WITH some mild weather shoving crops forward at quite a rate, growers have been warned to keep an eye out for light leaf spot (LLS) infection in oilseed rape crops.

ADAS' plant pathologist, Julie Smith, said that a New Year trip to three Yorkshire sites found visible symptoms at two of them and the third revealed the disease after incubation tests were undertaken.

While this was quite a way south, farmers in the Borders have been experiencing similar conditions and should be alert to an outbreaks.

“Disease incidence is currently in the region of 10% plants affected and increases to more than 20% when plants are incubated. We saw first symptoms in one of our Herefordshire monitor fields recently," she pointed out.

"Light leaf spot can increase quickly and last year we saw the number of plants affected go from zero to 40% in two weeks, in a susceptible variety."

The delayed signs of infection are a slight mystery as, despite the perceived dry autumn, there were sufficient rain events to see phoma thresholds reached in mid-October in some parts.

Her advice now is to be alert. “From the first sign of LLS infection it can take off quickly and there’s little chance of eradicating it. Further sprays will only stop new infection,” she added.

She voiced concerns about phoma. With many crops only having had a single autumn treatment, she has seen some untreated plots with more than 70% plants affected.

Bayer’s Tim Nicholson pointed out that in many areas the good autumn has seen good growth and that plants should grow away from phoma, but warned the picture is very mixed.

He also advised checking for LLS and said disease data from Bayer's Thorney trials site had evidence of the value of an application ahead of stem extension last year.

“Treated plots had a November application of Proline275 (prothioconazole) and a second application was then made in early February. Controlling LLS led to a 50% or more increase in biomass by mid-March,” he said.

“I think if crops are showing signs of disease my advice would be to treat if travel conditions allow. There’s no guarantee that the conditions will be better at stem extension and it might be too late if either disease gets established,” he concluded.