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Sclerotinia – what to watch
for, how to manage
Faye Dokken-Bouchard
Provincial Specialist, Plant Disease
Saskatchewan Ministry of Agriculture
1
What is disease?
• Plant diseases are
caused by:
– Pathogens
•
•
•
•
Fungi
Bacteria
Viruses
Phytoplasmas
– Nematodes
– Environmental stress
• Leads to signs and
symptoms of disease
2
What impacts do diseases have?
• Ultimately affect crop
quality & yield
– Reduce photosynthesis
– Result in flower and
head infections
R. Kutcher
3
What impacts do diseases have?
• Ultimately affect crop
quality & yield
– Reduce root
growth/uptake
– Restrict stem flow
4
What is Sclerotinia?
• Pathogen = Sclerotinia
sclerotiorum
• Found in most parts of
the world with a large
host range that includes
over 400 plant species in
75 broad-leaf families.
• Diseases = sclerotinia
rot, white mould, stem
rot, watery soft rot,
drop, or blossom blight.
• Host field crops include
canola, mustard, flax,
sunflower, pea, bean,
lentil, chickpea, forage
legumes, vegetables, and
related broadleaf weeds.
What to watch for?
• Sclerotia produce apothecia that
release spores infecting petals or
aboveground plant tissues, leading
to a soft watery rot.
• As lesions advance they may
resemble a "bull's eye" pattern of
concentric rings of rotting tissue.
• Infected stems often become
bleached and will easily shred.
• Sclerotia can also germinate to
produce fungal strands that infect
the root system directly, resulting in
damping off or root rot.
What to watch for?
• Under wet conditions, white fungal
growth or mould can be found on
leaves, stems pods and fruits.
• Mould can spread from plant to
plant via direct contact, thus lush,
dense crop canopies favour disease.
• As the disease advances and host
tissues are destroyed, sclerotinia
produces the hard, black sclerotia on
the surface of plant tissues and
within stems and roots.
• Rotting of stored crops, such as
carrots, can continue under damp,
confined conditions.
Sclerotinia in Sunflower
• Sclerotinia can be
devastating when
sunflower crops are
produced in regions
where other broad-leafs
are common.
• Sunflowers may develop
root infections, which
lead to stem breakage,
or head infections, which
affect seed yield and
quality.
Sclerotinia in Pulses
• Plant tissue such as older flowers or
possibly lower leaves that have died
from other causes are likely to
become infected first and spread to
healthy pods, stems and leaves
through direct contact.
• Sclerotinia infection in pulses leads
to stem and pod rot, crop lodging
and reduced seed fill, seed-borne
disease and quality issues.
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R. Morrall
Sclerotinia in Forages
• Forage legumes such as
alfalfa grown for seed may
also be affected by
sclerotinia.
• Blossom blight is a disease
of the flowers that is caused
by a combination of
Sclerotinia sclerotiorum and
Botrytis cinerea, leading to
blossom abortion and seed
yield loss.
B. Gossen
Sclerotinia in Other Plants
• Sclerotinia has also been
observed on specialty crops in
Saskatchewan including hemp,
echinacea, biennial caraway.
• A number of broad-leaf weeds
are also hosts and may
maintain the fungus in the soil
Source unknown
even when non-host crops are
grown (e.g. stinkweed, sowthistles, • Vegetables affected include
beans, cole crops, curcurbits,
Canada thistle, wild mustard, redroot
carrots, celery, lettuce, peas,
pigweed, knapweeds, dandelions,
radish, rutabaga, turnips,
lambsquarters, etc…).
rhubarb, potatoes and tomatoes.
Sclerotinia in Canola
81 % of crops surveyed in SK in 2011 had at least a trace of
sclerotinia (91% in 2010), with an overall incidence (percentage
of plants with disease) of 9% (20% in 2010) or 12% in infected.
