Sheath blight

   Causative agent: Rhizoctonia solani (Sexual stage: Thanetophorus cucumeris).

• Affect tillering to heading stage .

Symptoms:

• Initial symptoms are noticed on leaf sheaths near water level.
• On the leaf sheath oval or ellipticalor irregular greenish grey spots are formed.
• As the spots enlarge, the centre becomes greyish white with an irregular blackish brown or purple brown border.
• Sheath blight has symptoms similar to stem rot and stemborer infestation.
• To confirm the cause of disease, check for irregular lesions usually found on the leaf sheaths (initially water-soaked to greenish gray and later becomes grayish white with brown margin).
• Also check for presence of sclerotia.

Etiology:

• Mycelium is white when young but turns yellowish or light brown with age.
• Mycelium produces long multinucleate cells that grow approximately at right angles to the main hypha with a slight constriction at the junction of main hypha and branches

Favorable condition:

• High temperature (28−32°C).
• High levels of nitrogen fertilizer.
• Relative humidity of crop canopy from 85−100%.

Survive and spread:

Survive: Sclerotia and mycelia in infected plant debris.

Spread: runner hyphae through water

Management:

• Drain rice fields relatively early in the cropping season to reduce sheath blight epidemics.
• Use fungicide to treat seeds.
• Apply organic amendments, neemcake @ 150Kg/ha or FYM 12.5 tons/ha.
• Avoid flow of irrigation water from infected fields to healthy fields.
• Deep ploughingin summer and burning of stubbles.
• Spray Carbendazim500 g/ha
• Soil application of fluorescens@ of 2.5 kg/ha after 30 days of transplanting (product should be mixed with 50 kg of FYM/Sand and applied)
• Foliar spray fluorescensat0.2% at boot leaf stage and 10 days later