Sclerotinia stem rot: To spray or not to spray?

Sclerotinia stem rot: To spray or not to spray?

Sclerotinia stem rot is caused by the fungus Sclerotinia sclerotiorum. Sclerotinia stem rot is the most economically significant canola disease in Canada. In 2020, growers in Saskatchewan lost more than half a billion dollars in farm receipts to sclerotinia.

Sclerotinia has become more serious as canola production has increased, likely due to a combination of more acres of canola in rotations and management practices that contribute to high yielding, dense crop canopies that have a more conducive microclimate for disease development.

What you should look for     

Fungicides are the most effective management tool to control sclerotinia stem rot in canola when the risk of infection is high. The decision to apply a fungicide to prevent sclerotinia stem rot depends on the risk of the disease developing. This decision may become clearer by answering these four questions:

  • Have environmental conditions prior to flowering been wet enough for apothecia development and survival?
  • Is the canola crop canopy dense and is yield potential high?
  • Does the weather forecast predict precipitation and/or humidity during the flowering period?
  • Is the pathogen present in sufficient quantities?

If the answer is “yes” to all four of these questions, then spraying is generally recommended. If the answer to some of the questions is “no”, then the decision is more difficult. Utilize the Sclerotinia Stem Rot Checklist to help with the decision. When making the spray decision, take canola price and overall profit potential into consideration.

Here’s an example, provided by Clint Jurke, Agronomy Director, Canola Council of Canada, to calculate the economics of spraying for sclerotinia stem rot for 2021:

  • Cost of fungicide application: $25-$30/acre (chemicals plus machine cost).
  • If selling canola for $15/bu, then 2 bu/ac canola covers cost of fungicide.
  • If a grower has a 50 bu/ac crop coming, then 2 bu/ac works out to be 4% of that yield.
  • Sclerotinia robs yield on a 1 to 2 ratio – for every 2% infection, there is a 1 % yield loss. This means that 4% yield loss would be caused by 8% sclerotinia infection. 
  • The economic threshold in this example is 8%. This means at 8% infection or greater, a grower is justified to spray.

Canola canopies with yield potential of less than 30 bushels per acre are less likely to suffer from sclerotinia stem rot infection, so spraying may not be economical unless conditions for infection are ideal. Crops with an open canopy could be at lower risk, particularly if warm and windy weather allows them to dry out in the afternoons. However, if frequent rains and high humidity keep the plants wet, then there is still a threat of infection. Rainfall at flowering and thick canola canopies increase the sclerotinia risk, especially if the field is located in an area where sclerotinia sprays are often warranted.

These videos provide more information:
Sclerotinia spray decision
Sclerotinia fungicide timing

You need to invest in canola to maximize yields and profitability. It’s not a crop that you can look for opportunities to save costs because there are weeds, insect pests and diseases to deal with during the crop growing season. Crop protection is key to productivity.”

- Clint Jurke, CCC

Get important canola info delivered to your email. Join our mailing list