Laurel wilt is a destructive disease caused by a fungal pathogen (Raffaelea lauricola) that is carried into trees by the non-native Redbay ambrosia beetle (Xyleborus glabratus).
Redbay ambrosia beetle (Xyleborus glabratus).
Photo credit: Joseph Benzel, Screening Aids, USDA APHIS PPQ, Bugwood.org
Both beetle and fungus are native to southern Asia. Laurel wilt is a “vascular wilt disease” and impacts the sapwood (xylem), which transports water through the tree. As the pathogen impacts the tree’s xylem cells, water flow is restricted, which leads to wilting and eventual mortality. Ambrosia beetles are sometimes referred to as “fungus farmers” because they carry fungal spores on or in their bodies. As the female redbay ambrosia beetle bores into the host plant, she inoculates the tree with R. lauricola and cultivates the fungus for her offspring to feed on.
This disease impacts several trees in the family Lauraceae, including redbay, sassafras, spicebush, pondspice, swamp bay, bay laurel, and avocado. Since its initial detection in northern Georgia in 2002, laurel wilt disease has spread to eleven states across the southeast and caused extensive mortality.
Distribution of counties with laurel wilt disease by year of initial detection (as of March 10, 2021).
USDA Forest Service, Public Domain.
In some cases, laurel wilt disease was detected in isolated counties away from the primary distribution. These instances are likely a result of infested firewood being transported across state and county lines.
Infected trees generally die within months, often showing a full crown of dead, brown leaves.
Redbay trees with dead, brown leaves as a result of laurel wilt diesease (Raffaelea lauricola).
Photo credit: Ronald F. Billings, Texas A&M Forest Service , Bugwood.org
Other symptoms include stunted foliage and dark vascular staining when the bark is removed.
Vascular staining as a result of laurel wilt diesease (Raffaelea lauricola).
Photo credit: Ronald F. Billings, Texas A&M Forest Service , Bugwood.org
You may also see signs of ambrosia beetles on symptomatic trees, like sawdust “toothpicks” protruding from beetle entrance holes. There is no cure once a tree has this disease. Management options are limited, and the best way to prevent the spread of laurel wilt is to avoid transporting firewood. Current management involves sanitation (chipping, burning) of infested material, and chemical treatments may be effective for high value trees.
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