sclerotinia in stalk
Sclerotinia in stalk

Sclerotinia commonly called ‘white mold’ affects most broad leaf crops and weeds.  It can be a devastating disease and in sunflower it is highly dependent on weather conditions.  Sunflower can be affected in three ways:  1. Root infection which results in wilt or stalk rot; 2. Midstalk infection; and 3. Head infection or head rot.  The latter two infections are dependent on ascospore infection.

Disease Cycle: Sclerotia are hard small black bodies produced by the disease in a host of broad leaf crops.  Sclerotia over winter in the soil and exist in the soil for many years.  Wet soil conditions over a period of 10 to 14 days can stimulate the sclerotia to germinate creating tiny mushrooms.  These mushrooms produce apothecia or tiny spores which can be wind-blown to nearby fields.  The spores need dew or rain and dead or senescing plant tissue such as dead florets to germinate and infect.  Wet and cloudy conditions are necessary for the disease advancement.
The infection occurs via the sunflower roots which stimulate the nearby sclerotia to germinate.  The infection moves into the plant via the roots and the plant dies suddenly or literally wilts.  Sclerotia develop at the base of the diseased plant and return to the soil.
sclerotinia stalks
Damage to sunflower due to sclerotinia stalk rot

Damage: Wilt can occur in fields which have a history of broadleaf crops like canola, soybean, peas and sunflower where the disease has occurred in past years.  Crop surveys over the last five years in the Dakotas and Minnesota has found that about 1 out every 2 fields have some infection.  The average is about 3 percent of the crop is affected.  A diseased plant will not produce harvestable seed.  The infected plant will usually lodge well before harvest. See Wilt/Stalk Rot photos.

Management:  Rotation is a good management practice.  Following a heavy Sclerotinia infected crop with an early planted small grain crop the next spring under no-till can often reduce the sclerotia load in that field, according to research conducted in Wisconsin.  Intercept WG is a soil applied biologic product that can reduce the sclerotia soil load.  Sunflower hybrids are showing great advances in tolerance to stalk rot.  If you are planting sunflower in a suspected field, it will be important to find the most resistant hybrid. See the hybrid disease ratings.

Research:  Sclerotinia is being actively researched in sunflower and other broadleaf crops via the National Sclerotinia Initiative.  This competitive funding program directs about $2 million annually in various research programs around the country.  Sunflower researchers have been a key recipient of this funding.  Wild sunflower genes show considerable promise for additional resistance.  Public and private parent lines, experimental and finished hybrids are tested throughout ND and MN.  Sclerotinia infected millet seed is tilled into the soil at about the V-6 stage which usually provides good infection.  This provides a uniform system for rating material and hybrids.  Hybrid resistance is the best option to date to limit this disease.  Go to Yield Trials & Hybrid Disease Ratings for hybrid testing results.  There are no fungicides labeled for this disease.
sclerotinia head rot
Sclerotinia Head Rot
Of these two infections, head rot is by far the most serious.  Both mid-stalk head rot occur when ascospores settle on dead plant tissue.  For this to occur weather conditions have to be ideal as indicated in the disease cycle description above.  Ascospores can be windblown from neighboring fields.

Damage:  Under the right weather conditions this head rot can be devastating.  Not only can there be substantial yield loss but quality loss as well.  This is particularly true for confections.  The disease impacts only a small percentage of the crop each year. See Head Rot photos.

Management:  Since ascospores can be blown in from other areas, rotation is not a management technique.  Hybrid tolerance is the best management technique to date.  Again, refer to the disease rating trials. Under heavy infestation even a tolerant hybrid will have the disease.  But the percent of infection will be reduced considerably compared to the susceptible hybrids. 
misting fields
Sclerotinia Misting Site
Langdon, ND
:  A great deal of work is being done on this disease at the public and private level.  Five misting sites duplicating the required disease environment are being utilized for testing breeding lines and hybrids each year.  Ascospores are sprayed on the face of each sunflower plant insuring infection.  Resistant genes are being identified and transferred into breeding lines.  USDA has already provided a number of germplasm releases to the private sector.  There are multiple genes responsible for resistance so it is a matter of ‘building blocks’ to resistance.  Good progress is being made in this area.  Fungicide testing is ongoing as well.  There remain a number of unanswered questions before a fungicide can be labeled.

For further information, click on the link below. Another resource about diseases can be found in the Archive section of The Sunflower magazine.
Additional Resource
High Plains Sunflower Production Handbook  file size: 1554 kb

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

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