Southern Sclerotium blight

Southern Sclerotium blight, caused by the basidiomycete fungus Athelia rolfsii (often identified as Sclerotium rolfsii), is a severe soil-borne plant disease. It primarily attacks the stems and roots of plants at the soil line, leading to rapid tissue decay and eventual plant death.

This pathogen is notorious for its extremely broad host range, affecting over 500 plant species worldwide. Agricultural crops such as alfalfa are frequently susceptible to this fungus. Infections in alfalfa can lead to significant thinning of stands, particularly in warmer, humid regions where the pathogen finds optimal conditions to proliferate.

The primary symptom is the appearance of a conspicuous white, fan-like mycelial mat on the stems and surrounding soil. Small, round sclerotia, initially white and turning tan or dark brown, develop within this mycelium. These structures act as the primary survival mechanism for the fungus, allowing it to persist in the soil for several years.

The disease thrives in warm, moist environments, typically requiring temperatures between 25°C and 35°C for rapid infection. Pathogen spread occurs via the movement of infested soil, contaminated water runoff, or the use of infected plant materials. The sclerotia are resilient structures that can withstand various environmental stresses, making them difficult to eradicate once established.

Effective management and prevention strategies include:

• Implementing diverse crop rotation cycles using non-host species like small grains.
• Deep plowing to bury sclerotia at depths that inhibit their germination and survival.
• Improving soil drainage to minimize moisture accumulation around the plant base.
• Applying specific soil fungicides if disease pressure is high in susceptible fields.
• Maintaining field hygiene by controlling weeds and removing infected crop residues.