When is the Best Time to Spray Sunflowers for Head Rot?

With the registration of fungicides for sclertotinia head rot control in sunflowers, growers have an excellent management tool for reducing the impact of an economically devastating disease.

As the products and use is new to many growers, there are a number of question on timing.

  • Sunflower staging : Target the R5.1 to R5.2 stage (10-20% disk flowers open)
  • Field staging: 50-80% of heads at R5.1 to R5.2
  • Number of applications: Depends of product. If registered and conditions good for infection a second application can be made 12-14 days after the first application


Expert advice from Dr. Khalid Rashid, Pathologist with AAFC Morden, who has tested the head rot fungicides and sunflower staging timing for over 10 years is that:

“The growth stage of R5.1-R5.2, until end of flowering( 3 weeks window) is the most susceptible stage.  The main factors for susceptibility are the availability of ascospores from mushroom production in adjacent fields (less are produced in the sunflower fields), and there is humidity in the air and on the sunflower heads, for ascospores to germinate and infect the heads.    Sometimes, a second application 2 weeks after the first application may further reduce the disease infections.   In some years/some fields get high late infection after the end of flowering due to a flux of ascospores production late in the season coupled with favourable humidity/rain conditions.”

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Plan Ahead to Reduce Head Rot in Sunflowers

Prepared by Anastasia Kubinec, MAFRI Oilseed Crop Specialist

Sclerotinia Head Rot in sunflowers costs growers money.  It will reduce yields due to small and diseased seeds as well as seeds falling on the ground before the combine can pick them up.  It also reduces the quality of the saleable product leading to price reductions at the delivery point.

Fungicides are registered for the suppression of Head Rot in sunflowers just like products are available for suppressing sclerotinia in canola.

Application timing is R5.1 with a second application 7 to 14 days after the first application if environmental conditions and pressure remains high.  

See in pictures sunflower stages at: http://www.canadasunflower.com/wp-content/uploads/2012/11/Growth-Stages.pdf

With the weather lately being more conducive to the development of sclerotinia, you may want to speak with your retail the availability of a fungicide for your cropping needs.  The fungicide products that are registered for use in sunflower to control Sclerotinia Head Rot are the same ones registered for use in canola, pulses and other crops.

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