Best Practice Information Sheets (Westcountry Rivers Trust)


Pest management

Best Practice
Information Sheet

Managing weeds

IS 2.6.2

Why change?


Grass weeds and herbicide resistance are of increasing concern in autumn planted arable systems. Combine your use of herbicides with cultural techniques including stale seedbeds, crop rotation, delayed drilling and rotational ploughing to benefit from reduced costs, and:

  • improved crop yields and quality
  • reduced risk of herbicide resistance
  • reduced risk of watercourse pollution and negative publicity
  • more effective herbicide use
  • improved biodiversity.


Steps to success

  1. Review the current situation by assessing the weed species and populations on your farm. Consider the success of existing chemical and cultural controls across the whole rotation. Check individual fields regularly to assess weed species and populations and respond quickly to any problems.
  2. Identify potential opportunities for improved management of weeds on your farm. For example, if you practice cereal monoculture, early autumn sowing or reduced cultivation, or have high weed infestations, you may need to pay special attention to weed control. Consider the scope for balancing cultural controls such as crop rotation, stale seedbeds and late drilling with your chemical use. Use a BASIS-qualified agronomist for advice on integrated pest management and pesticide recommendations.
  3. Calculate the cost-benefit of these opportunities by considering the cost of management changes versus the savings such as improved crop yields and quality, and more effective herbicide use.
  4. Develop an action plan for improved management of weeds on your farm:
    • refer to Cross Compliance regulations, Good Agricultural Environmental Condition (GAEC) 11, and comply with the Weeds Act 1959.
    • know the distribution and germination periods of the weed seeds in your soils
    • plan your weed management strategy across the whole rotation using a combination of chemical and cultural techniques. Pay particular attention to herbicide resistant species such as black-grass, Italian rye-grass and wild oats. Make pre-harvest weed maps to determine future weed control needs
    • choose and use herbicides with care. Assess leaching, runoff, persistence and herbicide resistance risks. Avoid herbicide drift into watercourses and wildlife habitats such as buffer zones, beetle banks, hedgerows and woodlands
    • use crop rotation to vary herbicide chemistry and reduce weed levels by 60% or more
    • use rotational ploughing on a 1 in 3-year basis to bury weed seeds. Bury the seed at a known depth (e.g., below 12-17cm for large-seeded grass species) and cultivate more shallowly afterwards. Time your ploughing according to the weed species, to allow seeds to ripen and avoid enforcing dormancy. Make sure soil is fully inverted and that seeds are not flicked across the soil surface
    • use stale seedbeds where possible, especially to prevent build-up of grass weeds under reduced cultivation
    • make use of timely operations to control weeds. For example, early-sown oilseed rape will out-compete weeds, whilst delayed drilling in winter cereals allows crop volunteers and autumn germinating weeds time to emerge. These can then be removed using a non-selective spray such as glyphosate prior to drilling. Remember to avoid drilling wet, heavy and erosion-prone soils in order to minimise soil damage and runoff
    • match weed control to potential crop losses. Target aggressive weeds first. Consider leaving residual levels of non-aggressive weeds in crops for the benefit of wildlife
    • consider using weedwipers and weed burners for small quantities of weeds or in conservation areas.



Best Farming Practices: Profit from Change

Practical examples

Strategy for developing a stale seedbed

Use the following sequence to create a stale seedbed as part of an integrated approach to weed management:


  • post-harvest crop residue incorporation
  • create a medium quality seedbed
  • consolidate
  • wait for weed germination
  • spray a non-selective herbicide such as glyphosate to control weeds
  • drill within 2-3 days.

Tolerance index of some common arable weeds (numbers of plants that reduce winter wheat yields by less than 5%)


  Tolerance index Weed


Not tolerated Barren-brome, black-grass, cleavers, couch, Italian rye-grass, meadow brome, wild oats


20-49 weeds/m2 Charlock, mustard, mayweed, oilseed rape, poppy, thistle


20-49 weeds/m2 Campion, chickweed, fat-hen, forget-me-not, redshank



50-99 weeds/m2


Annual meadow grass, cranesbill, fool's parsley, fumitory, groundsel, knot grass, red dead-nettle, scarlet pimpernel, sow thistle, speedwell, wild onion


Over 100 weeds/m2 Black bindweed, field pansy, parsley piert, venus's-looking glass
(Adapted from Defra Arable Cropping and the Environment)




  • Planning and timeliness are essential to successful weed management. Integrate your use of chemical controls with cultural measures for a balanced, cost-effective and long-term approach.
  • A herbicide resistance management strategy is extremely important in reduced cultivation systems, and where very high weed levels exist.
  • For further information: Defra (08459 335577,, Environment Agency (08708 506506), ECSFDI (0800 5874079), and



Disclaimer - Whilst the Westcountry Rivers Trust, its servants and agents (the "Trust") will use its reasonable endeavours to ensure the accuracy of its work, its advice involves matters relating to the natural environment or matters outside its reasonable control. Accordingly, other than personal injury or death arising from its negligence, the Trust will not be liable for any loss or damage howsoever arising directly or indirectly from any act, omission, neglect or default on its part. Funding for updating these information sheets was provided by the Water Quality Division of Defra as part of its England Catchment Sensitive Farming Delivery Initiative. These sheets provide practical information, guidance and recommendations for farmers based on Trust experience. © Westcountry rivers trust, 2007.

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