Blackleg appears as small grey lesions with black specks (fruiting bodies), found on the leaf surface of canola plants. In some cases the disease can produce cankers or lesions on the stem, weakening the plant and making it susceptible to lodging.
Prolonged wet weather may increase the spread and severity.
Blackleg is spread by rain splash of spores, by the wind or in some cases infected seed. Airborne sexual stage spores (ascospores) are produced on previous stubble residues and are released when conditions are optimal.
These spores are blown by the wind to infect developing canola plants, and the resulting lesions produce more spores which can be splashed on to nearby plants.
Prolonged wet weather may increase the spread and severity of the infection. Canola stem residues can be slow to break down in the soil due to their woody nature, and raking and burning may be necessary to provide acceptable stubble reduction.
A disease management plan of the following should be used:
- Treat seed with Quantum Pro to suppress the development of blackleg
- Do not grow successive canola crops in the same paddock
- Do not grow canola in paddocks adjacent to last season’s canola crop
- Grow varieties with a high blackleg resistance rating.