Oilseed rape growers are being warned to watch out for signs of light leaf spot (LLS), as high levels of this common fungal disease have been found in UK crops.

LLS, which can potentially result in significant yield loss, thrives in cool, moist conditions meaning the recent wet weather has contributed to its prevalence.

Mark Bollebakker, a senior field trials manager at AHDB, said that while inspecting Recommended List (RL) trials in recent weeks, he has not seen such high levels of infection at some locations before: “Farmers should be wary of this outbreak as it could potentially have an impact on yields - unless carefully managed through the use of fungicides over the next couple of weeks.

The Scottish Farmer: Oilseed rape growers warned to look out for signs of light leaf spotOilseed rape growers warned to look out for signs of light leaf spot

“The spread of LLS has been particularly bad in areas of the country that have been particularly impacted by the poor conditions over the past few months. The symptoms can vary depending on the severity of the infection, in the early stages especially, and it can be a real challenge to spot. The biggest risk now is if the infection gets onto the pods, which can cause them to become brittle and thereby shed their seed prematurely before the harvest.”

LLS is caused by the fungus Pyrenopeziza brassicae and is characterised by small, light green or brown spots on the leaves of the plant, with a typical 'fag-ash' appearance.

AHDB senior crop production systems scientist Paul Gosling said it is vital that growers are wary of how easily this disease can spread: “The fungus overwinters on crop residue and can be spread quickly through rain splash and wind, as well as by contaminated machinery such as tractors sprayers. Once the fungus infects a plant, it can quickly spread throughout the entire crop if left untreated.

“In addition to causing significant, direct yield loss, light leaf spot can also weaken the plant, making it more susceptible to other diseases and pests. This can further impact crop health and yield, making it essential for growers to properly manage and control the spread of the disease.

“Regular monitoring of crops for early signs of infection is crucial for effective management of this disease. Where the disease is established, growers should consider using fungicides. These work by inhibiting the growth of the fungus and protecting the plant from further infection.”

Further guidance on selecting the appropriate products and rates can be found in AHDB’s Fungicide Dose Response Curves for Oilseed Rape report.