Onion Purple blotch

Onion Purple blotch: Alternaria porri

  • This disease occurs mainly at the top of the leaves, the infection starts with whitish minute dots on the leaves with irregular chlorotic areas on tip portion of the leaves.
  • Circular to oblong concentric black velvety rings appear in the chlorotic area.
  • The lesions develop towards the base of the leaf.
  • The spots join together and spread quickly to the entire leaf area.
  • The leaves gradually die from the tip downwards.
Identification of pathogen:
  • Alternaria porri mycelium is branched, coloured and septate. Conidiophores arise singly or in groups. They are straight or flexuous, sometimes geniculate.
  • Disease free bulb should be selected for planting
  • Seeds should be treated with Thiram @ 4 g/kg seed.
  • The field should be well drained.
  • Three foliar sprayings with Copper oxychloride 0.25 % or Chlorothalonil 0.2 % or Zineb 0.2 % or Mancozeb 0.2 %
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