Fusarium dieback of avocado

The disease is caused by the fungus Graphium euwallaceae, which is symbiotically associated with the polyphagous shot hole borer (PSHB). This fungus acts as the primary pathogen that leads to vascular wilt by colonizing the plant's xylem and disrupting essential water and nutrient flow.

While avocado is the primary commercial crop affected by this pathogen, the fungus has a broad host range, including various forest and ornamental trees. The association between the beetle and the fungus is a specialized biological partnership where the beetle provides a vector for the fungus, which in turn serves as food for the beetle larvae.

Symptoms of the infection manifest as branch dieback, wilting of the foliage, and characteristic dark, necrotic staining around the entry holes made by the beetles. As the fungal infection spreads internally, the tree experiences progressive vascular failure, often leading to total structural collapse if left untreated.

Development and spread are heavily dependent on the movement of the beetle vector and the availability of suitable host trees. Favorable environmental conditions, such as mild temperatures and sufficient moisture, facilitate the activity of the borer, allowing the pathogen to move quickly through plantations.

Management of Graphium euwallaceae is difficult and requires a strict integrated pest management (IPM) approach to minimize damage:

• Strict quarantine regulations for wood movement.
• Sanitation practices involving the removal and deep burial or chipping of infested wood.
• Monitoring of beetle populations using specialized trap systems.
• Development of resistant rootstocks and chemical preventative measures for high-value orchards.