Angular leaf spot of bean

Angular leaf spot is a destructive disease of beans caused by the fungus Pseudocercospora griseola. This pathogen is globally distributed and is particularly problematic in tropical and subtropical bean-producing regions, where it significantly impacts crop productivity.

The disease affects common beans and other legume species. It attacks all aerial parts of the plant, including leaves, stems, petioles, and pods. In severe cases, the entire plant architecture can be compromised, leading to massive defoliation and severe yield reductions in both biomass and seed quality.

Symptoms initially appear as small, gray-to-brown spots on the leaves, which become angular as they are restricted by the leaf veins. In humid conditions, dark-colored fungal growth (conidiophores and conidia) can be observed on the underside of these spots. Similar lesions occur on stems and pods, often leading to reduced pod filling and discolored seeds.

Environmental conditions are crucial for the development and spread of Pseudocercospora griseola. High relative humidity and temperatures ranging from 20°C to 28°C create the perfect environment for sporulation and infection. The fungus survives as mycelium or spores in infected crop residues in the soil and is frequently disseminated through infested seeds, which are the primary source of initial infection.

• Implement a strict crop rotation of 3 years or more to break the disease cycle.
• Utilize high-quality, pathogen-free, or fungicide-treated seeds for planting.
• Incorporate crop residues into the soil to accelerate decomposition and reduce inoculum.
• Apply protective or systemic fungicides when environmental conditions favor disease onset.
• Plant resistant or tolerant bean varieties to minimize the risk of yield loss.