Look for the protruding hilum at the base of the spores. Exserohilum turcicum - formerly Helminthosporium turcicum. Long elliptical lesions that are reasonably easy to recognize. Can be confused with Stewart's wilt , but Stewart's wilt lesions have irregular, wavy margins. Kabatiella zeae .
Lesions appear water-soaked on the underside.
Often confused with genetic spots . Spores not visible with a dissecting scope. Erwinia stewartii . Linear lesions turning from pale-green to yellow to brown. Margins - wavy or irregular.