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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