12
K. Turkington
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REGION
(NO. OF FIELDS)
North-west
(21)
CANOLA Sclerotinia
Incidence
6 {20}
Severity
2.4 {3.0}
North-east
(66)
11 {20}
3.2 {2.5}
West-central
(58)
10 {22}
2.2 {2.4}
East-central
(65)
10 {22}
2.2 {2.4}
South-west
(15)
11 {15}
1.6 {2.0}
South-east
(16)
2 {12}
Overall mean (241)
9% in
2011
2.4 in
2011
{20% in
2010}
{2.5 in
2010}
Lesion
Location
CANOLA Symptoms
0
None
No symptoms
1
Pod
Infection of pods only
Disease
Rating
2
Lesion situated on main
stem or branch(es) with
potential to affect up to ¼ of
seed formation and filling on
plant
3
Lesion situated on main
stem or on a number of
branches with potential to
affect up to ½ of seed
formation and filling on plant
Upper
4
Lesion situated on main
stem or on a number of
branches with potential to
affect up to ¾ of seed
formation and filling on plant
5
Main stem lesion with
potential effects on seed
Lower
formation and filling of entire
Sclerotinia
rating scale (Kutcher and Wolf 2005).
plant
0.9 {2.0}
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Values represent average across all crops
15
16
Trending Sclerotinia Incidence in
Saskatchewan (1999-2011)
35
30
25
20
15
North-east
North-west
East-central
West-central
South
Province
10
5
0
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Fungal Facts: why do we see more
disease in wet years?
• Most plant diseases occurring in
western Canada are caused by
Primary
Overwinter
fungal organisms.
Inoculum
Stage
• Fungi may live as saprophytes
(break down dead material) or
pathogens (infect/feed on living
hosts) or both (opportunistic).
Secondary
• In general, most fungi like warm,
Inoculum
moist conditions and rich
Symptoms
Infection
nutrient sources.
• Excess moisture can also affect
plant susceptibility to disease
Growth &
(through stress or length of
Reproduction
susceptible growth stages).
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Will Flooding Reduce Sclerotinia?
• Sclerotia are made to resist adverse conditions… but they
will lose viability and/or rot eventually!
– Under dry moderate temperature conditions, 65% of the
normal sclerotia produced will remain viable after 5 years
(Huang et al)
– After two years, 65% of sclerotia rotted at high soil moisture,
compared to 45% of sclerotia at low soil moisture (Teo et al)
• But remember… for the surviving sclerotia, wet
conditions will be conducive for disease.
22
How to manage?
•
•
•
•
•
Crop rotation & disease tolerant cultivars
Prevention & sanitation measures
Seedling health & seed treatments
Crop scouting & foliar fungicides
Good record keeping & planning
• Which tools are most appropriate
for sclerotinia management?
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How to manage?
• Good record keeping
– Past experience helps determine future risk.
• Manage disease inoculum
– Lengthen rotations in affected fields.
– Contans
• Sclerotinia tolerant varieties
• Watch for rain showers when you start to see
canola flowers (rain in last 2 weeks and in
forecast increases risk)
• Crop Scouting - look for apothecia  
• Consider spraying fungicide around 20 to 50%
flowering for canola
– Too early – flowers will not be open (sclerotinia
can only initiate disease in canola through petals)
– Too late – less chance of yield benefit (although
late infections may result in symptoms)
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Sclerotinia Risk Maps – weatherbug.com
This risk applies ONLY to canola in flower. The model is based on the
development of sclerotia bodies (apothecia mushrooms) under the canola
canopy. The risk map is of regional nature and further inspection of the canola
crop should occur with regard to growth stage and canopy coverage.
Petal Testing
• The petal test kit was developed by
the University of Saskatchewan to
serve as a risk assessment tool for
estimating disease severity based on
the percentage of canola petals
infected by sclerotinia ascospores.
• If more than 45 per cent of canola
petals are infected with the fungus,
the crop density is high, canola price
is moderate to high, and moist
conditions are expected, then yield
loss would likely warrant a fungicide.
• The kit is only effective if used at the
early bloom stage to allow time to
make a management decision
regarding fungicides.
Sclerotinia Check List
• A checklist developed in Sweden and adapted by
the Canola Council of Canada can help assess
disease risk. Growers should fill out the checklist
for each field shortly after first flower (when 75%
of the canola plants have at least 3 open flowers).
See CCC website.
• The greater the risk score for a field the higher
the probability of a positive economic return.
Fields scoring 40 or higher will likely benefit from
a fungicide, but this may vary a bit depending on
fungicide cost and commodity price.
