Southern corn rust

The causal agent of this disease is Puccinia polysora, an obligate biotroph fungus belonging to the order Pucciniales. It is a highly aggressive pathogen that relies entirely on living host tissue to complete its life cycle, utilizing wind-borne spores to spread across large geographical areas.

Southern corn rust primarily affects maize (Zea mays). Under high disease pressure, it can cause severe damage to commercial fields, specifically during the reproductive growth stages of the plant, potentially leading to significant yield losses in corn production worldwide.

The primary symptom is the development of numerous, small, circular-to-oval pustules, known as uredinia, which are golden-brown in color. These pustules appear predominantly on the leaf surfaces, often in high density. As the infection progresses, these pustules rupture the leaf epidermis, releasing thousands of spores and leaving the leaf appearing chlorotic and blighted.

The fungus thrives in warm and humid environments. Specifically, temperatures between 23 °C and 30 °C, combined with high relative humidity or prolonged leaf wetness, trigger rapid spore germination and infection cycles. These climatic conditions often lead to explosive disease development in susceptible maize hybrids.

The impact of the disease is significant, as it reduces the plant's photosynthetic capacity, causing premature senescence and poor grain fill. Management strategies include the cultivation of resistant or tolerant corn hybrids, field monitoring for early pustule detection, and the judicious application of triazole or strobilurin-based fungicides to protect the crop during critical growth phases.

• Application of systemic fungicides at the early onset of infection.
• Selection of genetically resistant maize hybrids.
• Crop rotation to reduce primary inoculum levels.
• Field scouting during high humidity periods.