Anthracnose stalk rot
Top dieback may occur. Symptoms are similar to those of Fusarium stalk rot except the rot may extend much higher up the stalk. A shiny black color, very characteristic of the disease, appears on the outer stalk. The disease is most prevalent in continuous cropped corn with residue on the surface, especially when the foliar stage of the disease appears earlier in the season. Warm conditions and wet weather favor the disease. Same as for Fusarium stalk rot.
Taken from Corn Production Handbook, KSU Extension
Pest photo source
Diagnosing Corn Problems in Kansas, KSU Extension