Rice narrow brown leaf spot

Narrow brown leaf spot is a significant fungal disease of rice caused by the pathogen Cercospora janseana (formerly known as Cercospora oryzae). It belongs to the group of foliar diseases that can cause substantial yield losses in rice-growing regions globally by reducing the plant's photosynthetic capacity.

The primary host for Cercospora janseana is rice (Oryza sativa). The fungus survives between seasons as mycelium in infested crop residues and on infected seeds. The pathogen is widespread in both temperate and tropical rice-producing areas where environmental conditions favor the development of fungal spores.

The symptoms appear as narrow, linear, brown to reddish-brown lesions on the leaf blades. These lesions are typically restricted by leaf veins, giving them a distinct shape. As the infection progresses, the lesions may coalesce, leading to severe chlorosis or necrosis of the leaf, which eventually results in the leaves dying prematurely and negatively impacting grain filling.

Disease development is highly dependent on environmental factors, particularly humidity and temperature. Warm temperatures between 25°C and 30°C and periods of high humidity are ideal for the production and dispersal of conidia. Rain splash and wind act as primary vectors for spreading the spores throughout the field during the growing season.

Effective management and prevention of the disease rely on a combination of cultural and chemical strategies:

• Planting resistant or tolerant rice varieties suitable for the region.
• Implementing field sanitation by destroying or incorporating infected crop stubble.
• Maintaining healthy crop growth through balanced fertilization and proper water management.
• Using certified, disease-free seeds to prevent primary inoculum introduction.
• Applying recommended fungicides when environmental conditions pose a high risk of infection.