A fungus called Sclerotinia sclerotiorum causes this disease.
Why Does it Matter?
- Sclerotinia occurs on all canola growing regions and is the most economically significant disease of canola in Western Canada.
- Yield loss. Depending on weather conditions, yield losses can be extremely high.
A rule of thumb is that yield loss is about half of the percentage of infected plants in the field. A field with 20% infected plants, therefore, will result in a 10% yield loss. - Grade loss. Tolerances for sclerotinia are very low. Table 7 of the Canada Seed Act, which applies to mustard and canola, has a separate standard for sclerotia. When performing a purity analysis on the crop, sclerotial bodies are reported per 50 grams. The standards are as follows:
Grade — Maximum number of sclerotial bodies per 50g
Canada Foundation No. 1 — 1
Canada Foundation No. 2 — 2
Canada Registered No. 1 — 1
Canada Registered No. 2 — 2
Canada Certified No. 1 — 1
Canada Certified No. 2 — 2
Common grade — 2
What are the Symptoms?
- Onset of infection begins as water rot on stems and/or leaves.
- On standing crops, look for light brown lesions on stems, branches and pods.
- These lesions expand and become bleached-looking and may have concentric rings.
- When lesions expand enough to girdle the stem, plants will wilt.
- The bleached stems tend to shred and break at the base.
- Hard, black overwintering bodies (sclerotia) form inside the infected stems and pods.
What is the Disease Cycle?
- The black sclerotia produced inside infected plants can live in the soil for at least 4 to 5 years.
- Under suitable conditions the sclerotia germinate and produce tiny cup-shaped mushrooms (apothecia).
- The apothecia produce thousands of air-borne spores that can be blown several kilometers into adjacent fields.
- Sclerotia that form in infected seedpods closely resemble canola seed in size and shape and may be harvested with, and then planted with, the seed the following season.
- The fungus may also be seed-borne.
How is it Controlled?
- Use good quality, clean seed that is free of sclerotia.
- Observe crop rotations of at least 4 years and, if possible, do not include other susceptible crops such as pea, sunflower, mustard, lentil, bean chickpea, alfalfa, clover, carrot or potato.
- Select varieties that have fewer flower petals and good lodging ratings.
- Control volunteer canola and broadleaf weeds during rotations.
- Remove sclerotia using a spiral spinner.
- Deep burial of infected stubble (at least 8 cm).
- Apply registered foliar fungicides at 10% to 50% bloom if a disease forecast warrants this procedure.
How Does 20/20 Seed Labs Inc. Test for Sclerotinia in Canola?
Purity test
- 20/20 Seed Labs Inc. routinely checks for and reports the presence of sclerotia during a seed purity test
Culture test
- 200 seeds are surface sterilized to remove surface contaminants from the seed coat then placed on culture agar plates and incubated for 7 days.
- A qualified staff member examines the plates for the presence of the Sclerotinia sclerotiorum. The type of mycelium produced and the presence of sclerotia forming on the plate identify this fungus.
- This test gives the percentage of infected seeds to 0.5%.
- This test takes 7 days to complete.
Please contact us for more information.
