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
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Lesions on pods and stems.

Photo: Evans
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Club-shaped Alternaria spores.

Photo: Evans
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Shattered pods caused by pod lesions - loss of yield can be up to 40% or more.

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
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Pycnidia on seed; spore producing structures.

Photo: Petrie
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Seedling infection; pepper spot infection of the cotyledonary leaf.

Photo: Petrie
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Rosette infection causing death (girdling) of young plants.

Photo: Petrie
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Leaf lesions showing typical of pepper spots.

Photo: Evans
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Cankers on stems may girdle plant prior to maturity.

Photo: Evans
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Major canker on stem.

Photo: Evans
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Stem girdling canker causing stem breakage at flowering.

Photo: Petrie
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Aerial infection on upper canola stems.

Photo: Evans
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Overwintered canola stem producing ascospores and pycnidia spores.

Photo: Evans
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Varietal resistance, Westar - foreground;
Resistant cv. background.

Photo: Evans
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Virulent strain - centre;
other blackleg cultures avirulent.

Photo: Evans
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Pinkish pycnidial ooze in vitro (petri dish).

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
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Fusarium root rot.

Management strategy
Avoid planting known susceptible canola cultivars.

Root Rot

Rhizoctonia solani

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


Photo: Evans
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Rhizoctonia foot rot of affected plants may break-off at soil level.

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
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Sclerotia with seed; white interior when broken.

Photo: Evans
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Apothecia germinates to form one or more 1 - 2 mm diameter apothecia (mushrooms) ascospore producing structures.

Photo: Evans
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Volunteer canola in barley, note
apothecia (mushrooms).

Photo: Evans
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10% bloom - 30% bloom in 3 - 6 days - i.e. full bloom when the most flowers are open.

Photo: Evans
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30% bloom equals full bloom when 20% of petals have dropped, 30% of flowers are open and 50% buds.

Photo: Evans
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Axial infection - petals fall into axils and fungus grows from petals to infect the stem.

Photo: Evans
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Stem infection leads to lodging.

Photo: Evans
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Petal plating shows the abundance of ascospores on the petals.

Photo: Evans
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Lodging - heavy losses up to 50% of the crop.

Photo: Evans
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50% infection - 25% yield loss on average.

Photo: Evans
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Shredded stem - sclerotina infected.

Photo: Evans
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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).

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
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Confused with Sclerotinia apothecia.

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.


Photo: Evans
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Seed treatment gives good control.

Photo: Evans
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Seedling blight (Pre-emergence).

Photo: Evans
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Post emergent seedling blight.

Photo: Evans
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Seedling blight injury is most severe on higher, dryer areas.

Photo: Evans
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Continued injury from the Rhizoctonia fungus.

Photo: Evans
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Rhizoctonia injury continues with plant maturity.

Photo: Evans
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Top row: sterile soil; Mid row: canola - fallow - canola; Bottom row: canola continuous.

White Leaf Spot / Gray Stem

Pseudocercosporella capsellae

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


Photo: Evans
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Grayish diseased stems.

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
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White rust on underside of canola rosette leaves.

Photo: Evans
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White rust on staghead flowering stem.

Photo: Evans
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Mature dried staghead.

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

Sulphur Deficiency


Photo: Evans
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Cupped distorted leaves that occur in patches or over the whole field.

Photo: Evans
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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
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Distorted leaves, stems and flowers. Pods fail to fill out.

Management strategy
None for this phytoplasma disease.

Bacterial Pod Spot

Pseudomonas syrigae

What to look for?
Water soaked pods.


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


Management strategy
None at present.

Herbicide Damage

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


Photo: Evans
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Glean damage.

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.