Oilseed rape establishment and weed control in 2026

As we enter the main oilseed rape drilling window, we have nearly all the components for a successful crop, except one critical factor: moisture.

Key questions being asked this season include:

• When should we drill?
• How late can we drill?
• How much moisture is needed?
• And what can we do to support crops ahead of drilling?

With much of the UK experiencing exceptionally dry conditions, successful establishment will be determined far more by soil moisture availability than by calendar date. While many fields are cleared and ready to drill, sowing into dry seedbeds can lead to uneven germination, patchy emergence and reduced crop vigour, leaving plants more vulnerable to cabbage stem flea beetle, slugs and weed competition.

For successful establishment, oilseed rape requires moisture, light, nutrition, space and suitable temperatures to grow. Encouragingly, soil temperatures remain well above average across many regions, supporting rapid growth and extending the potential drilling window. In many situations, growers already have the space, light and temperature required.

Moisture, however, remains the limiting factor. An oilseed rape seed typically needs to absorb nearly half of its weight in water before germination can begin. Insufficient moisture may delay emergence and reduce vigour, but problems become far more serious if the radicle emerges and then moisture runs out, as plant survival is unlikely. Moisture is also essential for nutrient uptake and biomass production, so when assessing forecasts and drilling dates, it is important to ensure there is sufficient rainfall not only for germination but also for sustained growth to get crops up and away in the following weeks.

Although waiting for rain can be frustrating, experience continues to show that some of the highest-yielding crops are established later in the season, often well into mid-September, when conditions are favourable. Growers should therefore focus on drilling into adequate moisture rather than chasing early drilling dates.

Attention should instead be placed on the factors that can be controlled: selecting vigorous varieties, alleviating compaction, creating a firm seedbed with excellent seed-to-soil contact, placing seed at 2-3 cm depth, ensuring adequate nutrition and conserving as much moisture as possible.

In today's climate, a conditions-led approach to drilling is increasingly important. Patience, combined with the confidence to drill later when conditions are right, is often the key to achieving strong establishment and resilient, high-performing crops.  With soil temperatures currently remaining high and modern vigorous varieties establishing rapidly, crops can be drilled later into the season. Over recent seasons, crops drilled later into favourable conditions have frequently outperformed those drilled earlier into poorer, drier seedbeds.

Weed impact at establishment

Successful oilseed rape crops are built from the moment they emerge, making early weed control one of the most important decisions in protecting yield potential. Weeds emerging alongside the crop compete aggressively for moisture, nutrients, light and space, reducing plant vigour, slowing canopy development and increasing vulnerability to pests and disease. Minimising weed competition during this critical establishment phase helps crops root strongly, grow rapidly and make the most efficient use of available resources.

Early weed control is particularly important in oilseed rape because the crop is relatively uncompetitive during its establishment period. Removing weed pressure early gives plants the best opportunity to achieve rapid, even establishment and develop a robust canopy ahead of winter.

However, weed control decisions are often balanced against the uncertainties of establishment. As a result, many growers have moved away from traditional pre-emergence herbicide programmes and instead favour post-emergence approaches. This strategy allows crop establishment to be assessed before further investment is committed.

Once the crop is successfully established, controlling broad-leaved weeds in early autumn helps preserve crop vigour, reduces competition for key resources and avoids the need for later applications when wet weather and poor ground conditions can limit sprayer access.

By prioritising weed control during establishment, growers can maximise crop competitiveness, protect yield potential and improve the return on their investment in oilseed rape.

Hugh Guinan, Corteva Field Technical Manager, discusses the key factors behind successful oilseed rape establishment and why a condition-led approach could make all the difference.

Weed control

Weed pressure

Drilling date, establishment method and cultivation strategy all influence weed populations. The timing, depth and frequency of cultivations can affect both the composition and density of weed species present.

Where possible, start with a clean seedbed and target both grass weeds and broad-leaved weeds carried over from the previous crop.

In recent years, some growers have opted for earlier drilling to take advantage of warmer soil temperatures and available moisture. However, following the lack of moisture to date only a small proportion of the crop has been drilled in July, early August yet. The remainder is awaiting sufficient moisture to establish.  

