Northern corn leaf spot of corn
Northern corn leaf spot, also known as Carbonum leaf spot, is caused by the fungus Bipolaris zeicola. It is occasionally seen in the lower canopy during periods of high humidity and moderate temperatures. There are five known races of this fungus. Races 2 and 3 are the most common in the Midwest. Race 2 causes oblong, somewhat rectangular, brown spots (¼ to ½ by 1 inch) on leaves and a black mold on kernels. Race 3 causes long, narrow, light tan lesions (up to 1 inch) that are surrounded by a darker border on leaves, sheaths, and husks. Resistant hybrids and inbreds are available. Crop rotation and tillage reduce inoculum survival. Foliar fungicides labeled for northern corn leaf spot are available.
Gallery Images: G. Ruhl, G. Shaner, A. Robertson, D. Mueller, and C. Grau