Oilseed rape growers warned to look out for signs of light leaf spot

Oilseed rape growers are warned to be vigilant for signs of light leaf spot (LLS). High levels of this common fungal disease, which can cause significant loss in yield, have been found in UK crops.

LLS thrives in cool, moist conditions, meaning recent wet weather has contributed to its prevalence.

Mark Bollebakker, Senior Field Trials Manager at AHDB, has inspected Recommended List (RL) trials over recent weeks. He observed that 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 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. The disease is characterised by small, light green or brown spots on the leaves of the plant – this gives them a “fag-ash” appearance.

Paul Gosling, Senior Crop Production Systems Scientist at AHDB, warned growers to be 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.”