Sheath Rot

• Discoloration in the flag leaf sheath
• Rotting occurs on the leaf sheath that encloses the young panicles.
• Irregular spots or lesions, with dark reddish brown margins and grey centre, discoloration in the sheath, lesions enlarge and often coalesce and may cover the entire leaf sheath
• Severe infection causes entire or parts of young panicles to remain within the sheath
• Unemerged panicles rot and florets turn red-brown to dark brown
• Whitish powdery growth inside the affected sheaths and young panicles, infected panicles and grains are sterile, shriveled, partially or unfilled and discoloured.
• The disease is important during the heading towards the maturity stages of the rice crop.
• Some panicles do not emerge or emerge partially.
• Favourable conditions: High amount of nitrogen, high relative humidity, and dense crop growth favours sheath rot development. The fungus grows best at 20 to 28°C.

Identification of pathogen:

• The fungus produces white mycelium, sparsely branched, septate, and measures 1.5-2m in diameter.
• Conidiophores arising from the mycelium are slightly thicker than the vegetative hyphae, branched once or twice, each time with 3-4 branches in a whorl.
• The ultimate branches are phialides and produce conidia that are cylindrical to slightly fusiform, often somewhat curved, hyaline, smooth, single-celled, 4-9 x 1-2.5 m.
• In some cases, the fungus infects the sheath in combination with bacterial pathogens attacking the sheath and causing grain discoloration (e.g., Pseudomonas fuscovaginae).
• The fungus invades rice through the plant’s stomates and wounds and grows intercellularly in the vascular bundles and mesophyll tissues.
• The sheath rot fungus survives as a mycelium in infected residue and on seeds.

Management:

Cultural methods:

• Removal of infected stubbles after harvest
• Optimum plant spacing can reduce the disease.
• Application of potash at tillering stage is also recommended.
• Control weeds and  keep field sanitation.

Preventive method

• Bacterization with Pseudomonas fluorescens reduced sheath rot severity by 20-42%, enhanced crop growth and increased grain yield.
• Seed treatment with P.  fluorescens @ of 10g/kg of seed followed by seedling dip @ of 2.5 kg products dissolved in 100 litres and dipping the seedlings of 20 percent for 30 minutes.
• Soil application of P. fluorescens @  2.5 kg/ha after 30 days of transplanting (This product should be mixed with 50 kg of FYM/Sand and then applied)
• Foliar spray of P. fluorescens  at 0.2% concentration, commencing from 45 days after transplanting at 10 days interval for 3 times depending upon the intensity of the disease.
• Seed treatment with TNAU Pf 1liquid formulation @ 10 ml/kg of seeds
• Seedling root dipping with TNAU Pf 1liquid formulation (500 ml for one-hectare seedlings)

Chemical methods:

• Apply Gypsum @ 500 kg/ha at two equal splits once basally and another at the active tillering stage.
• Neem oil 3% or Ipomoea leaf powder extract (25 kg/ha) or Prosopis leaf powder extract (25 kg/ha). First, spray at boot leaf stage and second 15 days later
• Seed treatment with fungicides such as Mancozeb and Benomyl effectively eliminate seed borne inoculums (or)
• Hexaconazole 75% WG @ 100 mg/ lit 1st spray at the time of disease appearance and 2nd spray 15 days later (or)
• Application of a systemic fungicide Tridemorph and insecticide, phosphamidon in combination protected the plants from sheath rot (or)
• At booting stage, foliar spraying with carbendazim @ 500g/ha or edifenphos or mancozeb or Chlorothalonil or Metominostrobin @ 500 ml/ha was found to reduce sheath rot (or)
• Foliar spraying with Benomyl and copper oxychloride were also found to be effective.