Northern corn leaf blight
Northern corn leaf blight is caused by the fungus Exserohilum turcicum, also known as Setosphaeria turcica, and previously known as Helminthosporium turcicum. The disease organism overwinters as mycelia and conidia 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.