Rice sheath rot

The fungus is currently known taxonomically as Sarocladium oryzae. It is a filamentous fungus that produces slender, hyaline conidiophores, often arranged in bundles, which generate large quantities of conidia under humid conditions.

The pathogen specifically infects rice plants (Oryza sativa). It primarily targets the leaf sheaths that enclose the emerging panicles, which is the most critical stage for crop productivity.

Damage to the sheaths prevents the panicles from fully emerging. This leads to partial or total panicle failure, resulting in empty, discolored, or malformed grain kernels that significantly reduce harvest yield.

Apart from physical yield loss, the fungus produces toxins that degrade the quality of the grain. This reduces seed vigor, germination rates, and market value of the harvested rice crop.

Disease development is highly dependent on environmental conditions, particularly high humidity and temperatures between 25°C and 30°C. Peak infection occurs during the boot stage of the rice plant.

The pathogen overwinters in infested crop residues and infected seeds. Spores are disseminated by splashing rain, irrigation water, and insect vectors, facilitating the spread across the paddy field.

Early symptoms appear as oblong, brownish, or gray lesions on the leaf sheaths. These lesions expand, often coalescing to cover large areas of the sheath, which eventually may rot entirely.

• Lesion development on leaf sheaths
• Grayish-white fungal growth (mycelium)
• Panicle necrosis and discoloration
• Failure of panicle emergence

A distinctive white powdery fungal growth is typically visible on the surface of the lesions or inside the leaf sheath during periods of high humidity.

Cultural practices are essential, including the use of resistant rice varieties and the destruction of infected crop debris after harvest. Avoiding excessive nitrogen fertilization helps keep the canopy less susceptible.

Chemical control using systemic fungicides is recommended when disease pressure is high. Integrating insecticide applications to control insect vectors, such as rice bugs, is also critical to minimize infection entry points.