Paddy stem rot / sheath rot (Sclerotium / Sarocladium)

Sheath rot of rice is caused primarily by Sarocladium oryzae. The disease attacks the upper leaf sheath surrounding the developing panicle, restricting panicle exsertion and discolouring grain. Stem rot, caused by Sclerotium oryzae, is a related but distinct disease affecting the lower stem and producing sclerotia that survive in soil.

Identification and symptoms

Sheath rot is diagnosed by brown-grey lesions on the flag leaf sheath that may coalesce and prevent the panicle from emerging fully. Partially emerged panicles carry discoloured, chaffy grains and white powdery fungal growth inside the sheath. Stem rot lesions occur lower on the stem at water level, weakening the culm and causing lodging.

Host crops and life cycle

Sarocladium oryzae is favoured by high humidity, dense canopies and feeding wounds from sheath insects and mites - including panicle mite (Paddy Panicle Mite) - which create entry points. Continuous flooding, excess nitrogen and prolonged dew at booting drive epidemics.

Damage and economic impact

By blocking panicle exsertion and chaffing grain, sheath rot can substantially reduce yield and milling recovery on susceptible lines. Indian field trials report yields up to about 6.07 t/ha at 0.1% propiconazole vs lower yields in untreated controls.

Management

Resistance: resistant or moderately resistant varieties remain the most economic line of control.
Cultural: avoid late and excess nitrogen; widen spacing; rotate with non-host crops in fields with stem-rot sclerotia load.
Chemical: propiconazole 25 EC at 1 ml/L applied at booting through panicle emergence is the recommended foliar treatment. Azoxystrobin 23% SC is an equally effective alternative; mancozeb 0.2% or carbendazim 0.1% are older options. Treatment integrates with the broader boot-stage spray window (Paddy Panicle Stage Management).

References

Sheath Rot (Sarocladium oryzae). TNAU Agritech Portal.
Management of sheath rot Sarocladium oryzae. Pharma Journal.