Exserohilum rostratum

Pathogen and disease type. Exserohilum rostratum is a pathogenic fungus known for causing various types of leaf spot diseases, blights, and seedling rots. As an ascomycete fungus, it spreads primarily through the production of conidia. It is considered a significant threat to agricultural productivity due to its ability to colonize host tissues rapidly under favorable environmental conditions.

Affected crops. This pathogen has a broad host range, particularly among monocotyledonous plants. Key susceptible crops include corn, sorghum, rice, and several types of turfgrass. It can also affect various vegetable species, including tomatoes and onions. Its ability to persist on weed hosts makes it a persistent challenge in integrated crop management systems.

Symptoms and signs. Symptoms typically begin as small, elongated lesions on leaves that may coalesce to form large necrotic areas. These spots often display a tan or straw-colored center surrounded by a dark brown border. In humid environments, a dark, powdery fungal growth may appear on the necrotic lesions, representing the development of reproductive spores.

Development and impact. The development of the disease is favored by warm temperatures, typically ranging from 25°C to 30°C, combined with high humidity or leaf wetness. The fungus spreads easily via wind-blown spores and rain splashes. The economic impact includes significant reduction in photosynthetic capacity, which directly leads to yield loss and reduced quality of harvested grain or produce.

Protection and management. An effective disease management strategy requires combining preventive and curative measures:

• Selecting resistant crop hybrids or varieties.
• Practicing crop rotation to reduce inoculum buildup in the soil.
• Managing crop residues through deep tillage to bury infected plant material.
• Applying systemic fungicides at the early onset of disease symptoms to prevent widespread infection.