The northern corn leaf blight organism overwinters in
diseased corn leaves, husks and other plant parts. Spores are
produced on this crop residue when environmental conditions
become favorable in spring and early summer. These spores are
spread by rain splash and air currents to the leaves of new crop
plants where primary infections are produced. Infection occurs
when free water is present on the leaf surface for 6 to 18 hours
and temperatures are 65 to 80° F.