Sclerotinia stem rot is cause by the fungus Sclerotinia sclerotiorum which affects many broad leaved crops in the field and protected crops.
In oilseed rape, severe attacks are uncommon and many crops are sprayed unnecessarily with fungicides at flowering.
Sclerotinia has a complex disease cycle, it is primarily soil-borne and the risk of problems relates to previous history of the disease and suitable weather conditions for spore production and infection.