The fungus overwinters in crop residue and produces spores which can be carried for long distances by wind. This disease is found in most sweet corn fields, yet is seldom severe enough to cause economic loss. Spots produced are larger than those caused by the southern corn leafspot fungus. Spots are from one to six inches long and one-half to one inch wide. With maturity, the center of the spot has a dark brown color.
Infection occurs first on older foliage.
High humidity and temperatures between 60 to 80 degrees F favor disease development. Varieties vary in their reaction to the fungus. The fungus causing this disease occurs in most fields but seldom does economic damage. Infection requires high temperatures and presence of surface moisture. The first symptom of the disease is small circular spots.