Spring and Winter Canola: Blackleg

Excerpt from Agronomy Guide for Field Crops (Chapter 8)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Incidence
2. Appearance
3. Disease Cycle
4. Management Strategies
5. Updates on Spring and Winter Canola: Blackleg

Incidence

Blackleg is a fungal disease that occurs in all canola-growing regions of Canada. In Western Canada, two strains (mild and virulent (severe)) of the fungus are found. As a result, substantial losses occur in Western Canada from the disease. In recent years, blackleg has been increasing in Ontario, especially in winter canola fields. Fortunately, the severe or virulent strain responsible for losses in the West has not been identified, to date, in Ontario.

| Top of Page |

Appearance

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).

Plate 142. Blackleg causes round-to-irregular, white-to-buff lesions containing many black dots (pycnidia).

As the season progresses, the fungus may spread to the stem and crown of the plant, producing a canker that can girdle the stem.

Plate 143. Blackleg spreads to the stem, producing a canker that girdles the lower stem.

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.

| Top of Page |

Disease Cycle

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.

Management Strategies

Use less susceptible varieties. Most varieties are rated on a 1 (resistant) to 5 (highly susceptible) scale. Maintain a good crop rotation that has at least 3 years between canola crops. Fungicide seed treatments will reduce seed-borne infection and minimize the risk of introducing blackleg into new fields. However, the disease can still be spread from field to field on infected plants and refuse.
Refer to the OMAFRA Publication 812, Field Crop Protection Guide, for recommended seed treatment options. (Order OMAFRA Publication 812)

| Top of Page |

Updates on Spring and Winter Canola: Blackleg

• Field Crop Protection Guide - Publication 812
  • Canola and Mustard: Blackleg

Related Links

• Canola
• Diseases

| Top of Page |