Early leaf spot typically causes brown lesions (spots) on leaves. The spots usually are surrounded by a yellow halo, but sometimes halos are not present. The brown lesion color is most distinct on the lower leaf surface. The fungus produces tufts of silvery, hair-like spores on lesions during humid weather. These spores can be seen on the upper lesion surface with the help of a good magnifying glass.
Although early leaf spot can be found as early as 30 days after planting, it usually is not observed in well-rotated fields until mid-July or later. Spots are first seen on lower leaves. As the disease progresses, the number of spots increases. Plants begin to defoliate, starting with the lower leaves and progressing to the upper canopy. In severe epidemics, plants are completely defoliated. The bare stems may also have lesions.