Northern corn leaf spot mainly occurs on inbred lines used in seed production. The disease is rarely a problem on hybrids. Symptoms of this disease are sometimes confused with northern corn leaf blight, southern corn leaf blight, and anthracnose.
Symptoms of northern corn leaf spot usually appear at the time of silking or at full maturity. Grayish tan lesions surrounded by a darker border first appear on lower leaf blades. These lesions are narrow and up to 1" long. They may also occur on leaf sheaths and husks. Symptoms vary by race of pathogen and corn genotype. Race 2 produces oblong lesions mainly on lower leaves and on maturing plants that may appear similar to southern corn leaf blight. Race 3 produces narrow, linear lesions on leaves, leaf sheaths, and sometimes husks.
Conditions and Timing that Favor Disease:
This disease is favored by moderate temperatures, humid weather, and minimal tillage.
Northern corn leaf spot is caused by a fungus called Bipolaris zeicola (syn. Helminthosporium carbonum). It overwinters on corn residue. There are several races of this pathogen that can be found in the Corn Belt, but races 2 and 3 appear to be the most common.
Resistance to all races of northern corn leaf spot is available and is therefore it is usually not an important disease in hybrid corn. To manage the disease in susceptible hybrids, use crop rotation and tillage of corn debris where appropriate. Foliar fungicides may be warranted for inbred lines used in hybrid seed corn production.