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Canola
Diseases of the plant
By John David Converse
The Canola Plant
• Canola is a specific edible type of rapeseed, developed
in the 1970s, which contains about 40 percent oil.
• North Dakota leads the U. S. in canola production with
approximately 88 percent of domestic production.
The Canola Plant
• There are two types of canola varieties,
the Argentine type of the species Brassica
napus and the Polish type of the species
Brassica rapa. Argentine varieties have a
higher yield potential and are also taller
and have a higher oil content than Polish
varieties. Argentine varieties require about
95 days to reach maturity, while Polish
varieties need approximately 80 days to
reach maturity.
The Canola Plant
• Canola (Brassica napus L.) varieties have been
developed as both spring and winter annuals. The spring
type is best adapted to North Dakota conditions. The
winter types have not survived in trials in North Dakota,
northwestern Minnesota or in the prairie provinces of
Canada.
Rotation
• Canola best follows cereal grains or fallow
in rotation. A preferred crop rotation would
have canola planted at least two cropping
years between plantings.
• However, if planting canola after one
cropping year, it is strongly recommended
growing a variety that is moderately
resistant or resistant to blackleg.
Blackleg
• Blackleg is a common
disease that may cause
lodging.
• Blackleg produces black
lesions on the stem.
• The internal root tissues
of blackleg-infected
plants turn dark gray to
black or have dark gray
streaks in them.
• Blackleg infections near
the soil surface may
result in stem breakage at
or near the soil surface.
Blackleg
• The first symptoms
appear on the
cotyledons or leaves
as round-to-irregular
(1-2 cm) white-to-buff
lesions that contain
numerous small black
dots (pycnidia).
Blackleg
• As the season
progresses, the
fungus may spread to
the stem and crown of
the plant, producing a
canker that can girdle
the stem.
Blackleg
• Severely infected plants ripen prematurely
and have a black-to-grey discolouration at
the base of the stem or crown. In severe
cases, infected plants will lodge. Seeds of
severely infected plants are small and
shrivelled and may be infected with the
fungus.
Disease Cycle of Blackleg
• The blackleg fungus survives on canola
residues (refuse) and on infected plants
and seed. The fungus can be spread from
field to field on canola refuse or diseased
plants. The spores of the fungus are also
spread by rain, wind and infected seed.
Rotation
• Canola is susceptible to sclerotinia stem
rot. Infection risk increases if canola is
planted close in rotation with other highly
susceptible crops like sunflower, dry edible
beans, or crambe.
• At least two years should separate canola
and sugarbeet plantings. If planting canola
within three years of susceptible crops, a
fungicide application may be needed.
Rotation
• Less susceptible crops that could be planted
sucessfully in a close rotation with canola are
rowed soybeans, flax ,semi-leafless field pea or
lentil.
• In years when ideal environmental conditions
favor air-borne spore movement, all canola
plantings without fungicide applied, regardless of
rotation intervals, may have economic losses
due to sclerotinia.
Sclerotinia
• Sclerotinia stem rot
develops late in the
season, with the first
visual symptoms
appearing by the end
of flowering. Dead
and lodging plants
occur singly or in
patches in infected
fields.
Sclerotinia
• Infections of individual
plants usually develop
around cast petals. The
infections may produce a
target pattern of light
brown, mushy tissues.
Infections may spread
from infected leaf petioles
or branches to larger
stems. Infected areas
eventually become
bleached or white and the
tissues become
shredded.
Sclerotinia
• If the main stem is
infected, plants may
die early, reducing
seed production, and
plants may lodge.
Hard black bodies
which resemble rat
droppings may be
produced in infected
stems. These are
known as sclerotia
Sclerotinia
• Sclerotinia produces
shredded white stem
tissues with stem
bending or breakage
at a height of 6 to 18
inches above the soil
but no symptoms in
the roots
Disease Cycle of Sclerotinia
• The Sclerotinia fungus,
Sclerotinia sclerotiorum,
produces sclerotia in the
stems.
• If the soil is at or above
field capacity for 10 to 14
days, the sclerotia may
germinate to produce tiny
mushroom-like bodies
that resemble golf tees.
These fruiting bodies,
called apothecia,
produce millions of
airborne spores
Disease Cycle of Sclerotinia
• As canola petals die and
fall onto lower portions of
the plant, any spores on
the dead petals may
germinate and begin to
grow if the canopy stays
wet for long periods of
time. Once growth is
established on the cast
petals the fungus invades
the surrounding tissues.
Infections in canola may
continue to spread as
long as the canopy
remains wet.
Other Diseases
• Diseases of canola
less often reported
are white rust or
staghead, and downy
mildew.
Other Diseases
• Alternaria blackspot,
and aster yellows are
two other not as
common diseases in
Canola.
Final Thought
• Plant diseases can be a serious problem
in canola production. Rotations must be
planned carefully to keep disease
incidence and levels low.