Flowering sprays – the last opportunity to prevent light leaf spot infections spreading onto oilseed rape pods and protecting against sclerotinia – need careful assessment during flowering to get the best results.

Three-quarters of samples assessed in March as part of Bayer’s SpotCheck initiative (now closed) were infected with light leaf spot – a slight increase of 3% from February’s results.

Not surprisingly, more light leaf spot was found in samples where no previous fungicide had been applied, said Adam Tidswell, commercial technical manager for Bayer in Yorkshire. In his area, 84% of samples had come back positive for the disease.

“If you haven’t protected against light leaf spot already, it makes it even more important to making sure your flowering spray also has light leaf spot as well as sclerotinia activity.

"Infection of the stem with light leaf spot results in small brownish, purple lesions often with black speckling around the edge,” he pointed out. “As the stems start to extend in spring, the lesions expand. In severe cases, stems split vertically along the lesion and occasionally break – this can allow access to other pathogens such as botrytis grey mould and sclerotinia.”

Severe pod infection can lead to premature ripening and seed shedding so it’s important to check for infection and apply a fungicide with both light leaf spot and sclerotinia activity, such as Proline (prothioconazole), before it causes other issues, he argued.

However, growers should be careful to monitor the crop’s growth stage. Philip Walker, arable plant pathologist at ADAS, said: “One of the things that makes light leaf spot such a challenging disease to control is that it can develop rapidly. You can go from first signs of infection to 100% disease incidence within a couple of weeks if the epidemic is severe.

“If the weather is conducive, light leaf spot continues to cycle which is why it’s important to protect your leaf layers with a fungicide at the flowering stage, as it is the last opportunity to prevent further movement up the canopy and onto the pods where it can cause the most damage via early senescence and pod shatter.”