Thelebolus stercoreus

Thelebolus stercoreus is a species of coprophilous fungus belonging to the Ascomycota division. While it is primarily known for its biological role in decomposing animal waste in natural environments, in agricultural settings—particularly in mushroom cultivation and greenhouse production—it acts as a significant contaminant and nuisance pathogen that disrupts the balanced microbiome of the growing substrate.

The pathogen, Thelebolus stercoreus, thrives in environments rich in nitrogen and organic matter. It is characterized by its ability to rapidly colonize organic substrates that have not been adequately sterilized. Its presence is often an indicator of incomplete composting processes or failures in the pasteurization stage of substrate preparation, making it a common issue in commercial mushroom farming.

The crops most frequently affected include cultivated mushrooms like Agaricus bisporus and various vegetable seedlings grown in heavily enriched peat or manure-based mixes. The fungus does not necessarily attack the plant tissue directly as a parasite, but its aggressive mycelial growth outcompetes the roots for nutrients and water, often causing stunting or localized necrotic lesions on sensitive root structures.

Diagnostic symptoms include the formation of tiny, orange to yellow apothecia (fruiting bodies) dotting the surface of the growing medium. This is typically accompanied by a fuzzy, white mycelial mat that covers the substrate, effectively creating a hydrophobic barrier that limits moisture penetration to the roots. Development is significantly promoted by high relative humidity (above 85%) and temperatures consistently between 20°C and 25°C.

Effective management and prevention strategies include:

• Ensuring complete pasteurization of the growing substrate at appropriate temperatures (usually 60°C for several hours).
• Optimizing greenhouse ventilation to prevent excessive moisture accumulation on the surface.
• Using high-quality, fully aged, and pathogen-free composted organic fertilizers.
• Routine sanitation of equipment and work areas to prevent the spread of fungal spores.