- The initial symptoms are formed in the lower leaf sheaths as circular to oblong grey green, water soaked spots at the base of the culms near water level in low land and at ground level in upland rice.
- Under favourable conditions, the infection spreads rapidly, vertically up and horizontally between tillers.
- As the lesions mature, they become straw coloured with dark brown margin and irregular in outline.
- Under moist conditions, cobweb- like white mycelia are produced on lesions, which give rise to white pinhead like sclerotial initials at first, which turn brown on maturity.These sclerotia are easily dislodged from the plant.
- The disease progress is rapid at maximum tillering stage.The disease may also progress to flag leaf and panicle which will prevent the normal emergence and expansion of ears and result in poor filling of grains.
- Field symptom is characterized by the formation of circular dried patches. This will progress with increased disease severity.
Procedure for Observation
Mark 4 one square meter plots in the field at random. Select 5 hills at random from each plot. From this calculate the total number of tillers and the tillers showing the symptoms of sheath blight. Estimate the % infection.
At panicle initiation to booting and flowering and after: 10 % or more tillers affected.
Use tolerant varieties such as Kairali, Kanchana, Aruna, Makom, Onam, Bhagya, Aiswarya, Asha, Remya, Renjini, Arathy, IR-8, Athira and Nila.
Destruction of grasses and weed hosts such as water hyacinth, Echinochloa colona etc on rice bunds and irrigation channels for reduction in saprophytic survival of the organism.
Burn crop residues to reduce the inoculum level.
Land preparation should be done by deep ploughing and exposing the soil and flooding four weeks before transplanting.
Incorporation of soil amendments like green manures along with neem cake helps in increasing beneficial microflora, and also reducing the population of pathogen.
Provide proper spacing with alley ways of 30 cm for every three meter rows to bring down humidity and temperature in the microenvironment and to restrict quick spread of infection between hills.
Balanced application of fertilizer should be given based on soil test result.- 50% more of K in 2 split application offers resistance to rice plants
Seed treatment with chemicals help in controlling seed borne inoculum. The fungicides recommended are: carbendazim 2g/kg seed, ,carboxin 2g/kg seed or hexaconazole 2ml/kg seed.
The disease severity in the field can be reduced by spraying with mancozeb 2kg/Ha, copper oxychloride 2.kg/Ha, carbendazim 500g/Ha etc. Validamycin (Validacin 3L) 500ml/Ha and propiconazole (Tilt) 500ml/Ha are also highly effective in management of sheath blight.
Alternatively spay Pseudomonas/PGPR @ 20g/L of water just before panicle initiation. Repeat the treatment based on severity.
The rice root nematode infestation should be checked in order to reduce the severity of sheath blight in areas where the nematode is prevalent.