Sheath Rot:Sarocladium oryzae
- 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.
- 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.
- 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)
- 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.
- TamilNadu Agritech Poratal