ALMOST three-quarters of samples assessed in Bayer’s SpotCheck initiative for light leaf spot in oilseed rape were found to be infected with the disease during February.

This free leaf-testing service found varying levels of disease across the country, with the highest level of disease – 84% of plants infected by light leaf spot three days after incubation – in Herefordshire.

Eight samples were sent in from farms in Scotland – with all having been previously treated with fungicide. Despite this, all bar two were showing light leaf spot symptoms after ADAS testing, mirroring the three-quarters of positive samples from the UK as a whole. Four of the samples were showing more than 20% infection, with two August-drilled crops at more than 40% infection.

The high incidence of light leaf spot appearing in crops is likely a result of autumn spray activity coming to an end, said Gareth Bubb, a commercial technical manager at Bayer. He added that while many of these crops appeared disease-free in the field, they demonstrated clear light leaf spot symptoms after incubation.

“In Herefordshire, we are receiving a lot of reports of light leaf spot in crops, where autumn sprays are running out of steam. My advice would be to apply a fungicide with light leaf spot activity as soon as possible, such as Proline (prothioconazole),” said Mr Bubb.

“For those considering delaying spraying until green bud, I would urge them to consider going now with a light leaf spot fungicide, using PGRs where needed, and then delaying the green bud spray until yellow bud to provide some early control against sclerotinia.”

Philip Walker, an arable plant pathologist at ADAS, explained that the high level of light leaf spot was partially a result of the unseasonably warm weather experienced across the UK during February – including the warmest day in February on record.

“We usually see an increase in the levels of light leaf spot as temperatures rise in early spring. The time period from infection to visible lesions shortens under higher temperatures and the latent period is approximately 15 days at 12-15°C.

“The unseasonably warm temperatures experienced at the end of February would have contributed to the rapid development of light leaf spot symptoms. At early stem extension, infection levels of 15% plants affected cause an estimated 5% yield loss.

“As a result, it is vital to walk fields, check crops for light leaf spot symptoms and utilise services like the SpotCheck initiative to help with identification and confirmation of the disease,” pointed out .