Top tips to manage herbicide-resistance risks in arable weeds

Herbicide resistance is an irreversible process – once present, it does not disappear (even if the herbicide is no longer used). However, you can slow its development, in rotations dominated by autumn-sown cereal crops, by following these tips.

Arable weed management home

Introduction to herbicide resistance in arable weeds

Weed Resistance Action Group (WRAG)

Top tips to reduce herbicide-resistance risks

  • Manage resistance threats – even before herbicide efficacy declines
  • Reduce reliance on herbicides – a change of herbicide policy alone is unlikely to provide adequate lowering of resistance risk
  • Adopt non-chemical control methods
  • Maximise the benefit from pre-emergence herbicides, which are associated with partial and relatively slow resistance development
  • Place less reliance on post-emergence herbicides – regular use of ACCase-inhibiting and ALS-inhibiting herbicides is associated with a high risk of herbicide resistance
  • Where possible, use lower resistance risk post-emergence herbicides in the rotation (e.g. propyzamide and carbetamide) in oilseed rape and beans
  • Note that residual herbicides require moisture and an even seedbed for good efficacy, and most do not perform well in high organic matter (over 5%) soils
  • Where soil does not cover crop seed (e.g. in no-till establishment systems), do not apply herbicides until the crop has established.
  • Use mixtures and sequences of herbicides with different modes of action to delay resistance
  • Be aware that although the use of higher resistance risk herbicides with lower-risk modes of action will help reduce weed populations, this will not prevent further selection for resistance
  • Follow the manufacturer’s recommendations on the label (e.g. for optimum dose and spray timing/application)
  • Take note of label restrictions – introduced to reduce risk of herbicide resistance – on the sequential use of both ACCase-inhibiting and ALS-inhibiting herbicides
  • Avoid treating if heavy rain is forecast, in waterlogged or frosty conditions, or if crop is suffering nutrient stress
  • Note that resistance can vary considerably between and, to a lesser extent, within different fields
  • Closely monitor herbicide performance to guide management
  • Conduct regular – at least once every two to three years – resistance tests on seeds or plants

Regular monitoring will help provide a strong indication of the unique resistance profiles present across a field.

It is much cheaper to stop resistance developing, so spotting the early signs is vital.

Herbicide resistance risk factors

Agronomic factor

Lowest risk

Highest risk

Cropping system

Good rotation of spring and autumn crops

Continuous winter cereals

Cultivation system

Annual ploughing

Continuous non-ploughing

Control method

Cultural only

Herbicides only

Herbicide use throughout the rotation

Different modes of action

Single mode of action

Weed infestation level

Low

High

Resistance incidence

None in vicinity

Identified locally (especially in similar cropping systems)

Arable weed management home


Some weed species associated with herbicide resistance in the UK
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