Light leaf spot identified in oilseed rape crops from Scotland to Somerset

Bayer’s SpotCheck service has identified light leaf spot infections in oilseed rape crops across the length and breadth of the UK, indicating that growers should remain vigilant for disease onset this winter and consider a fungicide spray before Christmas.

Since the SpotCheck service re-opened for submissions in October, there has been an increasing number of leaf samples testing positive for light leaf spot. Samples of 30 leaves are sent in by growers or their agronomists to the SpotCheck team at ADAS, who incubate the leaves for three days at room temperature before assessing them for signs of disease.

By 9 November, 50 out of 102 samples revealed 10% incidence of light leaf spot or more, after three days of incubation. Of these, 19 samples showed 50% disease incidence or more.

Positive samples were received from a very wide geographic area, from Scotland and the north of England, to the East of England including Lincolnshire, Norfolk, Suffolk, Cambridgeshire and Kent, and further West from Somerset and Wiltshire.

Ella Crawford, Bayer Commercial Technical Manager says these early results confirm that light leaf spot is no longer just a problem for growers in the North.

She says: “These light leaf spot infections in early November in crops in East Anglia, the South Coast and the West is further evidence of the southerly march of this disease. All oilseed rape growers should be looking for signs of this disease when crop walking.

For Andrew Barr, who farms in central Kent, light leaf spot has historically not been an issue, but he has now realised it is a disease he needs to be aware of.

Part of his control strategy is to grow varieties with higher resistance ratings for light leaf spot, alongside regular crop walking by his agronomist who will also incubate leaf samples to hasten disease expression.

“The challenge for us is balancing investment in the crop in the autumn with expected returns. Our crops are looking much better this year but we will be watching for early signs of disease before spraying,” said Mr Barr.

The aim of funcigide applications in the winter is to protect the lower crop canopy, and prevent the disease spreading to the pods in the spring during stem extension. Fungicides only offer protectant activity, so timing sprays depends on catching the disease early.

“Where fungicides applications are being planned this side of Christmas, growers should consider using a product such as Proline which offers activity against light leaf spot as well as Phoma,” advises Ms Crawford.

Light leaf spot is difficult to identify in the field. The only visible signs of disease are small white dots scattered across the top or underside of the leaf. However, they may appear sporadically across the field, so are easily missed, and a hand lens is essential.

In East Lothian, Scotland, James Kennedy will be using the SpotCheck service to identify any light leaf spot incidence in his oilseed rape, and help him decide whether to include a fungicide with his propyzamide application this winter.

To use the SpotCheck service, growers should request a sample pack from ADAS Boxworth, collect 30-35 leaves from a single field in a ‘W’ pattern, complete the assessment form and send the leaves to ADAS. The results will be emailed within five working days.

For more on the SpotCheck initiative visit: cropscience.bayer.co.uk/spotcheck

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About The Author

John Swire - Deputy editor of Agronomist and Arable Farmer as well as responsibility for the Agronomist and Arable Farmer and Farm Business websites. After 17 years milking cows on the family farm John started writing about agriculture in 1998 and has since written for a variety of publications and has developed a wide circle of contacts within the industry. When not working John is a season ticket holder at Stoke City and also of late has become a fitness freak, listing cycling, swimming and walking as his exercises of choice.