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Leaf blight - Alternaria sesami
Initially small, circular, reddish brown spots (1-8mm) appear on leaves which enlarge later and cover large area with concentric rings. The lower surface of the spots are greyish brown in colour. In severe blighting defoliation occurs. Dark brown lesions can also be seen on petioles, stem and capsules. Infection of capsules results in premature splitting with shriveled seeds.
The mycelium of the fungus is dull brown and septate and produce large number
of pale grey-yellow conidiophores which are straight or curved. The conidia are light olive coloured with transverse and longitudinal septa. These are around 3-5 septate and conidia are borne in chain over short conidiophore.
Favourable Conditions

  • Low temperature (20-25˚C),
  • High relative humidity
  • Cloudy weather.

Disease Cycle
The fungus is seed-borne and also soil-borne as it remains dormant in the infected plant debris.

  • Treat the seeds with thiram or Carbendazim at 2g/kg.
  • Spray Mancozeb at 2kg/ha or Iprodion 1L/ha.