new paper published by ADAS summarises evolving black-grass herbicide resistance over the last 35 years, including the effectiveness of the dwindling actives left, and the vital role of routine resistance testing.

Docks are perennial weeds that compete with forages of nutritional importance for livestock production.

AHDB Publication 2018.

AHDB BBRO Review 2019 Research Review No. CP 182 / 1807258 - Review of weed control options

AHDB Report 636 from research project into Brome, reported September 2021 by Sarah Cook,

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