Insect damage can increase infection by wounding the plant and allowing fungi to enter. Do not exceed recommended plant densities. Keep soil fertility balanced based on soil tests. All insect controls should be carefully followed as described in HGIC 2205, Insect Pests of Sweet Corn . This disease is caused by the fungus Helminthosporium maydis .
Symptoms occur as leaf spots or cob rots and are fairly easy to recognize on plants.
Spots on the leaves are tan to light brown and occur first on the lower leaves of the plant. Spots often enlarge and increase in number and can cause severe leaf blighting. On the ear the fungus causes oblong, bleached spots which penetrate through the shuck layers and finally into the ear . Rotate corn with nongrass-type plants in the garden. Turn under corn debris soon after harvest to promote rapid decay and destroy overwintering fungi.