Pleospora bjoerlingii

Pleospora bjoerlingii (anamorph: Phoma betae) is a destructive fungal plant pathogen belonging to the Dothideomycetes class. It is the primary cause of Phoma leaf spot and root rot, significantly impacting sugar beet, fodder beet, and chard production worldwide.

The pathogen causes a range of symptoms, including circular necrotic lesions on foliage and dry rot on the crown and roots of mature plants. In seedlings, it manifests as damping-off or «black leg,» which frequently results in poor crop establishment and necessitates costly reseeding operations.

The biology of this fungus is complex, involving both sexual and asexual stages. Pycnidia, which produce conidia, are the primary inoculum for spreading the disease during the growing season, while pseudothecia allow the fungus to survive adverse conditions on crop debris and in the soil.

Favorable conditions for the development and spread of Pleospora bjoerlingii include high humidity, prolonged wet weather, and moderate temperatures. The fungus readily infects plants that are stressed by nutrient deficiencies, pest pressure, or unfavorable soil conditions, leading to rapid disease progression.

Control strategies should focus on integrated pest management (IPM) practices. Key measures include the use of high-quality, fungicide-treated seeds, implementing a long-term crop rotation that avoids beet-to-beet cycles, ensuring balanced soil fertilization (especially boron), and meticulous sanitation to reduce the primary inoculum in the field.