Sorghum cercospora leaf spot

The disease is caused by the fungus Cercospora sorghi, which belongs to the class of imperfect fungi. This pathogen primarily affects the foliage of sorghum plants, surviving the off-season on infected crop debris and in the soil. The fungus spreads through the production of conidia, which are disseminated by wind and splashing raindrops during the growing season.

Sorghum cultivars, including grain sorghum, forage sorghum, and sudangrass, are susceptible to this pathogen. The infection is prevalent in areas with warm, humid climates where extended periods of leaf wetness occur. These conditions allow the fungus to complete multiple life cycles during a single growing season, significantly increasing the inoculum density.

Symptoms initially appear as small, elongated, or rectangular spots on the leaves, typically ranging from reddish-brown to dark purple in color. As the infection progresses, the lesions enlarge, often becoming necrotic. The centers of the spots may turn gray or light brown, surrounded by a distinct dark border, and when infections are severe, these lesions coalesce to kill large portions of the leaf tissue.

The development of the disease is heavily favored by high humidity (80% and above) and temperatures between 20°C and 30°C. Dense plant populations that restrict airflow, coupled with frequent rainfall or heavy dew, create an ideal environment for the conidia to germinate and colonize healthy leaf tissue rapidly, leading to secondary spread throughout the field.

The economic impact of Cercospora sorghi is due to the loss of photosynthetic leaf area, which limits the plant's ability to fill grain and store biomass. Severe defoliation reduces both yield and forage quality. Effective management requires an integrated approach to minimize the impact of the disease:

• Planting resistant or tolerant sorghum hybrids.
• Implementing crop rotation with non-host crops to break the disease cycle.
• Incorporating or removing crop residues to reduce the primary inoculum source.
• Maintaining optimal plant density to ensure good field aeration.
• Applying recommended fungicides if weather conditions are conducive to disease outbreaks.