Laurel wilt is also known as laurel wilt disease, it is a vascular disease caused by the Raffaelea lauricola fungus. The fungus is transmitted by the redbay ambrosia beetle. Members of the laurel family died from the disease, with the avocado the most commercially valuable plant affected.
Dark streaking and wilted stems and leaves are symptoms of laurel wilt. There are two ways in which it spreads: one via the beetle’s natural reproduction and migration. The second is through the sale and transport of beetle-infested wood used as firewood and for outdoor grilling.
In Florida, laurel wilt is found as far south as Miami-Dade County, and as far west as Bay County. It can also be found in South Carolina, North Carolina, Mississippi, Alabama, and Georgia. At Savannah, Georgia’s Port Wentworth three adult specimens were trapped at the port in 2002. It is believed they entered the country in solid wood packing material with cargo. In early 2003 Redbay trees began dying in Georgia and South Carolina near Savannah.
Redbay trees that are abundant in the maritime forest of Georgia, South Carolina and Florida have been the most affected by the wilt. A less common tree, the Sassafras in the coastal plains of the Southeast has also been affected but to a lesser extent than the Redbay. Dead and dying pondspice and pondberry have also been isolated with the wilt fungus. However, the redbay ambrosia beetle has not been found in either of these species. While the pondberry is a federally endangered species, the pondspice is regarded as a threatened or endangered species in some southeastern states.
Florida’s avocado crop earns about $65 million wholesale each year and is the second largest fruit crop in Florida after citrus. Laurel wilt and laurel wilt fungus were first seen in 2007 in Jacksonville, Florida. After field and laboratory observations, it was confirmed that the redbay ambrosia beetle had infested avocado trees in the area.
In Miami-Dade County, laurel wilt was detected in 2010 near areas of commercial avocado groves. Since then, avocado groves are being closely monitored for the presence of the redbay ambrosia beetle and signs of the laurel wilt disease.
In order to prevent laurel disease on commercial avocado trees, a Section 18 Emergency Exemption was granted from the EPA in 2011 allowing the use of Tilt which is a formulation of propiconazole. Efficacy and cost-effectiveness of this treatment in commercial grove remain in question.
In February 2011, laurel wilt disease was discovered in swamp bays and by late 2013 dead swamp bay were observed throughout the southern Everglades. Where redbay ambrosia beetles have been found, populations of the redbay and swamp bay have experienced almost a 100% mortality rate of mature trees. This happens within a few years after the first appearance of laurel wilt symptoms.
One of the major components of the tree islands in the Everglades is the swamp bay, a small tree or shrub. It is found in swamp forests, hammocks, and pinelands through the region. Fruits from the swamp bay are consumed by bears, deer, and many songbirds. The foliage is the larval food plant for the swallowtail butterfly.
Further research is needed, but some redbay trees may be resistant to the disease. It is hoped that future research will find a tolerant variety that can be developed.