Leaf dieback caused by severe downy mildew (<em>Peronospora destructor</em>)   in an onion bulb crop with secondary colonization of the downy mildew   lesions by the fungus that causes Stemphylium leaf blight (<em>Stemphylium   vesicarium</em>).

Leaf dieback caused by severe downy mildew (Peronospora destructor) in an onion bulb crop with secondary colonization of the downy mildew lesions by the fungus that causes Stemphylium leaf blight (Stemphylium vesicarium).

Photo Source: Lindsey du Toit, Washington State University