Diseases of Oilseed Crops - Canola

Alternaria Black Spot
Alternaria brassicae (Gray Leaf Spot)

What to look for?
Distinct target spot lesions on the older leaves during wet, cold weather in July and early August. If the weather continues wet and cold the pod and stem spotting builds-up rapidly.

Photo: Evans	Picture description Lesions on pods and stems.	Photo: Evans	Picture description Club-shaped Alternaria spores.
Photo: Evans	Picture description Shattered pods caused by pod lesions - loss of yield can be up to 40% or more.

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Management strategy
In cold wet seasons rapid build-up of this disease occurs on both Polish and Argentine canola. Foliar fungicide for the control of sclerotinia will give moderate to good control of the black spot fungus. In dry years or in a succession of dry seasons this disease is virtually nonexistent on the canola crop. Disease build-up occurs in a succession of wet seasons.

Blackleg
Leptosphaeria maculans

What to look for?
Premature ripening of canola plants, lower stem lesions with pepper spot pycnidia and crop lodging.

Photo: Kharbanda	Picture description Pycnidia on seed; spore producing structures.	Photo: Petrie	Picture description Seedling infection; pepper spot infection of the cotyledonary leaf.
Photo: Petrie	Picture description Rosette infection causing death (girdling) of young plants.	Photo: Petrie	Picture description Leaf lesions showing typical of pepper spots.
Photo: Evans	Picture description Cankers on stems may girdle plant prior to maturity.	Photo: Evans	Picture description Major canker on stem.
Photo: Evans	Picture description Stem girdling canker causing stem breakage at flowering.	Photo: Petrie	Picture description Aerial infection on upper canola stems.
Photo: Evans	Picture description Overwintered canola stem producing ascospores and pycnidia spores.	Photo: Evans	Picture description Varietal resistance, Westar - foreground; Resistant cv. background.
Photo: Evans	Picture description Virulent strain - centre; other blackleg cultures avirulent.	Photo: Evans	Picture description Pinkish pycnidial ooze in vitro (petri dish).

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Management strategy
Resistance is rated at 1 through 5. One being highly resistant to the virulent strains of blackleg and five being very susceptible. Apparently a "new" virulent strain of blackleg is now present in Canada. Canola with rating of 1 or 2 may be quite susceptible to this new strain. Most if not all canolas are rated at 1, 2 or 3. For more information see Blackleg of Canola (FS149/632-3).

Foot and Root Rot
Fusarium sp. Rhizoctonia solani

What to look for?
An occasional sudden wilt disease of canola similar to Rhizoctonia or Pythium rot of bolted plants. A new Fusarium disease, F. avenaceum and F. oxysporum, is now showing up across the prairies. Affected plants are stunted sometimes followed by wilting and premature ripening. The development of symptoms on only one side of the stem is characteristic. Only a few canola cultivars seem to be affected at the present time.

Photo: Evans

Picture description
Fusarium root rot.

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Management strategy
Avoid planting known susceptible canola cultivars.

Fusarium Wilt of Canola - Frequently Asked Questions

Root Rot
Rhizoctonia solani

What to look for?
Severe lodging in a canola crop particularly on heavy waterlogged clay soils.

Photo: Evans

Picture description
Rhizoctonia foot rot of affected plants may break-off at soil level.

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Management strategy
Avoid planting canola in wet seasons on low lying heavy clay soils when possible. In seasons of good moisture canola is better suited to well drained soils.

Sclerotinia Stem Rot
Sclerotinia sclerotiorum

What to look for?
Premature ripening and moderate to severe lodging of the crop.

Photo: Evans	Picture description Sclerotia with seed; white interior when broken.	Photo: Evans	Picture description Apothecia germinates to form one or more 1 - 2 mm diameter apothecia (mushrooms) ascospore producing structures.
Photo: Evans	Picture description Volunteer canola in barley, note apothecia (mushrooms).	Photo: Evans	Picture description 10% bloom - 30% bloom in 3 - 6 days - i.e. full bloom when the most flowers are open.
Photo: Evans	Picture description 30% bloom equals full bloom when 20% of petals have dropped, 30% of flowers are open and 50% buds.	Photo: Evans	Picture description Axial infection - petals fall into axils and fungus grows from petals to infect the stem.
Photo: Evans	Picture description Stem infection leads to lodging.	Photo: Evans	Picture description Petal plating shows the abundance of ascospores on the petals.
Photo: Evans	Picture description Lodging - heavy losses up to 50% of the crop.	Photo: Evans	Picture description 50% infection - 25% yield loss on average.
Photo: Evans	Picture description Shredded stem - sclerotina infected.	Photo: Evans	Picture description Sclerotes in stem overwinter for next year's disease cycle.

