Sclerophthora rayssiae var. zeae may sporulate on either side of the lesions and appear downy or woolly. Sporangia disappear as the lesions become necrotic. Oospores occur only in necrotic tissue, in the mesophyll, or beneath the stomata, but not in vascular tissue.
Pathogen causes leaf lesions only (Putnam, 2007). Initially, lesions develop on the leaves as narrow, chlorotic or yellowish stripes, similar to other downy mildews, but only 3-7 mm wide. They have well-defined margins and are delimited by the veins. The stripes later become reddish to purple in some corn genotypes. Lateral development of lesions causes severe striping and blotching. The disease may first be noticed on the lower leaves, which will show the greatest degree of striping; as a result they appear pale-brown and burnt, and severely affected leaves may be shed prematurely.
Seed development may be suppressed, seed may be smaller in size, and the plant may die prematurely if blotching occurs prior to flowering.
Unlike other downy mildews, floral or vegetative parts are not malformed, and the leaves do not shred.