How to manage weeds in arable rotations – a guide

Weed control is vital for high yields of good-quality arable crops and to help manage the spread of pests and diseases. Yet, with limited active ingredients, a need to protect water and manage herbicide resistance, the weed challenge must be managed across the rotation.

Weed control has always been challenging but has become even more difficult because:

• Herbicide availability has declined
• Herbicide resistance is increasing
• Few new modes of herbicide action enter the market
• Herbicides are being found in water (threatening their registration for use)

Improved weed management requires us to:

• Get the most out of cultural control
• Minimise the use of herbicides
• Maximise herbicide performance, when applied
• Keep weed populations low
• Plan weed control across the full rotation

Inevitably, this requires an increased adoption of integrated pest management (IPM). For weed control, the challenge is to integrate crop choice/rotation, drilling date, cultivation method, herbicide use, resistance management and environmental protection.

Soil contains many weed seeds – this is called the ‘seedbank’. For optimum management, it is important to know the weed species present, as well as their abundance, status (e.g. herbicide resistance and dormancy) and distribution in the soil profile.

To make the most out of control options (non-chemical and chemical), it is essential to understand target weed populations. This will help you identify any chinks in their armour. The encyclopaedia of arable weeds is the definitive guide to arable weeds. For each weed, the guidance includes information on its life cycle, distribution and management. If known, the herbicide resistance status is provided.

The interaction between weed and crop growth is important, with most problems occurring when emergence coincides. Knowing when weeds are most likely to germinate will help you pinpoint control.

The interval between harvesting one crop and drilling the next is important, as a non-selective herbicide can be used on emerged weeds. Learn about drilling tactics to help you establish integrated weed management strategies.

The composition and sequence of arable crops in the rotation influences the weeds present and the opportunities for control. Discover which species are the most competitive to help you plan integrated weed management strategies.

Cultivations stir the weed seedbank, burying freshly shed seed and bringing seed from lower down the profile to the surface. The extent of this mixing is heavily influenced by the cultivation approach.

Herbicides form a large part, typically 20–30%, of the variable costs associated with producing a crop. With the need to consider herbicide-resistance risks too, it is important to target each spray required.

Find out how to optimise herbicide application techniques to make every drop count in the fight against arable weeds. This page covers spray equipment (e.g. nozzles) and rates.

Although product labels and technical support provide guidance on how to optimise herbicide effectiveness in specific situations, these general principles apply to all crops.

Find out about the causes of herbicide resistance and how to detect it in the field. Learn about the main UK weed species affected and how to manage resistance risks.

It is important to keep pesticides out of watercourses. Water quality legislation may affect or restrict use of several herbicides, particularly those used extensively, as well as those used at high rates and applied at times of year when drains may be running or there is potential for run-off to watercourses. The result of new legislation could be restrictions on rate and/or timing, with product withdrawal as a last resort. The Voluntary Initiative provides best-practice guidance for the main pesticides that pose a particular concern to water.