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High prices make investing in oilseed rape crops worthwhile this spring – but variable growth means management must be tailored to individual fields.

• Good nutrition is key to success

• Manage canopy size if needed

• Keep careful eye on winter rape

High prices make investing in oilseed rape crops worthwhile this spring – but variable growth means management must be tailored to individual fields.

“A lot of winter oilseed rape seems to have escaped significant cabbage stem flea beetle damage this season,” says Mike Thornton, head of crop production for agronomy firm ProCam. “But pigeon damage in some fields has been awful.”

Crop sizes range from plants barely above the ground to those almost knee-high. Pigeon-damaged crops with decent root structures have a chance to recover. But Mr Thornton says it is important to ensure recovery is not hampered by lack of nutrients.

“Badly-affected crops may need extra nitrogen – particularly in the worst parts of fields,” he explains. “It will be important to avoid micronutrient deficiencies, especially boron and molybdenum.”

Flower buds

Preventing pigeons from grazing flower buds will be vital as the season develops, adds Mr Thornton. Winter oilseed rape that suffers delayed flowering due to pigeon damage can become badly infested by pollen beetles later, he warns.

Growers with crops that flower unevenly will find it hard to time sclerotinia fungicide sprays accurately. Canopy size in forward crops may need regulating as temperatures rise and days get longer. This reduces lodging and opens the canopy to let in light.

“If you’re also having to target light leaf spot or phoma infections, canopy management can be achieved at the same time using a treatment combining a suitable fungicide with a plant growth regulator. This will also help to even the crop up.”

Light leaf spot outbreaks appear sporadic – but have been reported in some areas. Even varieties with greater resistance can be affected – making it important to remain vigilant to ensure it can be controlled early.

To safeguard yield potential during flowering, Mr Thornton urges similar vigilance against sclerotinia, botrytis and alternaria infections. These are highly weather-dependant – but most fungicides work preventatively, so timeliness is key.

Club root

After the mild winter, another disease being reported this year is club root. Little can be done against it at this stage of the season – although applying a calcium carbonate dressing to raise soil pH is an option.

“It’s important to look after the crop nutritionally because nutrient uptake via the deformed roots of infected plants will be restricted. For the future, however, what you can do is note down fields that are affected.”

Mr Thornton says doing this helps with longer-term crop management, including rotation planning, liming of infected fields, choosing more tolerant varieties, and the delayed drilling of winter rape.

Once rape comes into flower, Mr Thornton says growers should guard against pollen beetle. Although normally less of a problem in winter rape than spring rape, crops that flower later are more susceptible.

“If treating pollen beetles, do so only according to pest thresholds – we need to use insecticides sparingly to protect against resistance.”