Diplodia Gummosis

Diplodia gummosis, caused by the fungus Botryodiplodia theobromae (also known as Diplodia natalensis), is a severe fungal disease that affects the bark and vascular system of woody plants. It is highly notorious among citrus growers for its ability to cause rapid decline and eventual tree mortality.

The disease primarily targets the Citrus genus, including lemon, lime, and orange trees. The pathogen typically enters the host plant through wounds caused by pruning, insects, frost cracks, or mechanical damage, colonizing the wood and spreading through the plant’s internal structures.

The most visible sign of infection is gummosis, where a gummy, sap-like substance exudes from the bark cracks. The bark underneath these lesions often becomes necrotic, darkens, and peels away, revealing discolored wood with a characteristic pungent smell. Foliage symptoms include yellowing (chlorosis) and wilting as the water transport system is impaired.

The development of the disease is favored by high humidity and warm temperatures, which trigger the production of spores within small, black fungal structures called pycnidia. These spores are easily disseminated by wind, splashing rain, and contaminated pruning tools, facilitating rapid spread across an orchard.

Management strategies focus on containment and preventing reinfection:

• Excising infected bark down to healthy tissue and applying copper-based fungicides.
• Sanitizing pruning tools between each tree to prevent cross-contamination.
• Maintaining tree vigor through proper fertilization, irrigation, and drainage to reduce stress.
• Removing and destroying dead or severely infected limbs to eliminate spore sources.

Diplodia gummosis poses a significant economic threat to the citrus industry by reducing the tree's lifespan and productivity. Persistent monitoring and early intervention are essential to protect orchard health, as severe trunk infections are difficult to eradicate once the pathogen has colonized the heartwood.