Stachybotrys theobromae

Causal agent and disease type. The disease is caused by the fungus Stachybotrys theobromae, which acts as a necrotrophic pathogen. It is a fungal infection that specifically targets the woody tissues of its host. The fungus thrives by colonizing the bark and cambium layers, interfering with the plant's essential vascular functions.

Affected crops and economic impact. The primary host of this pathogen is the cocoa tree (Theobroma cacao). The damage is significant, as it can kill branches and eventually entire trees. Economic impact includes reduced pod production, increased costs for plantation maintenance, and long-term loss of tree longevity, which directly threatens cocoa supply chains.

Symptoms and signs. The disease manifests as localized infections on the bark, characterized by dark, often black fungal growth. Key diagnostic signs include:

• Dark necrotic patches on the branches or stems.
• Wilting and yellowing of foliage distal to the infection point.
• Cracking of the bark as the underlying tissues die.
• Progressive dieback of branches leading to complete branch loss.

Conditions for development. Stachybotrys theobromae requires high humidity and warm temperatures to thrive and produce spores. The pathogen is most active during wet periods. It typically enters the tree through wounds caused by pruning, insect damage, or environmental stressors such as sunscald, which weaken the bark's natural barrier.

Protection and prevention measures. The most effective management approach is sanitation. Pruning out infected branches and removing dead wood is critical to reducing spore inoculum. Farmers should ensure proper spacing between trees to improve airflow and reduce humidity levels. In severe cases, protective fungicide applications and maintaining overall tree vigor through fertilization are recommended.