Disease:Brown leaf spot

Bipolaris oryzae (Syn. Drechslera oryzae)- Anamorph (Cochliobolus miyabeanus)- Teleomorph

The disease has been estimated to cause crop loss of 12-43%, 12-30% loss in grain weight and 18-22% loss in filled grains.

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  • Disease 1
  • Disease 2
  • Disease 3
  • Disease 4
  • Disease 5
  • Disease 6
  • Disease 7

Symptoms

  • The symptoms of the disease are found on leaves, glumes , coleoptile, leaf sheaths, and panicle branches and rarely on roots of young seedlings and stems.
  • Typical spots are small, oval or circular in shape and are dark brown or purplish in colour.
  • Fully developed lesions are oval, brown with gray or whitish centre of about 1 cm long.
  • Numerous such spots occurring on leaves cause withering. Glumes also show similar dark brown spots.In such grains, the endosperm turn black in colour.
  • The infected seed on germination show black spots on the coleoptile and cause death of the seedlings (seedling blight).

Procedure for Observation

Select 100 leaves at random from the field. Group the leaves according to the severity of infection based on visual observation. Work out the percentage of leaf area damaged. Rate the damage as < 10 % mild; 10-25 % moderate and >25 % severe.

ETL

  • 10 % area damaged.

    • Control Measures

  • Use healthy seeds collected from disease free plots.
  • Use resistant varieties such as Kanchana, Remya, IR-36 etc.
  • Treating the seeds in hot water at 52oC for 10 minutes is effective. Pre soaking the seed in cold water for 8 hrs increase the effectively of treatment. Treat the seeds with carbendazim (2g/kg seed), copper oxychloride (2-4g/kg seed) or mancozeb (2-4g/kg seed). The seeds can also be treated with Pseudomonas @ 10 g/L of water per kg seed for 12 hours.
  • Foliar spray with Psudomonas /PGPR Mix II @ 20 g/l of water. Spraying can be repeated depending on disease severity.
  • Spray mancozeb(2kg/Ha);Zineb (Zineb 2kg/Ha).
  • Seed infection in the field can be reduced by spraying mancozeb on the crop at heading and grain maturation stage.
  • Good nutrient management based on soil test data.
  • Application of soil amendments such as neem cake can help in reducing disease severity.