Northern corn leaf blight

Northern corn leaf blight, caused by the fungal pathogen Exserohilum turcicum, is a significant foliar disease affecting maize crops worldwide. It is characterized by its ability to spread rapidly under favorable environmental conditions, potentially causing severe yield losses in susceptible hybrids.

The host range is primarily limited to corn (maize) and some sorghum species. The fungus survives primarily in crop debris from the previous season, making fields with reduced tillage practices more prone to early outbreaks if host residues are not buried properly.

Symptoms initially appear on lower leaves as small, elliptical, greyish-green spots. As the infection progresses, these lesions enlarge into characteristic cigar-shaped necrotic lesions, which can become grey or tan in color. In severe cases, the entire leaf canopy may appear scorched and necrotic.

Environmental requirements for Exserohilum turcicum development are high relative humidity (above 90%), heavy dew, and moderate temperatures ranging from 18°C to 27°C. Continuous leaf wetness is essential for the fungal conidia to germinate and penetrate the leaf tissue.

The economic impact of this disease is linked to the reduction of photosynthetic area. When lesions cover a large portion of the leaves before the grain-filling stage, the plant suffers from reduced carbohydrate synthesis, leading to stalk rot, lodging, and significant kernel weight reduction.

Effective management strategies rely on an integrated approach:

• planting resistant or tolerant corn hybrids
• crop rotation to break the pathogen's life cycle
• managing crop residues via tillage
• applying foliar fungicides when weather conditions favor disease spread