Spread within a field is primarily caused by splashing water. High rainfall and warm temperatures favor rapid disease development. Leaf Blight Symptoms. Leaf blight, caused by the fungus Dendrophoma obscurans, is easily confused with common leaf spot. In time, the spots become targetlike with a dark brown center surrounded by a lighter brown zone and a purple, red, or yellow margin, which blends into the healthy green tissue.
Older lesions are usually V-shaped with the widest part at the leaf edge.
Persistence And Transmission. Leaf blight develops best in warm, wet weather but may become severe at any time of year. Spores are produced under favorable conditions and are blown or splashed to other surrounding leaves or plants where new infections take place. Leaf Scorch Symptoms. Leaf scorch or red spot, caused by the fungus Diplocarpon earliana, first appears on the upper leaves of infected plants.