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Forest Health Protection
Region 8
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Room 816 N
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Laurel Wilt

Plant Susceptibility

 

At this time only plant species in the family Lauraceae indigenous to the southeastern USA are known to be affected by laurel wilt. Redbay, a tree particularly abundant in maritime forests of Georgia, South Carolina and Florida, has been the primary species affected by the wilt. Sassafras, a less common tree in the coastal plains of the Southeast but with a more extensive range than redbay, has also been affected by the disease but to a lesser extent than redbay. The wilt fungus has also been isolated from dead and dying pondspice (Litsea aestivalis) and pondberry (Lindera melissaefolia), however the redbay ambrosia beetle has not been found in either of these species. Pondberry is a federally endangered species while pondspice is regarded as a threatened or endangered species in some southeastern states.

 

Figure 1

Figure 1. Redbay trees are very susceptible to laurel wilt. The wilt is currently occurring in forests of the coastal plains in South Carolina, Georgia and Florida, and is continuing to spread.

 

 

Laboratory inoculation studies have confirmed that redbay and sassafras as well as spicebush (Lindera benzoin) are susceptible to the vascular wilt caused by the Raffaelea lauricola (Figure 2). Additional studies have found that avocado is also susceptible but some cultivars or age classes may be more resistant than redbay and sassafras. In inoculation studies, some avocado seedlings typically wilt and die rapidly, but others remain healthy or only exhibit symptoms such as shoot dieback or foliage discoloration and do not die. As the redbay ambrosia beetle and laurel wilt spread southward in Florida (Distribution Map), mostly in redbay, avocado plants in urban and rural landscapes also have been observed dying and confirmed to be infected with the disease. Some varieties of avocado appear to be more susceptible than others. The serious threat to the avocado industry in south Florida and elsewhere has aroused great concern and a significant research effort is underway to help manage this disease as it moves into the commercial avocado growing area (http://www.fl-dpi.com/enpp/pathology/laurel_wilt_disease.html).

 

 
Figure 2, A
Figure 2, B
 
Figure 2, C
Figure 2, D

Figure 2. Uninoculated "control" plants and plants inoculated with the laurel wilt fungus (Raffaelea lauricola) for: A. redbay (Persea borbonia); B. avocado (Persea americana); C. California bay (Umbellularia californica); and D. sassafras (Sassafras albidum).

 

California bay (Umbellularia californica), a species indigenous to the west coast of the United States, is also susceptible to disease caused by the laurel wilt fungus. In controlled inoculation studies California bay seedlings exhibited shoot and branch dieback. Studies have also been carried out on red maple, tulip poplar and red oak, and these species were not susceptible to the wilt.

 

Numerous species in the Lauraceae occur in the Americas, particularly in the tropical forests of Central and South America where there is great diversification and the species of this family are major components of the forests. Testing is continuing to evaluate the susceptibility of other species in the Lauraceae, as well as other plant families. Additional studies are needed to evaluate the susceptibility of various plant species to the redbay ambrosia beetle since it appears that this beetle is the primary vector of the laurel wilt pathogen.

 

Additional Information

  • Redbay (Persea borbonia) - Taxonomy & Identification - Kim D. Coder, University of Georgia, 1/19/2007 (Handout)

 

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USDA Forest Service - Forest Health Protection, Southern Region
Last Modified: Monday, 16 December 2013 at 14:18:30 CST


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