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 %