Phomopsis stem canker of sunflower

Phomopsis stem canker (caused by the fungus Diaporthe helianthi) is a severe fungal disease affecting sunflower crops worldwide. It is characterized by the formation of necrotic lesions on leaves and stems, leading to weakened plant structure and substantial yield losses.

The disease primarily targets sunflower plants, though the pathogen can survive on various wild weeds, which serve as alternative hosts. The fungus colonizes all above-ground tissues, but the most devastating impact occurs when it invades the vascular system of the main stem, impeding the transport of water and nutrients.

Initial symptoms include dark, angular leaf spots that spread to the petioles. As the infection progresses, large gray-brown lesions appear on the stem, often centered at the point of leaf attachment. These cankers cause the tissue to soften and hollow out, leading to stem lodging and the premature death of the sunflower head before maturity.

The development of Phomopsis is highly dependent on environmental conditions, specifically warm temperatures (20–25°C) and high humidity or frequent rainfall. Ascospores produced by the fungus are dispersed by wind and splashing rain, allowing the disease to spread rapidly across fields. Overwintering occurs primarily in infected crop debris left on the soil surface.

The economic impact of Phomopsis includes both reduced seed weight and lower oil content. Effective disease management requires an integrated approach:

• Selection of resistant or tolerant sunflower hybrids.
• Crop rotation allowing a 6- to 8-year interval between sunflower plantings.
• Deep plowing to bury infested plant debris and accelerate decomposition.
• Prophylactic fungicide applications during the vegetative growth stages (V4 to V8).