Should You Apply a Fungicide for Sclerotinia in Canola


This spring’s challenging planting conditions has resulted in quite a few of uneven canola stands with both reduced  populations and delayed emergence. This has  some growers weighing the merits of applying a fungicide this season.  Sclerotinia incidence varies greatly between fields and years thus making routine spraying of fungicide unprofitable. However when the risk of sclerotinia is high, applying a preventative fungicide can reduce disease severity and significantly improve yield.  Assessing the risk and benefit of applying a fungicide can be a challenge, but it important to judge each field to decide on odds of an economic response.

Risk Factors

  • Dense crop canopy.
  • Wet weather leading up to early bloom– 25-50 mm (1-2 inches) of rain that saturates the soil in the two weeks prior to bloom.
  • Showery weather and high humidity is predicted for the  anticipated flowering period.  Sclerotinia needs two days of wet weather at flowering for spores to germinate. Optimum temperature for sclerotinia growth is 15 – 200 C.  Temperatures over 300 C (86 F) stop disease development.

Fungicides and Timing

There are a number of fungicides registered for sclerotinia control.  For the fungicide to be effective it must be applied as a preventative treatment, prior to any signs of mould growth. Fungicides provide about 10-14 days of protection.  

Optimum timing for application is when there are a maximum number of flowers open and before any petals fall to ensure petals are protected before infection occurs.

This is because flower petals that drop onto leaves and stems are the initial point of infection for sclerotinia. At the optimum stage for spraying (30% bloom) there are about 20 open flowers on the main stem, very few on secondary stems, and few pods.  If a field is vary uneven in flowering but warrants spraying,  time application for when the greatest percentage of canola plants are at the correct stage.


% Flowering Stage Number of Open Flowers on Main Stem Time from First Flower Days (approximate)
10 At least 10 2 – 4 days
20 14 – 16 5 – 6 days
30 At least 20 7 – 8 days
 For images of bloom stage, refer to the Bayer bloom guide posted on Ontario Canola Growers website at


20% Flower 14-16 Open/Dying Flowers
20% Flower 14-16 Open/Dying Flowers