Head smut of corn and sorghum

Head smut is a significant fungal disease caused by Sporisorium reilianum, which specifically targets maize (corn) and sorghum. As a soil-borne and seed-borne pathogen, it infects the plant during the early seedling stage, systemically invading the host plant until it reaches the flowering phase.

The disease primarily affects the inflorescences of the host plants. Because the fungus is systemic, the infected plant may appear completely healthy throughout its vegetative growth. The presence of the pathogen remains hidden until the plant prepares to produce its reproductive organs, at which point the damage becomes severe and irreversible.

The characteristic symptoms of head smut involve the replacement of flowers and tassels with a mass of black teliospores. In maize, both the ear and the tassel can be entirely replaced by this black, dusty spore mass, often covered in remnants of the host's vascular tissue, which eventually breaks open to release the spores.

Environmental conditions play a critical role in the development of the disease. Sporisorium reilianum thrives in warm soil temperatures, typically between 20°C and 25°C, with moderate moisture levels at the time of germination. Spores can persist in the soil for several years, making crop rotation an essential management strategy.

The economic impact is substantial, as infected plants usually fail to produce any viable grain, leading to significant yield losses. Effective management involves several key practices:

• Utilizing resistant or tolerant corn and sorghum hybrids.
• Treating seeds with effective systemic fungicides before planting.
• Implementing long-term crop rotation to reduce spore concentrations in the soil.
• Sanitation practices, including the rogueing and destruction of infected plants before the spores disperse.