First symptoms are small irregular shaped, water-soaked lesions often near leaf edges.
These quickly develop into large, dark brown to black irregular lesions that are not limited by leaf veins, as is early blight. Late blight lesions don't have the tight target look that lesions of early blight do. When conditions are right, the fungus will sporulate, and a thin, white mildew will occur on the underside of the leaf. At times, these spores will only occur on the margins of the lesions. The lesions can have a very distinct yellow halo around them.