Management strategy
Sclerotinia control in 35 bushel plus crops is achieved by foliar fungicides applied at full bloom (35% bloom when the maximum number of flowers are open). That means putting the maximum amount of fungicide on the most petals. Lighter seeding rates of the 1 1/2 to 2 lbs. an acre can produce fewer bigger plants less prone to lodging. For more information see Disease Forecasting for Sclerotina White Stem Rot in Canola (FS258/635-5)

Sclerotinia of Canola - Frequently Asked Questions

Birds Nest Fungus

What to look for?
This is a harmless saprophytic fungus that often colonizes old canola stems. The open fungus (mushroom) is about 3 times the size of the sclerotinia mushroom.

Photo: Evans

Picture description
Confused with Sclerotinia apothecia.

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Management strategy
None.

Seedling Blight
Rhizoctonia solani

What to look for?
Emergence failure, crop emerges and disappears especially in cold dry springs. Check also for flea beetles, cutworms and herbicide residues.

Seed treatment gives good control. Photo: Evans	Picture description Seed treatment gives good control.	Photo: Evans	Picture description Seedling blight (Pre-emergence).
Photo: Evans	Picture description Post emergent seedling blight.	Photo: Evans	Picture description Seedling blight injury is most severe on higher, dryer areas.
Photo: Evans	Picture description Continued injury from the Rhizoctonia fungus.	Photo: Evans	Picture description Rhizoctonia injury continues with plant maturity.
Photo: Evans	Picture description Top row: sterile soil; Mid row: canola - fallow - canola; Bottom row: canola continuous.

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Management strategy

White Leaf Spot / Gray Stem
Pseudocercosporella capsellae

What to look for?
A very gray appearance to the ripening crop.

Photo: Evans

Picture description
Grayish diseased stems.

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Management strategy
Despite appearances this disease does little damage to the canola crop.

White Rust / Staghead
Albugo candida

What to look for?
White rust on the seedling leaves and grossly distorted inflorescences.

Photo: Evans	Picture description White rust on underside of canola rosette leaves.	Photo: Evans	Picture description White rust on staghead flowering stem.
Photo: Evans	Picture description Mature dried staghead.

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Management strategy
This disease is strictly a problem in Polish (B. rapa) canola and B. jumcea mustard. Resistant varieties are available.

Sulphur Deficiency

What to look for?

Photo: Evans

Picture description
Cupped distorted leaves that occur in patches or over the whole field.

Photo: Evans

Picture description
Flowers are small, nonexistent deformed or pale yellow depending on degree of deficiency.

Management strategy
If herbicide residue injury is not the problem ammonium sulphate at 40 lbs. of S per acre may be applied up to the early bolt stage to immediately correct the problem. Ensure that the canola has adequate sulphur fertilizer levels. A comparable crop of canola has 3-4 times the sulphur requirements of barley or wheat.

Aster Yellows
Phytoplasma

What to look for?
Scattered individually damaged distorted plants that typically make up 1 to 2% of the crop. Occasional levels are more that 10% infection. Herbicide residue injury occurs in confluent patches or over the entire field.

Photo: Evans

Picture description
Distorted leaves, stems and flowers. Pods fail to fill out.

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Management strategy
None for this phytoplasma disease.

Bacterial Pod Spot
Pseudomonas syrigae

What to look for?
Water soaked pods.

Photo: Evans

Picture description
Water soaked lesions on the pods may also be caused by temperatures of -2^oC in late August. Check for dead seed later on in the season to confirm first injury.

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Management strategy
None at present.

Herbicide Damage
Many herbicides especially those in group 2 can cause canola injury.

What to look for?

Photo: Evans

Picture description
Glean damage.

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Management strategy
Be aware of your herbicide strategies and sensitive crop rotations. If in doubt have the soil bioassayed in late fall or very early spring.

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

For more information about the content of this document, contact Shelley Barkley.
This information published to the web on November 19, 2003.
Last Reviewed/Revised on November 6, 2017.