Phoma stem canker

Phoma stem canker, often referred to as black leg, is a devastating fungal disease caused by the pathogen Leptosphaeria maculans. This disease primarily affects oilseed rape and radish, causing significant yield losses in many agricultural regions worldwide. The fungus persists in the soil on infected crop residues, serving as a primary reservoir for new infections every season.

The symptoms of the disease are diverse and evolve throughout the growing season. Early signs include pale leaf spots containing small, dark pycnidia. As the infection progresses, it colonizes the stem base, creating necrotic lesions or cankers. These lesions restrict nutrient and water transport, leading to wilting, plant lodging, and in severe cases, plant death before harvest.

Environmental conditions play a critical role in the development and spread of the pathogen. Warm, humid weather combined with frequent rainfall facilitates the release and dispersal of spores, which are transmitted by wind and rain splashes. The initial infection often starts on lower leaves during the autumn, followed by systemic migration toward the plant stem.

The economic impact of Phoma stem canker is substantial. Severe outbreaks can lead to premature senescence and significant reductions in seed weight and oil content. The inability of the root system to support the plant due to stem girdling often causes crop failure in localized areas, reducing overall profitability for the producer.

Effective management requires an integrated approach. Farmers should prioritize the use of resistant crop varieties and strict crop rotation cycles to break the life cycle of the fungus. Chemical control using fungicides, particularly when applied at the critical seedling stage (typically 4-6 leaves), is essential for maintaining plant health and preventing the upward movement of the pathogen.

• Choosing resistant germplasm
• Managing crop stubble to reduce inoculum
• Timely fungicide applications
• Monitoring weather patterns for disease risk