Brown Spot or Sesame leaf spot or Helminthosporiose:

Causative agent: Bipolaris oryzae, Helminthosporium oryzae

(Syn: Drechslera oryzae) (Sexual stage: Cochliobolus miyabeanus)

Bengal famine:  1942-1943

Symptoms

• Infected seedlings have small, circular, yellow brown or brown lesions that may girdle the coleoptile and distort primary and secondary leaves.
• Starting at tillering stage, lesions can be observed on the leaves. They are initially small, circular, and dark brown to purple-brown.
• Fully developed lesions are circular to oval with a light brown to gray center, surrounded by a reddish brown margin caused by the toxin produced by the fungi.

Etiology:

• greyish-brown to dark brown septate mycelium
• Conidia are usually curved with a bulge in the centre  and tapering towards the ends.

Favorable Conditions:

• Temperature of 25-300C
• Relative humidity above 80 per cent
• Excess of nitrogen aggravates the disease incidence

Survive and spread:

External seed born disease not soil born

• Survive: infected seed as a primary inoculum infected plant parts, survives on collateral hosts like Digitaria sanguinalis(banso), Leersia hexandra, Echinochloa colonum(sama), Pennisetum typhoides(pearl millet), Setaria italic(foxtail millet) and Cynodon dactylon(dubo).
• Spread : air current

Management:

• Treat seeds with hot water (53−54°C) for 10−12 minutes before planting, to control primary infection at the seedling stage. To increase effectiveness of treatment, pre-soak seeds in cold water for eight hours.
• Grow disease tolerant varieties viz., Bala, BAM 10, IR-20, Jaya, Ratna, Tellahamsa and Kakatiya.
• Treat the seeds with Thiram or Captan at 4 g/kg and with Mancozeb @0.3%
• Use fungicides (e.g., iprodione, propiconazole, azoxystrobin, trifloxystrobin, and carbendazim) as seed treatments.
• Spray the crop in the main field twice with Mancozeb @ 0.2%, once after flowering and second spray at milky stage.