Phoma leaf spot and stem rot of sunflower

Nothophoma infossa is the causal agent of Phoma leaf spot and stem rot, a significant fungal disease affecting sunflower crops globally. Formerly categorized as Phoma macdonaldii, this pathogen belongs to the Phomataceae family and is responsible for substantial yield losses in agricultural production.

The primary host for this fungus is the cultivated sunflower (Helianthus annuus). The disease attacks various parts of the plant, including leaves, stems, and petioles. It can infect plants at different growth stages, making it a persistent challenge throughout the vegetative cycle of the crop.

Initial symptoms include dark brown or black lesions on the lower leaves. As the infection progresses, large necrotic spots appear on the stem, often starting at the base. These lesions weaken the structural integrity of the plant, frequently resulting in stem breakage and lodging, especially under windy conditions.

Favorable conditions for the development of Nothophoma infossa are characterized by warm temperatures and high humidity or frequent rainfall. The fungus overwinters on crop residues and in the soil, allowing spores to be disseminated by splashing rain, wind, and insects when environmental conditions improve.

The economic impact of the disease is profound, causing significant reductions in seed yield and oil content. Infected plants wither prematurely, and the disruption of vascular tissues prevents the proper filling of the sunflower head, leading to light, empty, or shriveled achenes.

Effective management strategies rely on integrated pest management practices. Key recommendations include rotating crops with non-host species, deep plowing to bury infested residue, using certified seeds, and applying fungicides preventively. Selecting resistant hybrids remains the most sustainable method for long-term disease mitigation.