Corn Leaf Diseases: Northern Leaf Blight

Excerpt from Agronomy Guide for Field Crops (Chapter 3)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Incidence
2. Appearance
3. Disease Cycle
4. Management Strategies
5. Updates on Corn Leaf Diseases: Northern Leaf Blight
6. Related links...

Incidence

Northern leaf blight has traditionally been one of the most damaging corn leaf diseases in Ontario. Use of resistant hybrids has limited yield losses from this disease in commercial corn, however, significant losses continue to occur in seed corn production when highly susceptible corn inbreds are planted.

Appearance

The disease appears as long, elliptical (2-15 cm (1-6 in.)) greyish-green or tan streaks. Lesions most often begin on the lower leaves. As the disease develops, individual lesions may join, forming large blighted areas. In some cases the entire leaves may become blighted or "burned." Losses due to northern leaf blight are most severe when the leaves above the ear are infected at or slightly after pollination. The disease is often confused with Stewart's Wilt.

Plate 26. Northern corn leaf blight showing long elliptical greyish-green or tan streaks.

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Disease Cycle

The fungus survives in corn residue as either spores or fungal strands (mycelium). The spores of the fungus are spread from the ground residue to the developing corn plant through wind or rain "splashing." Although the fungus does overwinter in Ontario, a major source of spores remains the U.S. Midwest corn belt and surrounding Great Lakes states. Plants that become infected act as a secondary source of infection and may spread to other fields. Disease development is favoured by moderate temperatures (18°C-27°C or 64°F-81°F) with prolonged periods of humid or rainy weather.

Management Strategies

Northern leaf blight exists as four races, and most of the commercial corn hybrids have resistance or tolerance to the most common races that occur in Ontario. An increase in northern leaf blight symptoms in an area could indicate the potential for a new race developing and should be reported. Crop rotation and tillage will reduce inoculum levels in surface residues. In reduced tillage systems, rotation and resistance are necessary. Chemical control is not usually economical in field corn.

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Updates on Corn Leaf Diseases: Northern Leaf Blight

• Field Crop Protection Guide - Publication 812
  • Corn: Northern Corn Leaf Blight

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Related links...

• Diseases
• Corn

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