The Agriculture and Horticulture Development Board (AHDB) has developed a sclerotinia risk alerts tool for oilseed rape crops, that has been accurately identifying risk periods during the main flowering season in the UK.

The tool, which analyses forecasted and observed weather data, flags potential risk periods for the sclerotinia disease, and has been consistently delivering a high rate of accuracy, according to the AHDB.

Taking into account temperature and relative humidity as well as the weather patterns, the tool can provide an area forecast of how favourable conditions are for infection over the coming 48 hours.

A traffic light, map view is also provided by the tool to highlight which sites are at 'low- risk', 'near miss' or 'high risk' of infection.

Catherine Harries, who manages disease research at AHDB, said:

"After several seasons, it is reassuring that post-season analyses show the infection-risk forecast gets it right most of the time.

"E.g., the forecast alerts were highly accurate (92%) in 2021, when compared to actual alerts during the period March 15 to June 23 2021.

"However, accuracy was down on the 2020 results, mainly due to the wet May."

In 2021, the service accurately predicted that conditions were unconducive for sclerotinia infection for around 80% of the time, with conditions conducive for around 10% of the time.

According to the AHDB, relative humidity (RH) is challenging to predict accurately in comparison to temperature. The UK experienced the fourth wettest May on record in 2021 which contributed to higher levels of RH than predicted.

The board said that this may account for a lower level of accuracy in 2021 than in 2020, although there was still only 5% of false negatives generated that year.

Harries added: “Although forecasts are unlikely to ever be 100% accurate, they can guide activity on the ground."

Sclerotinia infections

According to the AHDB, the sclerotinia infection in oilseed rape is caused by the fungal pathogen sclerotinia sclerotiorum. 

The infection occurs if three main factors are in place: The presence of sclerotinia inoculum, warm and humid weather conditions and crops in flower.

The AHDB said that at growth stages 60-69, when crops are in flower, spores can be detected, either through the spore trap network or local petal tests. If these spores are detected and the forecast is showing high-risk infection conditions over the next 48 hours, then farmers should consider using a protectant spray.

The board says the optimum time for a single spray is just before mid-flowering on the main raceme and, since fungicides have protectant activity, should be applied prior to an infection risk alert.