Sheath Blight

Symptoms :

• The fungus affects the crop from tillering to heading stage.
• Initial symptoms are noticed on leaf sheaths near water level.
• On the leaf sheath oval or elliptical or irregular greenish grey spots are formed.
• As the spots enlarge, the centre becomes greyish white with an irregular blackish brown or purple brown border.
• Lesions on the upper parts of plants extend rapidly coalesing with each other to cover entire tillers from the water line to the flag leaf.
• In severe cases all the leaves of a plant may be blighted in this way.
• The infection extends to the inner sheaths resulting in death of the entire plant.
• Older plants are highly susceptible.
• Plants heavily infected in the early heading and grain filling growth stages produce poorly filled grain, especially in the lower part of the panicle..

Pathogen

• The fungus produces septate mycelium which are hyaline when young, yellowish brown when old.
• It produces large number of spherical brown sclerotia.

Favourable conditions :

• Presence of sclerotia or infection bodies floating on the water
• Presence of the sclerotia in the soil
• Relative humidity from 96 to 100%
• Temperature from 28-32 °c
• High levels of nitrogen fertilizer
• High seeding rate or closing plant spacing
• Frequent rain

Mode of Spread and Survival

• The pathogen can survive as sclerotia or mycelium in dry soil for about 20 months but for 5-8 months in moist soil.
• Sclerotia spread through irrigation water.
• The fungus has a wide host range.
• The presence of several large lesions on a leaf sheath usually causes death of the whole leaf, In severe cases all the leaves of a plant may be blighted in this way. The infection extends to the inner sheaths resulting in death of the entire plant. Older plants are highly susceptible. Plants heavily infected in the early heading and grain filling growth stages produce poorly filled grain, especially in the lower part of the panicle.. Pathogen The fungus produces septate mycelium which are hyaline when young, yellowish brown when old. It produces large number of spherical brown sclerotia. Favourable conditions : Presence of sclerotia or infection bodies floating on the water Presence of the sclerotia in the soil Relative humidity from 96 to 100% Temperature from 28-32 °c High levels of nitrogen fertilizer High seeding rate or closing plant spacing Frequent rain Brown Elongated Lesions on Sheaths near Water Level Mode of Spread and Survival The pathogen can survive as sclerotia or mycelium in dry soil for about 20 months but for 5-8 months in moist soil. Sclerotia spread through irrigation water. The fungus has a wide host range.

Management:

• Grow moderately resistant varieties viz.,ADT 56, ADT 57, ADT 59 and KKM 1.
• Apply organic amendments viz., neem cake @ 60Kg/ac or FYM 5 tonnes/ha.
• Avoid flow of irrigation water from infected fields to healthy fields. .
• Deep ploughing in summer and burning of stubbles.
• Spray Carbendazim 100 g /ac. Soil application of B. subtilis @ of 1 kg/ac after 30 days of transplanting. (The product should be mixed with 20 kg of FYM/Sand and applied). Foliar spray at 0.2% at boot leaf stage and 10 days later.(400 g/ac).
• Soil application of B. subtilis (TNAU) @ of 1 kg/ac after 30 days of transplanting (The product should be mixed with 20 kg of FYM/Sand and applied). Foliar spray at 0.2% at boot leaf stage and 10 days later.(400 g/ac).

Source of information:

• AICRIP rice, TNAU, Coimbatore Rice diseases- online resource, IRRI, Phillippines.

• IRRI, Phillippines

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