By Quinton Cubbon, AAg, Crops Extension Specialist, North Battleford
January 2024
Sclerotinia Stem Rot, or white mould, is caused by a soil borne fungus Sclerotinia sclerotiorum and is a disease that producers deal with in their canola fields. Every year, the Ministry of Agriculture conducts provincewide surveys on canola. In 2023, 217 sites were surveyed for sclerotinia to generate incident maps that are used by producers and agronomists to see problematic areas during the growing season. All the survey data is then analyzed to create the incidence maps. From all the surveys conducted, sclerotinia was observed in 30 per cent of the crops surveyed.
This year’s map showed sclerotinia severity is lower than 2022, with a few hot spots scattered across the north of the province around Meadow Lake, Prince Albert, Yorkton and in a couple small areas in Rural Municipality 253 and 162. In these areas, the incidence ranged from 20 to 40 per cent. The reason for these hot spots is linked with wetter conditions and spotty rains. Producers in these areas should be more aware of sclerotinia for the upcoming season. In 2023, drought conditions meant less sclerotinia incidence at zero to 10 per cent across the province. Please refer to the sclerotinia incidence map to view survey results for your area.
For the 2024 growing season, be on the lookout for sclerotinia as it can survive over winter at the soil surface and in stubble. Rainfall in the growing season can contribute to creating a dense canopy, which creates small microclimates where the disease can thrive. Heavy rainfall may be a contributing factor when it comes to increased incidence as the rainfall promotes the growth of apothecia. These apothecia are small mushroom-like structures that create the ascospores that germinate on the petals. Common symptomology of the disease is soft water-soaked rings that are white to grey in colour. Later symptoms you may see bleached plants that have a hollow stalk. Inside the stalk there will be black fungal bodies that resemble mouse droppings. Once the symptoms arise for sclerotinia, it is already too late to control the infection, but a fungicide may be used to help any further damage.
Control Methods
It is important to identify apothecia before determining whether a fungicide should be applied. This is why it is important to scout a field before a decision is made to spray or not. Areas within the map that have higher incidence should be on the lookout for sclerotinia, but that doesn’t mean if you had low incidence that the disease will not be a concern. Sclerotinia is weather dependent and needs moisture and humid conditions to thrive. If the 2024 season brings more rain, you can be sure that sclerotinia incidence and severity will increase.
If sclerotinia incidence is suspected to be high, a fungicide may be applied; although already infected branches won’t be protected, it will protect the branches that aren’t infected. Using a fungicide can also help reduce dockage by reducing shrivelled seeds caused by the sclerotia. Ideally, the best time to spray would be when the crop is as yellow as possible, around 30 per cent bloom. Some active ingredients that are registered for sclerotinia control are azoystrobin, flupyroxad, pyraclostrobin, fluoxastrobin and pydiflumetofen, just to name a few. It’s important to rotate registered products and groups to avoid fungicide resistance. For registered products to suppress sclerotinia, refer to the crop protection guide.
If you have any questions about the survey or sclerotinia, please contact your local crops extension specialists or call the Agriculture Knowledge Centre at 1-866-457-2377.