Phoma stem canker

Phoma stem canker, also known as blackleg, is a devastating disease caused by the fungal pathogen Phoma lingam (syn. Leptosphaeria maculans). It is classified within the Dothideomycetes class and represents a significant limiting factor for the production of brassicaceous crops globally.

The fungus affects a wide range of hosts, primarily oilseed rape (canola), cabbage, and broccoli. Symptoms typically begin as leaf spots containing pycnidia, which later progress into stem cankers near the soil line. Severe infections lead to lodging, premature ripening, and substantial yield loss due to systemic vascular disruption.

The life cycle involves two stages: the asexual pycnidial stage, which provides local spread, and the sexual ascomycete stage, which releases wind-borne ascospores. These spores can travel several kilometers, facilitating infection of healthy fields from infected crop debris left over from previous seasons.

Optimal development of the pathogen occurs under cool, wet conditions, particularly with frequent rainfall during the seedling and rosette stages. High humidity is essential for the germination of spores and penetration of the host tissue, often through natural openings or physical injuries caused by insects or machinery.

Integrated management is essential for effective control. Strategies include the selection of resistant cultivars, rigorous crop rotation to break the pathogen's life cycle, and the destruction of infected stubble through tillage. Fungicide applications during critical growth stages are recommended to suppress infection and protect the canopy from spore colonization.