Horsehair blight

Horsehair blight is a fungal disease caused by the basidiomycete Marasmius crinisequi. This pathogen is known for its unique vegetative structure, producing thin, dark, wire-like rhizomorphs that firmly adhere to the stems and leaves of host plants, giving the appearance of tangled horsehair.

The disease primarily impacts woody plants in humid tropical and subtropical environments. Major hosts include significant agricultural crops such as tea (Camellia sinensis), coffee, and cocoa. It can also occur on various ornamental shrubs when climatic conditions are favorable for fungal proliferation.

The primary symptom is the presence of black, thread-like mycelial strands extending across the surface of the plant canopy. As the infection progresses, affected leaves die and turn necrotic, but they remain suspended in the web of rhizomorphs, causing significant aesthetic and physiological damage to the plant.

The development of the pathogen is highly dependent on environmental moisture. High humidity and prolonged leaf wetness are essential for the survival and spread of the rhizomorphs. The disease is most prevalent in poorly managed, dense plantations with limited air movement between individual plants.

Management strategies emphasize the reduction of humidity within the plant canopy and physical removal of infected tissue. Pruning practices are essential to improve air circulation, while the application of copper-based fungicides serves as a preventative measure to limit the spread of Marasmius crinisequi.