Light leaf spot (LLS) risk has remained relatively low, according to AHDB’s spring update for 2018/2019. The disease affects oilseed rape and is most prevalent in northern England and in Scotland.

Each spring, the autumn forecast is updated to take account of winter rainfall. As January and February were relatively dry, and because December was not particularly wet, the overall risk has reduced.

The regional forecast highlights the proportion of the winter oilseed rape (OSR) crop, and with a disease resistance rating of five, it’s predicted that more than 25% of plants will be affected by spring. However, the forecast does not show total incidence.

“Light leaf spot symptoms have already been observed at some monitoring sites. Although it is a relatively low-risk year, a high incidence can still occur in some crops,” said Jon West, who manages the forecast at Rothamsted Research.

“February got off to a cold start and this favours disease development. This was followed by unusually dry, sunny weather towards the end of the month, and this favours symptom expression. As there is always a lot of field-to-field and within-field variability, we advise vigilance and frequent crop inspections to assess LLS severity.”

Risk forecast

It is the first season since 2013/2014 that no regions have fallen into the highest risk category (>60%).

Towards southern Britain, especially in East Anglia, the risk forecast is exceptionally low, predicting even lower disease pressures than the relatively low-risk 2013/2014 season.

Historically, LLS risk is more serious towards the north of England and in Scotland. The 2018/2019 forecast in these regions can be described as moderate. The highest risk is predicted for the west midlands and Wales.