Mal secco

Mal secco is a highly destructive fungal disease of citrus, caused by the phytopathogen Phoma tracheiphila. Belonging to the class Deuteromycetes, this fungus primarily invades the vascular system of the host plant, leading to significant economic losses in citrus-producing regions.

The disease primarily targets lemons, citrons, and some varieties of oranges. The hallmark symptom is the progressive drying of branches, known as "dry disease." Internally, the wood of infected branches displays a distinctive salmon-orange or brick-red discoloration, which results from the fungal invasion of xylem vessels.

The biology of the pathogen involves penetration through wounds, pruning cuts, or leaf scars. Once inside, the fungus colonizes the xylem tissue, producing toxins that clog the water-conducting vessels. This vascular blockage prevents the upward movement of water, causing the foliage to wilt and the affected branches to die back.

Disease development and spread are favored by moderate temperatures (20–25°C) and high humidity, especially when accompanied by rainfall. The pathogen releases conidia that are disseminated via wind, rain splashes, and human activities, such as contaminated pruning tools, allowing the fungus to spread rapidly within orchards.

Due to its high virulence, managing mal secco is challenging and requires strict adherence to control measures:

• cultivating resistant rootstocks and citrus varieties;
• strict sanitation by pruning and destroying infected branches;
• frequent disinfection of pruning tools;
• preventive application of copper-based fungicides;
• imposing strict quarantine regulations to prevent the movement of contaminated material.