Sclerotinia infection risk alerts (forecast) for oilseed rape

Sclerotinia stem rot is usually the main disease to consider during the flowering stages of oilseed rape. Although the infection cycle of the pathogen is complex, a good understanding of the three main risk factors – the presence of spores, warm and humid weather, and crops in flower – will help you target control.

This interactive dashboard highlights when conditions are conducive for infection at over one hundred locations.

The dashboard updates daily during March, April, May and June to cover the main oilseed rape flowering periods across the UK.

Outside of these months, the tool shows a single-date snapshot from the previous season to illustrate how it works.

Currently, the single-date snapshot is 15 April 2026, as this day showed all three risk conditions.

About the sclerotinia infection risk alerts

Weather and infection risk

If spores are present, conducive weather is required for infection to occur.

Based on observed weather for the past 24 hours and forecast weather for the next 72 hours, the interactive maps track the period of time that relative humidity (RH) and air temperatures are at or above threshold, 80% and 7°C, respectively.

If these thresholds are exceeded for 23 continuous hours, which is the time needed for sclerotinia to infect the crop, a weather-based infection alert is issued at the corresponding site, indicated by the dark blue circles. Near misses are also highlighted, indicated by light blue circles. Where infection risk is low, it is indicated by green circles.

Click on a circle to show an hour-by-hour chart of the sclerotinia infection risk for that site.

Sclerotinia control products are protectants and should be applied prior to infection, which is before the circles turn blue.

Forecast forensics

Our weather-based sclerotinia infection risk alerts support decisions. When thresholds for temperature and humidity are met, a risk-alert is triggered. However, forecast weather data is not always accurate.

Here we analyse how good the predictions were during the 2021 season, in relation to risk alerts.

The 2021 risk period was relatively cool, which delayed flowering and extended the flowering period. It also resulted in a relatively low number of weather-based infection risk alerts and, generally, low spore levels.

Our analysis shows that forecast alerts were 91.5% accurate (Table 1), when compared to actual weather during the period 15 March to 23 June 2021.

Differences tend to be due to relative humidity, which is harder to forecast, due to localised showers and local factors, rather than temperature, and this is particularly true in costal locations.

Table 1. Accuracy and classification of forecasted vs observed alerts

Correct alerts (91.5%)	Forecast days with alert	Forecast days without alert
Observed days with alert	1,336 true positives	724 false negatives
Observed days without alert	464 false postives	11,000 true negatives

Further information

Fungicide performance results for oilseed rape

Sclerotinia stem rot in oilseed rape

Complete guide to oilseed rape growth stages

Learn about the research behind the sclerotinia risk alerts

How to use the alerts video

Video notes:

Spore data is no longer published as part of the alerts service
The colours used to indicate infection-risk status have changed since the video was published

Topics:

Oilseed Rape Diseases

Sectors:

Cereals & Oilseeds