Northern leaf blight (NLB) is found in areas with a humid climate. It spreads up through the Corn Belt riding hurricane winds, which can quickly carry the organism from south to north. Caused by the fungus Exserohilum turcicum, NLB can overwinter in diseased corn leaves, husks and other plant debris. According to DuPont Pioneer experts, wet conditions experienced in corn-growing areas this year provide favorable conditions for spore production on crop residue.

Spores from NLB are spread by rain splash and air current, landing onto the leaves of new crop plants and infecting the plant. As spores are carried long distances, they can spread infection from plant to plant and field to field. Once spores are deposited, humidity promotes lesion development and multiplication until the leaf is destroyed. Leaf loss affects grain (ear) fill significantly as the leaf is responsible for up-taking carbohydrates for grain development. Infection typically occurs when free water is present on the leaf surface for 6 to 18 hours and temperatures are between 65 and 80 degrees.

Infections begin on lower leaves and progress up the plant, however, in severe NLB breakouts infections may begin in the upper plant canopy. Heavy dews, frequent light showers, high humidity and moderate temperatures favor the spread of NLB. The development of lesions on the ear leaf or above can result in significant yield loss.

Preventative measures can be taken to minimize NLB’s impact on growers’ yields. Pioneer experts recommend selecting resistant hybrids, reducing residue by crop rotation, tillage and applying foliar fungicides as the primary means of controlling NLB. While fungicide application alone may reduce yield losses the most economical control method is selecting resistant hybrids. Pioneer characterizes these hybrids from 1 to 9 based on “leaf loss;” 9 denotes no leaf loss and 1 denotes a 95 percent loss.