Diaporthe canker of eucalyptus

The disease is caused by the ascomycete fungus Diaporthe lusitanicae, a well-known pathogen within the Diaporthaceae family. This fungus is specifically adapted to infect woody tissues, primarily targeting various species of eucalyptus. It acts as a opportunistic parasite that can thrive in both natural forests and commercial plantations.

The primary host range includes different eucalyptus species (Eucalyptus spp.). The fungus targets the bark and the underlying cambium layer, which are vital for the tree's transport of water and nutrients. When the pathogen successfully colonizes the host, it causes systemic stress that often leads to the decline of the tree's health.

Symptoms are characterized by the development of localized bark necrosis, which often progresses into sunken cankers. These lesions disrupt the flow of sap, leading to wilting, yellowing of the foliage, and dieback of distal branches. The presence of small, black, pinhead-sized pycnidia erupting through the bark surface is a diagnostic feature used to identify the fungal presence.

Environmental conditions play a critical role in the epidemiology of Diaporthe lusitanicae. The fungus thrives in warm, humid climates where moisture persists on plant surfaces, facilitating spore germination and entry into the host. Spread is mainly driven by rain splash and wind-borne dispersal of conidia, often exacerbated by insect activity that creates wounds for infection.

The economic impact of the disease is significant, as it leads to reduced growth rates, branch death, and in severe cases, the mortality of the entire tree. Effective management strategies focus on integrated approaches:

• regular inspection and removal of infected branches;
• minimizing tree stress through proper spacing and water management;
• application of protective fungicides in nursery settings;
• selecting disease-resistant eucalyptus clones for future planting.