Laurel Wilt in Florida
In April, scientists with the USDA Forest Service Southern Research Station (SRS), Iowa State University, and the Florida Division of Forestry provided the first description of a fungus responsible for the wilt of redbay trees along the coasts of South Carolina, Georgia, and Florida. The fungus may also be responsible for wilts of other members of the laurel family, including sassafras, spicebush, and avocado.
Extensive mortality of redbay, an attractive evergreen tree common along the coasts of the southeastern United States, has been observed in South Carolina and Georgia since 2003. Though the wilt was at first attributed to drought, the cause was soon found to be a fungal pathogen and the exotic redbay ambrosia beetle, Xyleborus glabratus, a native to Southeast Asia that was first found in the area in 2002. Many ambrosia beetles carry species of fungi as food for their larvae and a previously undescribed fungus in the genus Raffaelea is a fungal symbiont of X. glabratus.
To determine if the fungus was the cause of the wilt, researchers inoculated redbay trees and containerized seedlings with the Raffaelea fungus; the plants died within 5 to 12 weeks. To connect fungus and beetle, they also exposed redbay seedlings to X. glabratus beetles; the ambrosia beetles tunneled into almost all of the plants, causing 70 percent of them to die. The researchers found the fungus in 91 percent of the beetle-attacked plants. The fungus, which is routinely isolated from the heads of X. glabratus ambrosia beetles, is apparently introduced into healthy redbay during beetle attacks on stems and branches.
Redbays are common along the Southeastern coast, and both residents and visitors are disturbed by the massive mortality. The fungus has also been associated with the death of other trees in the laurel family such as sassafras, pondberry and pondspice as well as spicebush and avocado, but not to red maple. The researchers concluded that there is reason to be concerned about the spread of the wilt to other members of the laurel family, which are common components in forests across the United States and other areas of the Americas. Evaluation of avocado indicates that it is also susceptible to laurel wilt, and the wilt has been found recently in avocado trees growing in a residential area of Jacksonville, Florida. (USDA SRS, 4/4/08).
