Laurel wilt

Pathogen and disease type. Laurel wilt is a severe vascular disease caused by the fungus Harringtonia lauricola. By colonizing the water-conducting tissues (xylem) of susceptible trees, the fungus triggers a systemic response that leads to the blockage of nutrient and water flow, effectively causing the host plant to wilt and die within a short timeframe.

Host plants and vectors. The disease primarily affects members of the Lauraceae family, including redbay, sassafras, and commercially important avocado trees. The primary vector is the redbay ambrosia beetle (Xyleborus glabratus). The beetle acts as an invasive agent, carrying the fungal spores into the galleries it bores into the sapwood, establishing the infection directly inside the plant.

Symptoms and signs of infection. Initial symptoms include rapid wilting and discoloration of foliage, which turns reddish-brown or dark purple while remaining attached to the branches. Diagnostic features include:

• Dark, discolored streaks in the xylem layer of stems and trunk cross-sections.
• Small, round entry holes made by ambrosia beetles.
• Fine frass (wood dust) pushed out from the trunk by the beetles.

Conditions for development and impact. The pathogen thrives under warm conditions, which also support the beetle's activity. The lethality rate is extremely high, often reaching 100% for specific susceptible species. In agricultural settings, particularly in avocado groves, the disease causes significant economic loss and remains a major biosecurity challenge for nursery and orchard managers.

Protection and prevention. Currently, there is no cure for an infected tree. Management focuses on sanitation: pruning and destroying infected trees by burning or chipping to eliminate breeding sites for the beetles. Preventing the movement of firewood and wood products from infested areas is crucial. Preventative systemic fungicide injections may protect high-value individual trees but are not feasible for large-scale forest or orchard control.