Northern Corn Leaf Blight is caused by the fungus Exserohilum turcicum. It survives over winter in infected corn debris and produces spores that spread by wind and splashing water. Cool, humid weather and prolonged leaf wetness favour infection. The characteristic long, cigar-shaped lesions usually begin on lower leaves and move upward. When infection occurs early, particularly before silking, extensive leaf loss can reduce the plant's ability to produce a good crop. Later infections are usually less damaging.

How to Fix It
Choose resistant varieties: Resistant sweet-corn varieties are one of the most effective ways to manage Northern Corn Leaf Blight.
Crop rotation: Avoid planting corn in the same location year after year. A three-year rotation away from corn helps reduce inoculum surviving in crop debris.
Clean up corn debris: Remove or thoroughly incorporate infected stalks and leaves after harvest so they decompose.
Keep leaves dry: Water at soil level when possible. If overhead irrigation is necessary, water around midday so foliage dries quickly.
Give plants good airflow: Avoid unnecessarily dense planting that keeps foliage damp for long periods.