Causative agent: Sarocladium oryzae.
- Sheath rot lesion starts at the uppermost leaf sheath enclosing the young panicles.
- It appears oblong or as irregular spot with dark reddish, brown margins, and gray center or brownish gray throughout.
- Usually several spots are observed and these spots enlarge and combine or grow together and can cover most of the leaf sheath.
- Panicles remain within the sheath or may partially emerge.
- Affected leaf sheaths may have abundant whitish powdery fungal growth (mycelium) visible on the outer surface.
- Panicles that have not emerged rot and the florets turn red-brown to dark brown.
- Sheath rot lesions are sometimes confused with sheath blight lesions. However, sheath rot occurs higher on the plant than sheath blight normally does and interferes with the panicle exsertion. Sheath blight occurs on leaves and lower portions of the plant and will not interfere with panicle exsertion.
- To confirm sheath rot infection, check for:
- lesions developing on the uppermost leaf sheaths that enclose the panicles,
- partially emerged or un-emerged panicles,
- rotting of the sheath,
- development of whitish powdery fungal growth on infected leaf sheaths,
- unexserted panicles.
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