Is your Oilseed Rape Ready for Winter?

Winter can be a challenging season across the agricultural sector, particularly for those growing oilseed rape (OSR). Therefore, it is essential to prepare your crops to help deliver optimal yields and good health come the spring. If you are wondering whether your OSR is ready for winter, we have outlined seven key steps to help maximise your crop’s success.

1. Check the growth stage

Before the onset of wet winter weather conditions, your OSR should ideally be at the 4-6 leaf stage.

This leaf stage is characterised by:

  1. General appearance: The plant will look like a small rosette with leaves layered in a spiral pattern. The leaves should be dark green, and the overall plant size can be a few inches in diameter, depending on the specific variety and growing conditions.
  2. Stem: The main stem remains relatively short during this stage and may have a purplish tint, especially in colder conditions.
  3. Leaves:
  • The first ‘leaves’, known as cotyledons, appear after the seed germinates and are generally round and broader than true leaves.
  • You will see the true leaves starting to appear from the top of the stem. These are typically more elongated compared with the round cotyledons. By the 4-6 leaf stage, you should be able to count four, five, or six of these true leaves, starting to overlap each other.

If plants have reached the 4-6 leaf stage they will have developed a strong enough root system to withstand the challenges winter can present, from cold snaps to pests.

If your crop is not at this stage by late autumn, consider some protective measures, such as a foliar-applied nutrition spray to boost its resilience.

2. Examine the Green Area Index (GAI)

GAI is a measure of the green leaf area per square metre of ground.

You can examine the GAI of OSR through direct measurement:

  • Leaf collection: At several locations within the field, randomly select plants and remove all their leaves. Ideally, you should sample from various places to account for variability.
  • Leaf area measurement: Measure the total leaf area of the collected leaves using a leaf area meter.
  • Calculation: Divide the measured total leaf area by the ground area from which the plants were sampled to get the GAI.

A healthy pre-winter OSR crop should have a GAI of around 1.0 to 1.5. This indicates enough leaf cover to capture sunlight effectively, but not so much that the crop becomes vulnerable to frost damage or pests.

3. Assess soil nutrients

Well-nourished soil can help OSR plants survive the winter months.

Before winter, test your soil to ensure it has adequate levels of potassium (typically around 150-250 mg/kg) and magnesium (100-150 mg/kg).

These nutrients are vital for the crop’s winter hardiness and can prevent problems like leaf chlorosis. This typically shows symptoms of leaf yellowing, when it should normally be green.

Adjusting your fertiliser strategy following soil testing results is important for optimal crop health and reducing fertiliser wastage.

4. Pest and disease management

Pests, such as the Cabbage Stem Flea Beetle (CSFB), and diseases like Phoma Leaf Spot, can seriously impact OSR’s winter survivability.

Regularly inspect your crops for any signs of these threats and treat them accordingly.

A well-timed application of fungicide or insecticide can help prevent minor issues from becoming significant challenges and impacting the end yield of your crop.

5. Guard against lodging

Tall and spindly OSR crops are more susceptible to lodging (permanent falling over), particularly under the weight of snow or during high winds. While some lodging is normal, excessive lodging can lead to yield losses.

Ensure a balanced nutrient regime and consider plant growth regulators if your crops tend to grow too tall.

6. Choose winter-hardy varieties

If your region frequently experiences harsh winters and bad weather conditions, you might consider planting winter hardy OSR varieties such as Ballad and Flamingo, which have excellent vigour.

These are specifically bred to withstand cold temperatures and challenging conditions.

For further information about OSR varieties, contact your local seed supplier or agronomist to learn which variety is best suited to your land.

7. Proper drainage

Waterlogged fields can harm OSR plants, making them more susceptible to diseases and root rot.

Root rot is a common crop disease that affects the plant roots, causing them to decay. Once the roots are damaged, they can no longer absorb water and nutrients effectively, which often results in plant death if the condition is not addressed.

Before winter sets in, ensure your fields have adequate drainage to prevent water from pooling. This can be achieved by maintaining ditches, creating slight slopes, or installing drainage systems.


As seen in the top tips outlined above, preparing your oilseed rape for winter is all about vigilance, timely interventions and understanding the crop’s specific needs.

By following these steps and keeping a close eye on weather conditions, you can help ensure your OSR not only survives the winter, but yields optimally come spring.

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