Southern corn leaf blight

Southern corn leaf blight, caused by the fungus Bipolaris maydis (formerly Cochliobolus heterostrophus), is a significant fungal disease that primarily affects maize. This pathogen is known for its ability to cause severe foliar lesions, which can lead to significant physiological stress in the crop and impact overall grain production globally.

The host range is primarily centered on maize, including field corn, sweet corn, and popcorn. The fungus survives primarily in infected crop debris on the soil surface, serving as the primary inoculum for the subsequent season. It can also be transmitted via infected seeds, allowing the pathogen to persist even in fields where crop rotation is practiced.

Symptoms typically begin on the lower leaves as small, parallel-sided, tan-colored lesions that gradually expand into elongated, spindle-shaped spots. Under conditions of high humidity, these spots may coalesce, leading to extensive tissue necrosis. A characteristic olive-brown fungal growth often develops on the surface of the lesions as the pathogen produces spores.

The development of the disease is heavily dependent on moisture and temperature. Warm temperatures ranging from 20°C to 30°C, combined with prolonged leaf wetness or high relative humidity, create ideal conditions for spore germination and infection. Wind and rain splash act as the primary mechanisms for dispersing spores within the canopy and across adjacent fields.

• Selection of resistant or tolerant corn hybrids.
• Implementation of crop rotation to break the disease cycle.
• Deep tillage to bury crop debris and promote its decomposition.
• Application of foliar fungicides during peak disease pressure periods.
• Ensuring adequate soil fertility to promote healthy plant vigor.

The economic impact of Southern corn leaf blight is profound, particularly when favorable weather conditions persist throughout the growing season. Severe infestations reduce the photosynthetic capacity of the plant, leading to stunted growth, reduced grain fill, and increased susceptibility to stalk rots. Effective management is essential to minimize yield losses, which can be substantial in highly susceptible varieties.