Gloeocercospora leaf spot

Systematic position and pathogen type: Gloeocercospora sorghi is a pathogenic fungus belonging to the class Dothideomycetes. It is the primary causal agent of the disease known as Gloeocercospora leaf spot, commonly referred to as zonate leaf spot in some regions due to the appearance of the lesions on infected foliage.

Diseases and host crops: The pathogen primarily affects sorghum species, including grain sorghum, sweet sorghum, and sudangrass. The infection manifests as characteristic leaf spots. These spots initially appear as small, water-soaked areas that later develop into reddish-brown or purple irregular lesions, often exhibiting a zonate or banded pattern as the necrosis progresses.

Biology and life cycle: The fungus survives the winter primarily as sclerotia embedded within infected crop residue remaining in the field. Under favorable conditions during the growing season, these sclerotia germinate to produce conidia. These spores serve as primary inoculum, spreading through wind currents or splashing rain to initiate infection on susceptible leaf tissues.

Developmental conditions and economic impact: High relative humidity, frequent rainfall, and warm temperatures provide ideal conditions for the rapid spread and development of the pathogen. The economic impact is significant as the fungus destroys leaf surface area, thereby reducing photosynthetic efficiency, leading to diminished seed weight, reduced grain quality, and lower biomass production in forage sorghum.

Protection and control measures: Effective management of Gloeocercospora sorghi requires an integrated approach focusing on reducing the initial inoculum and limiting secondary spread:

• Implement strict crop rotation schemes with non-host crops to minimize pathogen survival.
• Utilize deep tillage techniques to bury infected plant debris, which reduces the survival of sclerotia.
• Ensure the use of certified, disease-free seed treated with appropriate fungicides.
• Apply foliar fungicides during the early stages of disease progression if environmental conditions remain favorable for the fungus.
• Select and plant resistant or tolerant sorghum hybrids.