Citrus Diplodia

The first signs include wilting of leaves on affected branches, which eventually turn yellow, dry out, and shed. This is often followed by a noticeable decline in branch vigor.

Longitudinal cracks in the bark are common, often accompanied by gummosis, where the tree secretes a gummy substance as a defensive reaction to the infection.

Peeling back the bark reveals dark, necrotic wood beneath. The cambium layer typically shows significant browning and decay, often with a characteristic fermented odor.

In high-humidity environments, small, black, pinhead-sized structures called pycnidia appear on the surface of the bark, indicating active sporulation.

Fruits infected by the fungus exhibit dark, rapidly spreading patches that turn into soft rot, often covered with a dense gray or black fungal mat.

The disease is caused by the fungus Diplodia aurantii (synonym Lasiodiplodia theobromae). This pathogen acts as a facultative parasite, surviving in dead wood and crop debris.

It affects various citrus crops including lemons, oranges, and grapefruits. The fungus typically invades trees through wounds caused by pruning, frost cracking, or insect damage.

The life cycle involves the formation of pycnidia, which produce spores that spread through wind, rain, and insect vectors to initiate new infections.

The pathogen colonizes the inner bark and cambium, effectively disrupting nutrient transport and causing localized dieback within the tree's branches.

It is also a significant post-harvest pathogen, capable of infecting healthy fruits during storage if they come into contact with spore-laden surfaces.

The development of Diplodia is heavily dependent on high humidity and rainfall, which facilitate the germination and spread of fungal spores across the orchard.

Optimal temperatures for the fungus range between +25 and +30°C. Warm, humid summers provide the most dangerous conditions for rapid progression of the disease.

Trees under stress—whether from poor soil nutrition, improper watering, or mechanical injury—are significantly more susceptible to successful colonization by the pathogen.

Overcrowded orchards with poor air circulation retain moisture on bark surfaces, providing a microclimate that strongly favors the establishment of fungal spores.

Neglected maintenance, such as leaving pruning wounds exposed without protective treatments, provides direct entry points for the mycelium to infiltrate the tree.

Citrus Diplodia causes significant economic loss by inducing branch dieback and, in severe cases, the complete death of mature, productive trees.

The disease limits fruit production and lowers fruit quality, causing premature drop and significant waste during the packing and shipping process.

Infected nursery stock can spread the fungus to new plantings, resulting in widespread nursery losses and compromised long-term orchard health.

The persistent nature of the fungus in wood debris means it can remain a constant threat, requiring continuous monitoring and active management efforts.

• Severe reduction in yield
• Death of orchard trees
• High costs for fungicide application
• Losses due to post-harvest decay

Rigorous sanitation is key; all infected branches must be pruned well into the healthy wood, and all tools must be disinfected after use to prevent spread.

Ensuring balanced tree nutrition and appropriate irrigation helps maintain strong tree vigor, allowing the plant to better resist fungal infiltration.

Regular applications of copper-based fungicides after pruning or during the wet season help suppress spore germination on bark surfaces.

Pest management is vital, as insects that damage the bark serve as vectors and create entry wounds, facilitating the initial infection by the fungus.

Post-harvest hygiene, including washing and treating fruit with approved fungicides, is essential to minimize the risk of fruit rot during the supply chain.