Marasmiellus scandens

Marasmiellus scandens is a pathogenic fungus responsible for a condition widely known as white thread blight or spider web disease. This basidiomycete fungus is characterized by the production of delicate, white, string-like mycelial strands that spread across the surface of stems and leaves, eventually forming a web-like network that restricts plant development.

The primary hosts for this pathogen include various woody tropical plants, with cocoa (Theobroma cacao), coffee, and rubber trees being the most economically significant. In regions with constant high humidity and consistent temperatures, this fungus can become a persistent threat, causing chronic damage to plantations throughout the year.

Initial diagnostic symptoms include the appearance of small, white fungal mycelia that look like thin threads wrapped around twigs and leaf stalks. As the infection progresses, the fungal web becomes denser, leading to the necrosis of the underlying tissue. Infected leaves typically turn yellow or brown, wither, and eventually drop off, significantly reducing the tree's photosynthetic capacity.

The development of this disease is highly dependent on environmental humidity and lack of airflow. Spores are primarily dispersed through rain splash and wind, allowing the infection to jump from branch to branch or between neighboring trees. Shaded, dense canopies create the ideal microclimate for the fungus to thrive and reproduce rapidly, especially during peak rainy seasons.

The economic impact of Marasmiellus scandens is linked to reduced fruit yield and long-term tree decline caused by excessive leaf loss and shoot death. Effective management and control strategies are essential to minimize losses:

• Regular pruning of infected branches to remove the inoculum source.
• Canopy thinning to increase light penetration and improve air circulation.
• Application of copper-based fungicides during the wet season to protect susceptible tissue.
• Maintaining good plantation hygiene by removing dead plant debris from the ground.