When conditions favour oilseed rape establishment, they also favour weed germination. Regular crop monitoring is therefore essential to identify emerging weeds and apply treatments before they become difficult to control. Controlling weeds early is often more cost effective and beneficial to the crop.

Companion crops

Companion crops can play a valuable role in oilseed rape establishment, helping to suppress blackgrass while delivering wider agronomic benefits such as improved soil health, crop nutrition, pest management and support for beneficial insects. However, they should complement, not replace, a robust herbicide programme. Herbicide strategies should be tailored to the weed spectrum, companion crop species and intended lifespan within the crop.

For grassweed control, Kerb® Flo 500 offers flexibility through its selectivity to many commonly used companion crops, enabling effective blackgrass control without compromising the system. Companion crops can also support propyzamide stewardship by reducing soil runoff and active ingredient losses following heavy rainfall. Where additional broadleaf weed control or companion crop removal is required, products such as Astrokerb®, Belkar® LaDiva® and Korvetto® provide further management options. The key is to integrate companion crops and herbicides in a way that maximises crop establishment and weed control while supporting long-term stewardship objectives.

Belkar

Belkar® herbicide offers flexibility in both rate and timing, allowing growers to assess crop establishment before making weed control decisions. This post-emergence approach provides an alternative to higher-risk preventative strategies and enables applications to be tailored to individual field conditions.

The flexibility of Belkar gives growers and agronomists time to assess visible weed pressure, as well as any impact from cabbage stem flea beetle or slug activity.

Belkar provides control of a wide range of competitive broad-leaved weeds, including cleavers, cranesbill, poppy, fumitory, shepherd's purse and mayweed. For the full list of controlled weeds, click here.

Belkar can be applied from the two- to four-true-leaf stage as a single application, a sequence of applications, or as a later higher-rate treatment to suit crop development and weed pressure.

       Belkar application options

1. Early application at two true leaves, apply 0.25 L/ha to control weeds that have emerged alongside the crop. In some situations, this may provide sufficient broad-leaved weed control before a later application of Astrokerb (propyzamide + aminopyralid) or Kerb Flo 500 (propyzamide) where grass weed control is required.
2. Sequential application where weed pressure is high and a second flush of weeds emerges, a further application of 0.25 L/ha can be made, typically two to four weeks after the first spray.
3. Later application where workloads or conditions dictate, growers can wait until the crop has reached six true leaves and weeds have emerged before applying 0.5 L/ha after 15 September. This provides effective control of larger weeds heading into autumn.
4. Trials have demonstrated that earlier applications of Belkar, typically during September, not only improve weed control by targeting smaller weeds but also reduce competition during the critical establishment phase, helping crops achieve stronger growth before winter.

For earlier weed control

LaDiva herbicide combines Belkar with Aminopyralid into one product. LaDiva extends Belkar’s spectrum and lifts performance on larger weeds in earlier drilled or high-pressure situations. Both Belkar and LaDiva can be utilised once the crop has established and independently of soil moisture. LaDiva utilises aminopyralid earlier in the programme, removing difficult weeds before they impact the crop or become too large to control. It allows simplified timing of the propyzamide later in the season.  

Astrokerb and Kerb Flo 500

Propyzamide-based herbicides such as Astrokerb and Kerb Flo 500 remain important tools for the control of blackgrass and ryegrass in oilseed rape.

Propyzamide is a soil-active herbicide that binds to soil particles and, when applied to soils below 10°C, can remain active for up to three months.

The active ingredient forms a treated layer within the top 5 cm of soil, where it is absorbed by the roots of germinating grass weeds, ultimately leading to weed death.

For optimum performance, growers planning to use propyzamide should consider non-inversion or minimum-tillage systems. These approaches help keep grass weed seeds within the topsoil, ensuring they remain within the herbicide's zone of activity.

To get the best from propyzamide, we need to keep it where we need it, not only supporting stewardship and reducing the risk of it entering water, but also to increase efficacy in the field. Protecting the active in the field is key, ensuring it is applied at the correct dose, correct time and in the correct conditions.   Visit our propyzamide knowledge hub for more information.

Corteva is committed to supporting farmers and agronomists to grow oilseed rape successfully.

Our OSR online hub is your go-to resource throughout the season, offering timely updates and invaluable resources. Be sure to visit and bookmark this section of our website to stay informed and supported every step of the way.