Diseases of Oilseed Crops - Sunflower

Downy Mildew
Plasmopara halstedii

What to look for?
The disease shows up as odd appearing distorted plants at any stage of growth. Some plants may be severely stunted with normal heads that are devoid of seeds. Infected heads remain upright instead of downturning as with seed filled heads. Heavy infection usually occurs only in the wetter areas of the field.

Photo: Huang

Picture description Distorted infected plant.

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Management strategy
Resistant hybrid, seed treatments to control the seed-borne phase and avoidance of low lying wet areas.

Verticillium Wilt
Verticillium dahliae

What to look for?
First symptoms are stunting of plants and mottling of leaves. Formerly a major disease but now under control from resistant cultivars.

Photo: Huang

Picture description Unthrifty wilted sunflower plant.

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Management strategy
This systemic fungus produces microsclerotia that can persist in the soil for up to 5 years.Crop rotation and good weed control of host broad-leaved weeds will help especially with the more susceptible confectionary types.

Sclerotinia Wilt
Sclerotinia sclerotiorum Head infection

What to look for?
This disease is the limiting factor in sunflower production in Alberta. Sclerotinia can attack all parts and all stages of the crop from seedlings to mature heads. Even under relatively dry conditions, sclerotia at the soil surface or a few inches down can germinate and produce mycelium which infect the roots directly, moving from plant to plant. Under wet humid conditions sclerotia germinate to form apothecia. Conidiospores from these apothecia may infect and completely rot the sunflower heads.

Photo: Huang	Picture description Wilted plants.	Photo: Evans	Picture description Below ground infection--sclerotinia root rot.
Photo: Evans	Picture description Wilted plant.

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Management strategy
Consequently sunflower crops may only be grown in the drier parts of Alberta and then only once every five years and avoid sclerotinia-susceptible crops in the rotation.

Sclerotinia Head Rot
Sclerotinia sclerotiorum

What to look for?
Fully rotted head--many odd shaped black sclerotia replace the seeds. Infected stems and roots also produce considerable sclerotia that are returned to the soil in the crop residue.

Photo: Evans

Picture description

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Management strategy
None

Botrytis Head Rot
Botrytis cinerea

What to look for?
Botrytis head rot is a problem in very wet fields that hold up normal harvest times. The backs of the sunflower heads may rot and considerably damage the health seed.

Photo: Huang

Picture description Rotted seed head.

Management strategy
None at present other than the avoidance of fields prone to flooding.

Bacterial Leaf Spot
Pseudomonas syringae

What to look for?
An occasional disease of sunflowers in wet seasons.

Photo: Evans

Picture description Pseudomonas infected leaf showing necrotic areas.

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Management strategy
None

Other Diseases of Sunflowers

Phialophora Yellows - Found only in Manitoba on poorly drained soils.
Black Stem - Black spots on stems and leaves. Not usually a yield loss problem.
Powdery Mildew - Of little consequence.
Alternaria Leaf Spot - Generally confined to lower leaves.
Rust - Very common but yield loss is minimal. All stages occur on sunflowers.

Photographs and information assembled and prepared for ARD by Dr. Ieaun R. Evans Agri-Trend Agrology Ltd.

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