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Laurel wilt is a fungal disease that attacks the vascular system of woody plants in the Lauraceae family. Once infected, the tree rapidly wilts and dies, often in a matter of weeks. There are currently very few effective control measures beyond sanitation of affected material. A recent study suggests that approximately 300 million redbay trees have died due to the disease as of 2017.

DISEASE SYMPTOMS

  • Flagging of shoots near the apex of the tree
  • Leaves on flagged shoots rapidly brown, but do not abscise from shoots
  • Vascular discoloration

CAUSAL AGENT

The disease is caused by the ascomycete fungus Raffaelea lauricola.

VECTOR

The R. lauricola fungus is symbiont of Xyleborus glabratus, the redbacy ambrosia beetle. This beetle is the primary vector for redbay, swampbay and silkbay trees. It carries the fungus to new trees in specialized mouth parts, and farms R. lauricola for its food. Other ambrosia beetle species are thought to spread R. lauricola in commercial avocado tree groves, which means the disease has multiple vectors within the context of avocado trees, but probably a single vector within the context of eastern forests.

HOST RANGE

  • Woody plants in the Lauraceae, a large family containing over 50 genera and 2500 species, including:
    • Avocado (Persea americana)
    • Redbay (Persea palustris)
    • Swampbay (Persea palustris)
    • Silkbay (Persea humlis)
    • Pondspice (Litsea aestivalis) (POPULATION THREATENED)
    • Pondberry (Lindera melissifolia) (POPULATION ENDANGERED)

GEOGRAPHIC DISTRIBUTION

Since the first detection of the disease in 2003 near the shipping port of Savannah, Georgia, laurel wilt has spread rapidly across the southern United States, and has been reported from 168 counties in nine states as of late 2017. Based on genetic analyses, both Xyleborus glabratus and Raffaelea lauricola were introduced into the United States during a single event, and their populations seem to be native to parts of Asia where they are nonpathogenic.

SPREAD of the PATHOGEN and CONTROL OPTIONS

In Florida, the pathogen is spread by the introduced ambrosia beetle Xyleborus glabratus, which carries the fungus in specialized mouth pouches called mycangia. Other ambrosia beetles in the landscape carry R. lauricola in their mycangia, but may or may not spread the disease to new trees. In addition, the pathogen may spread between neighboring plants that have grafted roots. Rapid detection and destruction of infected plants is the most effective management option for trees in agricultural production. UF researchers are developing methods for exclusion of vectors by pheromones as well as testing efficacy of conventional and organic pesticides. Movement of infested firewood likely spread the vector and pathogen to new states and counties.

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Prepared by Robin Choudhury, UF/IFAS Plant Pathology and EPI.