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    Purple blotch [Alternaria porri]

    Purple blotch has been causing serious problems in leek crops in the last few years. The critical point here is that it is not always recognized as a fungal disease.


    Purple blotch - image 1

    Purple blotch - image 1

    Pest Profile

    • Symptoms & Diagnosis


      Leeks are most often infected, but onions and garlic can also be infected. The fungus thrives under warm and hot conditions, and therefore represents a danger mainly in crops grown in greenhouses or under other forms of protection.

      Pattern of damage

      Oval-shaped greyish-brown to black spots with a purple edge are visible on the plant leaves (Picture 1). After a certain period of time, the leaves become twisted and dry up.



      A crop rotation of at least 3 years is recommended to prevent the occurrence of purple blotch.