Phoma leaf and stem spot of sunflower

Subplenodomus drobnjacensis is the causal agent of Phoma leaf and stem spot of sunflower. This fungal pathogen is one of the most economically significant threats to sunflower production globally, capable of affecting all growth stages and causing yield losses of up to 50% under favorable conditions.

The fungus is host-specific, primarily targeting species within the Helianthus genus. While it is most commonly associated with commercial sunflower crops, it can survive on alternative hosts and crop debris, making it a persistent challenge for agricultural systems where proper crop rotation is not strictly followed.

Symptoms typically begin on lower leaves, manifesting as dark, necrotic lesions. As the pathogen progresses, these lesions spread to the stem, specifically around the leaf axils. The characteristic dark, coal-like patches on the stems weaken the plant structure, leading to premature senescence and mechanical breakage.

Environmental factors play a crucial role in disease epidemiology. High humidity, frequent rainfall, and moderate temperatures ranging between 20°C and 25°C trigger the production of pycnidia. These structures release spores that are disseminated via rain splash and wind, facilitating rapid disease spread across the field.

Integrated disease management is essential for minimizing impact. This includes the deployment of resistant sunflower hybrids and the strict management of crop residues. Fungicide applications during the vegetative stages are often necessary in high-pressure areas. Furthermore, seed treatments can help prevent the introduction of the pathogen into new areas through infected seeds.