Spraying for Sclerotinia Canola
Possible Answers Risk Points
Number of years
since last host
crop
> 6 yrs
0
3 – 6 yrs
5
1 – 2 yrs
10
Disease
incidence in last
host crop
None
0
Low (1-10%)
5
Moderate (1130%)
10
High (31-100%)
15
Low
0
Normal
5
High
10
Crop Density
Example
10
10
5
Total = 25
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Spraying for Sclerotinia Canola
Possible Answers Risk Points
Rain in last 2
weeks
<10mm (0.4”)
0
10-30 mm (0.41.2”)
5
>30mm (1.2”)
10
Weather forecast High pressure
Apothecial
Development
Example
5
0
Variable
10
Low pressure
15
None found
0
Low numbers
10
High numbers
15
10
10
Total = 25+25=50
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Spraying for Sclerotinia Canola
Possible Answers Risk Points
Number of years
since last host
crop
> 6 yrs
0
3 – 6 yrs
5
1 – 2 yrs
10
Disease
incidence in last
host crop
None
0
Low (1-10%)
5
Moderate (1130%)
10
High (31-100%)
15
Low
0
Normal
5
High
10
Crop Density
Example
5
5
5
Total = 15
30
Spraying for Sclerotinia Canola
Possible Answers Risk Points
Rain in last 2
weeks
<10mm (0.4”)
0
10-30 mm (0.41.2”)
5
>30mm (1.2”)
10
Weather forecast High pressure
Apothecial
Development
Example
5
0
Variable
10
Low pressure
15
None found
0
Low numbers
10
High numbers
15
10
0
Total = 15+15=30
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When to Stop Spraying – Crop
Considerations
• Variety: sclerotinia resistant/tolerant canola (no
resistance in pulses)
• Staging for canola: Spray at 20 to 50 per cent bloom,
as the fungicide needs to cover the petals in order to
protect against sclerotinia.
– By the time you see symptoms of sclerotinia, it is too late
to spray. The earlier the infection takes place the more
potential damage; therefore spray to protect the most
blossoms at the earliest stage. Petals infected after 50 per
cent bloom may still lead to disease but the impact will be
less intense as the petals are likely to drop into the upper
canopy and have less time for the disease to progress.
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When to Stop Spraying –
Disease Severity
• Is disease present? Fungicides cannot cure disease. If
effective control has not been achieved during the
season and symptoms are already widespread, it is
usually too late to apply a fungicide.
• Has the crop been damaged by other factors? Are
there other reasons it may not be worth saving? Do
you expect the crop to recover?
• Crops often recover from early damage such as hail;
BUT if significant injury occurs during podding/seed
development, it may not be worth saving.
33
When to Stop Spraying –
Weather Conditions
• Warm dry weather will naturally control
diseases as well as help progress the crops to
maturity.
• Cool wet weather will often favour disease
and potentially delay maturity.
34
When to Stop Spraying –
Estimated Yield / Value
• What disease impact are you expecting and to
what degree do you anticipate that a fungicide
will improve the crop yield/quality?
• Will you make enough money after harvest to
pay for the application(s)?
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When to Stop Spraying – Other
Considerations
• Have you used a proper fungicide rotation to prevent
fungicide resistance?
• Are you too close to harvest? Follow the recommended preharvest interval of the fungicide (check the Guide to Crop
Protection or product label). Some examples:
Allegro (fluazinam): beans 30 days
Astound (cyprodinil + fludioxonil): canola 35 days
Lance (boscalid): pulses and canola 21 days
Proline (prothioconazole): canola 36 days, chickpea and lentil 7 days
Quadris (azoxystrobin): canola 30 days, coriander 21 days, pulses 15
days
– Rovral Flo/RX (iprodione): canola 38 days
– Serenade (biofungicide): can be applied up to harvest
–
–
–
–
–
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Spraying for Sclerotinia
Product
Allegro
Astound
Lance
Proline
Quadris
Rovral Flo
Senator
Serenade
Contans
Canola


Other
Beans only
Pulses & seed
alfalfa
Pulses


Seed alfalfa

Beans only
Pulses & potatoes

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Soil application to sclerotia (3 months prior)
Disease ID Resources
• Diseases of Field Crops in
Canada
– Information on all crop
diseases and photos
• Ministry of Agriculture
– Fact sheets (various
crops/diseases/photos online)
– Crop Production News during
the field season
• Canola Council of Canada
– Fact sheets, Grower’s Manual,
Canola Watch
– Guidelines on all aspects of
canola agronomy including
disease scouting and photos
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Thank you!
Faye Dokken-Bouchard
306-787-4671
[email protected]
Acknowledgements:
Ministry of Agriculture – Regional & Crops Branch Specialists
Saskatchewan Canola Disease Surveyors
Canola Council of Canada
Council ofof
Canada
All photos by F. Dokken-Bouchard,Canola
Ministry
Agriculture, unless otherwise noted.
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Sclerotinia Webinar 2011