Cercospora leaf spot of faba bean

The disease is caused by the fungal pathogen Cercospora zonata, which belongs to the class of mitosporic fungi. It is a widespread pathogen known for attacking the aerial parts of plants, primarily leaves and stems. The fungus overwinters as mycelium and conidia in infected crop residues and can remain viable in the soil for several growing seasons.

The primary host for this fungus is the faba bean (Vicia faba). While it may occasionally be identified on related leguminous plants, its economic significance is highest in faba bean cultivation. Severe infections can lead to significant biomass loss, which directly impacts the overall health and yield potential of the crop.

Symptoms initially appear as small, circular or irregular spots on leaves. These spots typically exhibit a distinctive zonate pattern with alternating dark and light brown rings, surrounded by a yellowish halo. As the disease progresses, these lesions enlarge and coalesce, eventually causing leaves to wither and detach from the plant prematurely.

The development of Cercospora zonata is strongly favored by high relative humidity (above 80%) and moderate temperatures ranging from 20 °C to 25 °C. Leaf wetness duration from dew or frequent rainfall is critical for conidial germination and penetration. Field conditions such as dense plant spacing and poor aeration significantly increase the risk of an outbreak.

The economic impact of the disease is linked to reduced photosynthetic efficiency, leading to stunted plants and shriveled seeds. Effective management requires an integrated approach: using disease-free seeds, ensuring proper crop rotation, and removing infected debris. Foliar fungicides are essential during periods of high disease pressure to maintain crop productivity.

• Implement a 3–4 year crop rotation cycle.
• Ploughing down crop residues to limit inoculum sources.
• Monitoring field plots for early necrotic leaf spot symptoms.
• Application of approved chemical fungicides during high-risk weather.