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 [Alternaria porri]
Purple blotch - image 1
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.