Phoma stem canker

Phoma stem canker, caused by the fungus Plenodomus hendersoniae (commonly associated with the complex of Leptosphaeria maculans), is a devastating disease affecting oilseed rape and other brassica species worldwide. The fungus is a necrotrophic pathogen that can lead to total crop failure if left unmanaged in conducive environmental conditions.

The host range includes various brassica crops, with winter oilseed rape being the most economically significant. The fungus attacks all stages of development, from seedling emergence to maturity. By infecting the stem base, the pathogen restricts water and nutrient transport, leading to severe yield losses through lodging and plant death.

Symptoms typically begin on leaves as pale-grey circular spots speckled with black pycnidia, which serve as inoculum sources for further infection. As the fungus progresses, it moves from the leaves down to the petiole and enters the stem. The resulting phoma lesions at the base of the plant can girdle the stem, causing internal decay and structural weakness.

The disease thrives in environments characterized by mild temperatures and frequent rainfall. Rain-splash is the primary mechanism for the dispersal of conidia from infected stubble to new foliage. Warm, wet autumns are particularly favorable for early infection, allowing the fungus to establish itself in the crown of the plants before winter dormancy.

• Implementation of a wide crop rotation to reduce inoculum in the soil.
• Growing resistant or tolerant cultivars with high levels of genetic resistance.
• Deep burial of crop residues to accelerate decomposition of infected material.
• Timely fungicide applications based on local disease thresholds and scouting.
• Monitoring fields for leaf spot development during early growth stages.