Phoma black stem of sunflower

The causal agent of Phoma black stem of sunflower is the fungus Vacuiphoma bulgarica. This pathogen is a significant threat to sunflower production worldwide, capable of infecting the crop at various stages of growth and causing severe damage to stem integrity.

The primary host for this fungus is the sunflower plant. The pathogen survives primarily in soil and crop debris from previous seasons, which serves as the main source of inoculum for new infections when environmental conditions become favorable.

Symptoms typically manifest as dark brown or black lesions on the leaves, which eventually migrate to the leaf petioles. As the disease progresses, large black spots appear on the stem, often at the base or at the nodes. These lesions can girdle the stem, leading to vascular disruption and premature wilting of the plant.

Disease development is heavily influenced by high humidity and moderate temperatures, typically between 20°C and 25°C. Rainfall events facilitate the splash dispersal of pycnidiospores from infected lower leaves to the upper parts of the plant, accelerating the epidemic across the field.

The economic impact of Phoma black stem is substantial, as it significantly reduces photosynthetic capacity and nutrient uptake. This leads to poor seed filling, lower overall yield, reduced oil content, and weakened stems that are prone to lodging, complicating the harvesting process.

• Strict adherence to crop rotation cycles of at least 4–7 years.
• Planting of resistant or tolerant sunflower hybrids.
• Effective management of crop residues through deep tillage.
• Application of foliar fungicides during early vegetative growth stages.
• Control of volunteer sunflowers and weeds that may harbor the pathogen.