Rhizopus (Head Rot)
Rhizopus on back of sunflower

There are several headrots other than Sclerotinia that affect sunflower.  These are found primarily in the High Plains. Rhizopus is the most common.  The infected head turns brown and mushy. Once the head dries up it becomes hard and brittle.

rhizopus damage
Dry and brittle head
Life Cycle: The fungus enters the head through wounds produced by hail, birds or insects.  In wet and hot weather the infection spreads throughout the head.

Damage: Losses can be significant and some fields have been reported to be totally infected.  In NSA field surveys, Kansas fields had a high incidence of 20% in 2007 compared to 5% in 2006 and 1.5% in 2005.  Other states reporting damage of 5% or more in one or more of the survey years are Texas and Colorado.  The 2007 damage in Kansas may likely be associated with extremely high sunflower moth incidence.

Economic Thresholds: This is not well defined since there is not a fungicide treatment available.

Scouting Method: Not available    

Management: There is no fungicide treatment available for this fungus.  Good head insect control such as the sunflower moth is believed to be the primary management factor of the disease. 

Research: Very limited work has been done on the other headrots. 

Photos: Visit the Photo Gallery.

Another resource about Diseases can be found in the Archive section of The Sunflower magazine.

Source:  NDSU Extension Bulletin 25 Sunflower Production Handbook, NDSU Extension Service, September 2007 and High Plains Production Handbook June 2005

Additional Resources
High Plains Sunflower Production Handbook  file size: 1554 kb

NDSU Extension Bulletin 25 - Revised 9/2007 file size: 5591 kb

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