Northern Corn Leaf Blight (fungus - Exserolilium turcicum): Long, elliptical, tan lesions develop first on older lower leaves. It progresses up the plant and resembles frost or drought injury (photo). Lesions form on husks but ears are not infected. Lesions on resistant hybrids have a yellow margin (photo). It overwinters on leaves, husks, and other plant parts in debris. In wet weather, black spores are produced on the lesions that are wind-blown long distances. Secondary spread is common within and between fields. Moderate temperatures, heavy dews, and frequent showers are favorable. High losses will occur with infection before silking. Infection six weeks after silking will cause minimal loss. Control with resistant hybrids. Check for approved fungicides. Section 18 emergency exemptions for Tilt have been available in the past.
