Laurel wilt in Avocado
Background information
Laurel wilt is a destructive vascular disease affecting avocado trees and other members of the Lauraceae family. It is caused by the fungus Raffaelea lauricola, which is symbiotically associated with the redbay ambrosia beetle (Xyleborus glabratus). The beetle, native to Asia, was first detected in the United States in 2002. The disease has since spread, significantly impacting avocado production, especially in Florida.
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Disease development and distribution
The spread of laurel wilt primarily occurs through the movement of the redbay ambrosia beetle. The beetles bore into the wood of host trees, introducing the Raffaelea lauricola fungus. Once inside, the fungus colonizes the tree’s vascular system, leading to blockage and tree death. Infected trees can also spread the disease through root grafting. Laurel wilt has spread rapidly across the southeastern United States, particularly affecting avocado groves in Florida. The movement of infested wood products and beetle vectors continues to pose a threat to other regions.
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Signs and symptoms
Wilted foliage on individual branches; typically with leaves turning reddish or purplish before falling off.Advanced symptoms: Rapid wilting of the entire tree, resulting in brown, desiccated leaves clinging to the branches.Internal symptoms: Dark staining of the sapwood when the bark is peeled back, a sign of the fungal colonization within the vascular system.Other signs: Beetle entry holes, sawdust-like frass near the base of the tree or on the bark, indicating beetle activity.
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Disease Control and management
Monitoring and early detection: Regular scouting of avocado groves for early signs of wilt and beetle activity.Sanitation: Prompt removal and destruction of infected trees to reduce the spread of the fungus and beetles.Chemical control: Use of insecticides to manage beetle populations, although this is often not fully effective due to the beetle’s cryptic lifestyle.Fungicides: Application of systemic fungicides may provide some protection, but it is generally not a long-term solution.Cultural practices: Avoiding the movement of infested wood products and using disease-free planting material.Research and breeding: Ongoing efforts to develop resistant avocado cultivars and improve understanding of the disease dynamics for better management strategies.