Myriangium scale fungus

The causative agent of this disease is the ascomycetous fungus Myriangium duriaei. It is a specialized fungal pathogen that typically thrives on the surface of woody plants. Its biological lifecycle is closely linked to the presence of scale insects (Coccidae), as the fungus often utilizes the honeydew secreted by these pests as a primary nutrient source.

This pathogen primarily infects citrus species, including lemons, oranges, and various pomelo varieties. It is predominantly found in warm, humid climates where agricultural practices allow for the high density of trees, which in turn facilitates the spread of spores and supports the population of associated insect pests.

The characteristic symptoms of Myriangium duriaei infection are black, hard, charcoal-like crusts or galls that form on the bark of twigs and branches. Unlike some other fungi, these formations are quite rigid and persistent. Over time, the affected bark may show signs of tissue necrosis and cracking, which impairs the transport of nutrients within the tree.

Environmental conditions that favor disease development include high humidity, prolonged rainy seasons, and poor orchard ventilation. The fungus spreads via ascospores, which are dispersed by rain splash and wind. Because the fungus thrives in the presence of honeydew-secreting insects, orchards with heavy scale infestations are significantly more susceptible to severe outbreaks of the disease.

The economic impact of the disease is linked to reduced tree vigor, premature leaf drop, and decreased fruit production. Management strategies must be integrated:

• Strict control of scale insect populations using systemic or contact insecticides.
• Pruning of heavily infected branches to restore crown aeration.
• Application of copper-based fungicides during the dormant season to suppress fungal growth.
• Ensuring proper planting distances to promote drying of the canopy.