Canola Watch quiz – Pre-harvest disease scouting

The best time to survey canola fields for disease incidence and severity is just before swath timing – which is 50-60% seed colour change on the main stem. If not swathing, you can still use this crop-stage timing to check for disease. Some fields across the Prairies are at this stage. The rest will follow over the coming weeks.

At the swath-timing stage, any diseases present will be near peak intensity and fairly easy to identify. This will provide an accurate assessment of disease, which can be used to enhance long-term management decisions (such as disease-resistant seed choices, crop rotations and fungicide use). It could also be used to make harvest timing decisions for this year.

The following quiz questions (and detailed answers) will help you identify the disease symptoms you’re seeing.

1. Fill in the blank. ____________ goes through petals to leaves to stems, annihilating tissue with acid as it goes, drinking in the death of plant cells.

Sclerotinia sclerotiorum (Sclerotinia stem rot pathogen)

Leptosphaeria maculans (Blackleg pathogen)

Plasmodiophora brassicae (Clubroot pathogen)

Verticillium longisporum (Verticillium pathogen)

2. Fill in the blank. _________ goes through leaves and stems via the xylem without causing much damage, until it hits the crown. Then it leaves the xylem and destroys all host tissue there.

S. sclerotiorum (Sclerotinia stem rot pathogen)

L. maculans (Blackleg pathogen)

P. brassicae (Clubroot pathogen)

V. longisporum (Verticillium pathogen)

3. Fill in the blank. __________ infects roots, traveling up the xylem feeding on xylem sap as it goes, multiplying until it chokes the plant mid-stem. Once plant begins to die it fills the xylem with microsclerotia which eventually busts out of the epidermis.

S. sclerotiorum (Sclerotinia stem rot pathogen)

L. maculans (Blackleg pathogen)

P. brassicae (Clubroot pathogen)

V. longisporum (Verticillium pathogen)

4. When scouting for blackleg severity, you want to clip through the canola crown to see what percentage is blackened. What is the ‘crown’?

The top part of the stem, where the pods are

The area of the stem immediately below the bottom-most branch

Where the root and stem meet

Immediately above the first root

5. While doing the pre-harvest scout for disease incidence and severity, take a look for anything else unusual. In moist conditions, you might see symptoms like those shown in the photo below. What caused these symptoms?

 

Aphid frass

Calcium deficiency

Frost

Powdery mildew

6. If a patch of canola is drying down prematurely but shows no other above ground symptoms, it could be:

Clubroot

Excess moisture

Lack of moisture

Nitrogen deficiency

Any of the above

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