Sorghum ergot

The fungal life cycle begins with the germination of sclerotia in the soil, which produce spores that are disseminated by wind or insects to the plant stigmas.

The fungus colonizes the ovary and replaces the developing seed with its own mycelium, eventually forming dark, hard, horn-shaped structures known as sclerotia.

These sclerotia can survive in the soil for significant periods, serving as the primary source of inoculum for subsequent growing seasons if conditions are right.

The biological nature of Claviceps sorghi makes it highly adapted to the infection of flowering grasses, especially when environmental conditions are conducive to fungal growth.

The primary symptom of sorghum ergot is the production of honeydew, a sticky, sugary exudate that leaks from the infected spikelets during the anthesis phase.

This sticky substance is rich in fungal conidia and attracts various insects, which act as vectors, spreading the spores throughout the sorghum field.

As the disease progresses, dark brown to black sclerotia emerge from the florets, becoming clearly visible as they replace the normal grain structure.

The panicle appears dirty and sticky due to the honeydew, and secondary colonization by other fungi may cause the exudate to turn gray or black.

Visual inspections during the flowering and grain-filling stages are critical, as the presence of honeydew and developing sclerotia are definitive signs of infection.

Sorghum ergot development is strongly favored by cool to moderate temperatures and high relative humidity, particularly during the flowering period of the host plant.

Extended periods of rainfall or heavy morning dew provide the necessary moisture for the germination of spores and the formation of honeydew.

Staggered flowering times within a field can increase the risk of infection, as the crop remains vulnerable to the pathogen for a longer duration.

Proximity to wild grass species that are also susceptible to Claviceps species creates an ongoing reservoir for the pathogen to spread into commercial fields.

High planting densities combined with poor field ventilation can create a microclimate that effectively traps moisture and promotes fungal proliferation.

The economic impact of sorghum ergot is primarily due to direct yield losses, as infected ovaries fail to produce grain, resulting in lower total weight per panicle.

Contamination of harvested grain with sclerotia poses a major safety risk, as these structures contain toxic alkaloids that are harmful to both humans and livestock.

The disease complicates post-harvest processing, requiring expensive cleaning and sorting equipment to remove sclerotia and ensure the grain meets quality standards.

In cases of severe infestation, the grain might be rejected entirely by processors, leading to significant financial losses for the grower.

Ergot infections can also reduce the seed quality, impacting germination rates and seedling vigor if the infected grain is accidentally used for planting purposes.

Integrated management is essential, starting with the use of high-quality, certified seeds that have been thoroughly cleaned of any sclerotia.

Implementing a crop rotation scheme of at least three years between sorghum plantings helps reduce the population of sclerotia in the soil.

• Deep plowing to bury infested crop residues.
• Control of susceptible grassy weeds in and around fields.
• Selection of hybrids with uniform and rapid flowering characteristics.
• Strict field hygiene to prevent the spread of fungal spores.
• Use of fungicides when conditions are high-risk during flowering.

Regular field scouting during the flowering window is necessary to identify early symptoms and take immediate action to manage the spread of the disease.

Optimal crop management practices, including balanced fertilization and precise irrigation, help ensure a uniform crop stand that is more resilient to environmental stress.