Sheath Blight
(Rhizoctonia solani)

• 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.
• The presence of several large lesions on a leaf sheath usually causes death of the whole leaf, and 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.
• Five to six week old leaf sheaths 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.
• A yield loss of 25% was reported if the flag leaves are infected.  

• The disease is soilborne
• The fungus produces usually long cells of septate mycelium which are hyaline when young, yellowish brown when old.
• It produces large number of globoses sclerotia, which are initially white, later turn to brown or purplish brown.
•  There are three types of mycelium produced: runner hyphae, lobate hyphae, and monilioid cells.
• Sclerotia consist of compact masses of mycelia. They are irregular, hemispherical, flattened at the bottom, white when young, and turn brown or dark brown when older. Individual sclerotia are 1-6 mm in diameter. They may unite to form a larger mass. Large sclerotia are significantly more virulent than smaller ones.

Favourable conditions

• presence of sclerotia or infection bodies floating on the water
• presence of the disease 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.

• Seed treatment with Pseudomonas fluorescens @ of 10g/kg of seed followed by seedling dip @ of 2.5 kg or products/ha dissolved in 100 litres and dipping for 30 minutes.
• Soil application of P.fluorescens @ of 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 Pseudomonas fluorescens at 0.2% concentration ,commencing from 45 days after transplanting at 10 days interval for 3 times depending upon the intensity of disease.

• Apply FYM 12.5 t/ha or green manure 6.25 t/ha to promote antagonistic microflora
• Avoid excess doses of fertilizers.
• Adopt optimum spacing.
• Eliminate weed hosts.
• Apply organic amendments.
• Avoid flow of irrigation water from infected fields to healthy fields.
• Deep ploughing in summer and burning of stubbles.

• Control of sheath blight has been mainly through the use of foliar fungicides.
• Carbendazim (1 g/lit), Propiconazole (1ml/lit) may be applied.
• Spraying of infected plants with fungicides, such as Benomyl and Iprodione, and antibiotics, such as Validamycin and Polyoxin, is effective against the disease
• Spray Carbendazim 250 g or Chlorothalonil 1 kg or Edifenphos 1 lit/ha.