Laurel Wilt Disease Associated With Redbay Ambrosia Beetle
Laurel wilt, a new disease of redbay (Persea borbonia) and other plant species in the family Lauraceae, is causing widespread mortality in the coastal regions of South Carolina, Georgia, and Florida. The disease is caused by a fungus (Raffaelea species) that is introduced into trees by an exotic insect, the redbay ambrosia beetle (Xyleborus glabratus). The redbay ambrosia beetle is native to Asia and is the 12th new species of ambrosia beetle introduced into the U.S. since 1990.
Redbay trees grow in the Coastal Plain region from eastern Texas to Virginia and are ecologically and culturally important, although of minor commercial timber value. Redbay trees provide fruit for song birds, turkey, and quail, deer and black bear browse on the foliage and fruits. Additionally, the larvae of the Palamedes swallowtail butterfly require redbay leaves for development.
The redbay ambrosia beetle was discovered in Savannah's Port Wentworth area in spring 2002; however, it is likely to have been established in the area prior to 2002 when the three adult specimens were trapped at the port. The beetle likely entered the country in solid wood packing material with cargo that was imported at Port Wentworth. Redbay trees began dying in Georgia and South Carolina near the Savannah area in 2003. By early 2005, officials with the Georgia Forestry Commission (GFC), South Carolina Forestry Commission (SCFC), and US Forest Service began to suspect the newly discovered ambrosia beetle was associated with this mortality. Subsequent research since 2005 has found that the mortality is caused by a pathogenic fungus that is carried by the redbay ambrosia beetle. The fungus is believed to be transmitted to healthy redbay trees when they are attacked by the beetle, resulting in a wilt disease. The disease has also been discovered in individual plants of the federally endangered pondberry (Lindera melissifolia), the threatened pondspice (Litsea aestivalis), sassafras (Sassafras albidum) and avocado (Persea americana).
Many native ambrosia beetles (40 plus species) occur in the United States and primarily target stressed or dying trees. In general, ambrosia beetles carry specific fungi that are introduced into the trees as they tunnel into the wood, and are fed upon by the developing insects. In the case of the redbay ambrosia beetle, one of the associated fungi also acts a pathogen as it spreads through the tree's vascular system, causing the trees to wilt and die. This associated fungus is in the same class of fungi as those that cause Dutch elm disease and blue stain in pines.
All of Georgia's coastal counties now have confirmed laurel wilt and the disease is moving northward in South Carolina, southward in Florida, and inland at an alarming rate. In 2004, South Carolina, Georgia, and Florida reported three counties with damage; now the disease has spread to 32 total counties. Officials estimate that natural spread is about 20 miles per year, but movement of infested firewood, wood chips and logs may be a major factor in spreading the disease into new locations not contiguous with main area of infestation. Landowners, loggers, and others are asked to leave dead redbay trees in the woods and not salvage them for logs, chips or firewood. It is likely that long distance spread via wood movement has occurred already, and the public is asked to cooperate with this voluntary request by state and federal agencies.
There are no proven management strategies for preventing the development of laurel wilt disease. Early sanitation of newly infested trees and limiting movement of infested wood may help slow the spread. Field trials evaluating the effectiveness of certain pesticides are being conducted in Florida and Georgia. Formal ground surveys are being conducted by the SCFC and the GFC to develop baseline infestation information. Research is ongoing with the US Forest Service - Southern Research Station (Athens, GA and Pineville, LA), Louisiana State University, Iowa State University, University of Florida, and Florida DACS-DOF. A regional meeting highlighting the research and current information available on this problem was held in January at Jekyll Island, Georgia and was sponsored by the GFC, SCFC, Florida Department of Agriculture and Consumer Services Division of Forestry (DACS-DOF), and US Forest Service. Substantial information about this problem is available at: http://www.fs.fed.us/r8/foresthealth/laurelwilt.shtml.
- James Johnson - Georgia Forestry Commission
- Laurie Reid - South Carolina Forestry Commission
- Bud Mayfield - Florida Department of Agriculture & Consumer Services - Division of Forestry
- Don Duerr - US Forest Service - Forest Health Protection
- Stephen Fraedrich - US Forest Service - Southern Research Station
Brief History in Georgia
Summer 2002 - A GFC employee, funded under the U.S. Department of Agriculture Animal and Plant Health Inspection Service's Exotic Bark Beetle Survey, caught an unknown ambrosia beetle near Port Wentworth. Dr. Bob Rabaglia, an entolmologist with the USDA Forest Service, identified the specimen as Xyleborus glabratus and completed a threat assessment of the species (mostly unknown, but listed as a moderate risk).
Summer 2004 - An unexplained redbay mortality was reported in the Savannah/Chatham County area. Initial diagnosis (GFC) attributed this mortality to a combination of drought stress and the Asian ambrosia beetle (Xylosandrus crassiusculus) due to typical frass tubes being present on many samples. Insects were later recovered from samples and sent to Dr. Bob Rabaglia who confirmed the presence of Xyleborus glabratus.
July 2005 - The Georgia Redbay Task Force was formed in July 2005 to bring industry, government and academia together to share information and further study the problem. Task Force participants include: Georgia Forestry Commission, US Forest Service - Southern Research Station & Forest Health Protection, Animal & Plant Health Inspection Service, University of Georgia, Georgia Forestry Association, Forest Industry, US Fish &Wildlife Service, Georgia Department of Natural Resources, The Nature Conservancy, National Park Service, and US Department of Defense at Fort Stewart, Georgia.
A suppression effort on Jekyll Island, cutting and removing infested redbay, took place in mid-December 2006 and limited insecticide treatments on significant trees are being tested for disease prevention.