Horse hair blight

Horse hair blight, caused by the fungus Crinipellis sarmentosa, is a notable fungal disease affecting various tropical crops. The disease is named for the distinctive appearance of its mycelium, which consists of dark, thread-like structures that resemble tangled horse hair clinging to the branches and foliage of the host plant.

The primary host of economic importance for this pathogen is cocoa (Theobroma cacao). While the fungus primarily targets the branches, it significantly disrupts the physiological functions of the leaves attached to them. Over time, the fungal threads create a web-like coverage that can encompass large sections of the cocoa canopy, leading to a decline in plant health.

Symptoms of the disease are easily recognizable in the field. Affected branches exhibit thin, black, cord-like rhizomorphs that wrap tightly around the twigs. As the infection progresses, leaves wither and die, but rather than falling to the ground, they often remain suspended by the fungal strands, creating a characteristic blighted appearance that is indicative of a severe infection.

The development and spread of Crinipellis sarmentosa are heavily influenced by the microclimate. The fungus thrives in environments with high humidity, frequent rainfall, and stagnant air. These conditions provide the necessary moisture for the growth of the rhizomorphs and the subsequent production of spores, allowing the disease to move between trees in dense plantations where canopy contact is frequent.

Effective management and control strategies focus on sanitation and canopy structure. Proactive measures include:

• Pruning and removing all infected branches and dead leaves.
• Incinerating or burying infected plant debris to reduce inoculum sources.
• Maintaining proper tree spacing and thinning the canopy to promote airflow and light penetration.