AHDB's improved light leaf spot forecast now reacts to rainfall during the winter, helping to focus crop monitoring in regions with higher predicted disease risk.
High winter rainfall encourages the development and spread of light leaf spot in infected oilseed rape, even at temperatures lower than required for crop growth.
If long-term average levels of winter rainfall are assumed, the 2021/22 forecast suggests that disease incidence will be highest in the South West and towards the north of the UK.
The forecast highlights the proportion of susceptible fungicide untreated oilseed rape crops predicted to have more than 25% of plants affected by the spring.
Robert Saville, who manages disease research at AHDB said: “As soon as the disease is observed, it is important to consider treating susceptible crops – with priority given to those sown relatively early.
“Since light leaf spot often occurs in distinct patches, whole-field monitoring is required to assess disease severity," he explained.
"Incubation of potentially infected leaf samples can help bring out symptoms – and some disease has already been detected this autumn, using this method.”
Recent industry consultations confirmed the forecast is valued, but one criticism was that the final forecast came too late to make a difference.
"As a result, we have replaced the static spring forecast with a live and dynamic winter forecast," Mr Saville added.
"Put simply, if the winter looks like it is going to be wetter than average at any given site, the risk will increase – and vice versa.”
The improved tool also features a scenario-planning function to help reveal the impact of a relatively wet and a relatively dry winter on the predicted disease incidence.
It now also exploits weather data gathered at hundreds of UK sites. Issued earlier this year, an improved phoma leaf spot forecast uses similar site-specific weather data.
