Brown spot of maize

Brown spot of maize is a destructive fungal disease caused by the pathogen Physoderma maydis. It belongs to the group of chytrid fungi and is known for its ability to persist in the soil for long periods. The fungus survives unfavorable conditions by producing thick-walled resting spores, which remain viable in crop debris or soil, serving as a primary source of infection in subsequent seasons.

The pathogen specifically infects maize crops. The infection cycle begins when resting spores are splashed into the whorl of the plant by rainfall or irrigation water. Once in the leaf axils, the spores germinate, releasing motile zoospores that penetrate the leaf tissues, leaf sheaths, or stems, especially in young, actively growing maize plants.

Symptoms initially appear as small yellow-green lesions, which progressively enlarge and turn into dark brown or black spots. A characteristic feature is the yellow halo often surrounding these spots. In severe cases, the lesions coalesce, leading to necrotic bands across the leaves. Stem infection can result in dark, water-soaked, or necrotic areas, which significantly weaken the stalk’s structural integrity.

Environmental conditions play a critical role in disease development. Physoderma maydis thrives in warm, humid climates with temperatures ranging from 23°C to 30°C. High moisture levels are essential for the survival and movement of zoospores. Therefore, fields with poor drainage or areas experiencing frequent, heavy rains during the critical growth stages are most susceptible to outbreaks.

The economic impact of brown spot includes reduced grain yield and poor stalk quality, leading to lodging, which complicates harvesting and increases field losses. Effective integrated pest management strategies are crucial for control:

• Selection of maize hybrids with known field resistance.
• Implementation of crop rotation schedules to reduce pathogen inoculum in the soil.
• Deep tillage to bury infected corn residue.
• Proper water management and field drainage to prevent water accumulation in whorls.