Sheath rot

Causative agent: Sarocladium oryzae.

Symptoms:

• 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.

Etiology:

• Whitish, sparsely branched, septate mycelium. 
• Conidia are hyaline, smooth, single celled and cylindrical in shape.

Favorable condition:

• High amounts of nitrogen fertilizer application.
• High relative humidity and temperatures (20−28°C) at heading to mature crop stages.

Survive and spread:

• Seed borne pathogen and air borne conidia
• Survive: Infected seeds and mycelium carried by the rice crop residue.
• Spread: conidia transmitted by insect, wind.

Management:

• Apply potash at tillering stage.
• Apply foliar spray of calcium sulfate and zinc sulfate.
• Apply a seed treatment fungicide like carbendazim,or mancozeb as seed treatment and foliar spraying at booting stage.
• Apply a foliar fungicide like benomyl and copper oxychloride as foliar sprays
• Soil application of gypsum(500 kg/ha) in two splits.
• Application of NeemSeed Kernal Extract (NSKE) 5% or neem oil 3 % First spray at boot leaf stage and second 15 days later.