Sheath Blight:Rhizoctonia solani
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 coalescing 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 the 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 the 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.
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.
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
Identification of pathogen:
- The disease is soil-borne
- The fungus produces usually long cells of septate mycelium which are hyaline when young, yellowish brown when old.
- It produces a large number of globose 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.
Management:
Cultural methods
- 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.
Chemical methods:
- Apply Neem cake at 150 kg/ha
- Foliar spray with Neem oil at 3% (15 lit /ha) starting from disease appearance.
- Soil application of P. fluorescens talc based formulation at 30 DAT @ 2.5 Kg/ha and foliar spray (0.2%) at boot leaf and 10 days later @ 1 Kg/ha.
- 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)
- Foliar spray with TNAU Pf 1liquid formulation @ 5ml/lit
- Control of sheath blight has been mainly through the use of foliar fungicides.
- Spraying of Carbendazim 50 WP @ 500g/ha or Azoxystrobin @ 500ml/ha or
- Hexaconazole 75% WG @ 100mg/ lit 1st spray at the time of disease appearance and 2nd spray 15 days later (or)
- Spraying of infected plants with fungicides, such as Benomyl or Iprodione or antibiotics, such as Validamycin and Polyoxin is effective against the disease
Source-
- TamilNadu Agritech Portal
