THOUGH the risk to oilseed rape crops from light leaf spot is said to be ‘low’ this autumn, growers are still being advised to be vigilant.

With the north of England and Scotland said to be at ‘moderate’ risk in the AHDB Cereals’ most up to date risk assessment, the threat is great in those areas than it is elsewhere.

The regional forecasts highlight the proportion of WOSR crops (with a disease resistance rating of 5) predicted to have more than 25% of plants affected by the disease in the spring. It is the first season since 2013/14 that no regions have fallen into the highest risk category (greater than 60%).

For southern England, the risk is exceptionally low, with the forecast predicting even lower disease pressures than the relatively low-risk 2013/14 season.

Historically, though, LLS risk is more serious towards the north of England and in Scotland but the 2018/19 preliminary risk in these regions is being put at ‘moderate’.

Dr Neal Evans, plant pathologist at CropSave, who put together the forecast, said: “Disease survey data from commercial crops showed a relatively high pod incidence for LLS this year. Although the potential for higher disease pressure was there, relatively warm temperatures have helped peg back risk across Britain.”

The forecast can be used to guide crop management decisions. For a more accurate picture of local risk, people can build a customised forecast via the AHDB website. This forecast also takes account of variety, sowing date and autumn fungicide applications.

As local risk varies, the forecasts should only be used as a guide and crops should be inspected regularly on a field-by-field basis. To provide the strongest risk assessment, plant samples should be put in polythene bags and kept at 10-15°C for around five days to bring out symptoms.

The preliminary forecast uses previous season pod incidence data, deviation from 30-year mean summer temperature data and 30-year mean rainfall data. In spring, the forecast is updated to reflect deviation in actual winter rainfall data from the 30-year mean.

For further information on LLS, fungicide performance and resistance management, visit The page also hosts a recently updated phoma leaf spot forecast.