Forty-five per cent of oilseed rape leaf samples assessed by Bayer’s SpotCheck initiative between January 4-11 showed light leaf spot symptoms, which it says demonstrated that the main disease epidemic had begun.
The SpotCheck initiative, a free oilseed rape leaf-testing service in the UK, found varying levels of disease across the country, with the highest level of disease – 47 per cent of plants affected by light leaf spot three days after incubation – in Northamptonshire, says Bayer.
The mild winter weather this season to date has been favourable for latent light leaf spot infection to develop into visible leaf symptoms, it adds.
Philip Walker, arable plant pathologist at ADAS, says: “The time period from initial infection to visible lesions is quicker when temperatures are higher. The average UK temperature in December was 6degC, so it would take approximately 30 days for an infection occurring in mid-December to be visible now.”
Ben Giles, commercial technical manager at Bayer, says that now light leaf spot incidence has risen, growers should take this opportunity to plan fungicide programmes.
“For crops yet to receive a fungicide with activity against light leaf spot then, especially if light leaf spot symptoms are present, the current good ground conditions could allow a spray application, such as around 0.4-0.5l/ha of Proline (prothioconazole). If growers applied a robust fungicide with light leaf spot activity in the autumn, then crops should still be protected at this stage of the season, especially if it went on from mid-November onwards.
“However, because light leaf spot symptoms can be difficult to identify, this is a key time to vigilantly walk and examine crops as regularly as possible. I’d also recommend utilising the SpotCheck service to know for sure which diseases are present in your oilseed rape.”
Mr Giles adds: “While it might be tempting to leave oilseed rape fungicides until stem extension/early flowering, this is a dangerous game if light leaf spot is already in the crop as this timing is at least eight weeks away, and growers may be better served to knock-down disease inoculum now to achieve the most effective control, rather than risk waiting.”
For information on Bayer’s free SpotCheck initiative visit: www.cropscience.bayer.co.uk/spotcheck