Narrow brown leaf spot

Causative agent

Fungus, Sphaerulina oryzina, (Cercospora janseana)

Plant parts and life stages affected

Leaf blades,  leaf sheaths, pedicels and glumes

Severity of the disease varies in from year to year and is more severe as rice plants approach maturity.

Severity might also vary based on level of varietal susceptibility. This disease may and cause severe leaf necrosis, some premature ripening, yield reduction and lodging.

Symptoms

Typical lesions on leaves and upper leaf sheath are light to dark brown, linear, and progress parallel to the vein. They are usually 2−10 mm long and 1−1.5 mm wide.

Lesions on the leaves of highly susceptible varieties may enlarge and connect together, forming brown linear necrotic regions.

On glumes, lesions are usually shorter but can be wider than those on the leaves. Brown lesions are also found on pedicels.

The disease also causes discoloration on the leaf sheath, referred to as “net blotch” because of the netlike pattern of brown and light brown to yellow areas.