Northern corn leaf spot caused by the fungus Cochliobolus carbonum has become more prevalent with the greater use of no-till systems.
Although there are several races of the fungus that cause disease, Race 3 most likely causes the greatest impact in New York State.
Northern corn leaf spot is favored by high humidity and warm weather.
Spores can overwinter in crop residue serving as inoculum for subsequent crops.
Airborne spores can be transported long distances from infected fields.
In addition to crop rotations and tillage, the use of resistant hybrids is the most effective control for northern corn leaf spot.
Symptoms of northern corn leaf spot usually appear at the time of silking or at full maturity.
Symptoms of northern leaf spot consist of circular tan to brown lesions (1/8 to ½ inch) running in a line along the leaf vein. These lesions are often described as looking like a "string of pearls."
- Northern Corn Leaf Spot Fact Sheet (PDF)