Northern Corn Leaf Spot
Symptoms:
- Lesions are generally oval to circular tan spots
- The five different races of this pathogen can cause different symptoms
- Race 1 causes oval to circular, tan lesions that are 1.2 x 2.5 cm in size on leaves. Rings of spores may be present within lesions
- Race 2 causes oblong, brown spots on leaves, which are 0.5 x 2.5 cm in size
- Races 3 and 4 will produce narrow, long, gray or tan lesions with a border on leaves, sheaths, and husks, which are (.5 -2 x 15-20 mm) in size. However, the lesions may vary with different corn genotypes. Race 4 may also have concentric rings of spores within lesions
- Race 0 causes only small flecks or spots on leaves
- Northern corn leaf spot lesions can be confused with lesions produced by northern corn leaf blight, southern corn leaf blight, and anthracnose
Pathogen Involved:
- Cochiobolus carbonum (= Bipolaris zeicola) (a fungus)
- This pathogen overwinters on residue of corn
- Generally, race 2, 3, and 4 cause important diseases of seed corn production
- Race 1, 2, 3, and 4 may be found in the corn belt
- Race 1 is not considered to be a threat.
Time of Occurrence:
- Lesions usually occur on lower leaves at the time of silking or at full maturity
- Some races may cause small lesions early in the growing season
Conditions Favoring Disease:
- Most severe in warm and humid weather
Disease Management:
- Generally, this is not an important disease of hybrid corn
- Resistance to all races of northern corn leaf spot is available
- Crop rotation
- Tillage of corn debris at the end of the growing season where appropriate
- This disease should often be controlled on inbred lines and foliar fungicides may be warranted for hybrid seed corn production