USDA Forest Service
 

Forest Health Protection, Southern Region

 
Forest Service Headquarters
FHP Headquarters
Southern Region
State and Private Forestry
   
  FirstGov Link
   
  Evaluate Our Service
We welcome your comments and suggestions for improvement.

USDA Forest Service
Forest Health Protection
Region 8
1720 Peachtree Road, NW
Room 816 N
Atlanta, GA 30309

Phone: (404) 347-7478
Fax: (404) 347-1880

United States Department of Agriculture Forest Service.

Florida Forest Service USDA-APHIS Georgia Forestry Commission South Carolina Forestry Commission USDA Forest Service

Laurel Wilt

Disease Cycle

Graphical Depiction of the Laurel Wilt Disease in Redbay [PDF 830 KB]

 

The pathogen that is the cause of laurel wilt is a fungal associate of the redbay ambrosia beetle. The fungus resides in specialized pouches (mycangia) within the head of beetles. The fungus is thought to ooze out of the mycangia and enter the water conducting tissues (xylem) of redbay and other susceptible hosts as beetles bore into trees. Spores of the fungus reproduce and spread within the xylem and probably plug the tree’s water conducting tissue, resulting in wilt. Many questions remain about the infection of trees. We do not fully understand if the beetles attack preferentially at specific locations on trees. Field observations indicate that the redbay ambrosia beetles can attack smaller branches in the upper crowns of trees, but we have also found isolated attacks by the beetles on the main stems of apparently healthy trees. Healthy trees are not attacked in mass by the redbay ambrosia beetle, and often, trees that are in the initial stages of wilt have evidence of relatively few beetle attacks.

 

Figure 1, A Figure 1, B

A) Redbay tree beginning to show symptoms of wilt; and, B) sapwood discoloration in stem with isolated entrance holes (at arrows) from the redbay ambrosia beetle. (Hunting Island State Park, SC, March, 2006).

 

At this time, we also do not understand if the initial attacks on healthy trees occur only at certain times of the year or if attacks occur during any season when the beetles are active. Similarly, the time between attacks by the beetle on healthy trees and the development of wilt symptoms in crowns of trees is the subject of much speculation.
As trees die they are increasingly attacked by the redbay ambrosia beetle as well as other beetles. Tunnels excavated into these dead and dying trees become “homes” for the ambrosia beetles and significant numbers of offspring are produced in these trees. The redbay ambrosia beetles that emerge from dead and dying redbay trees carry the laurel wilt fungus, and the beetles can spread the fungus to healthy trees.


Figure 2, A Figure 2, B

A) Redbay tree in the advanced stages of wilt; and B) stem of wilted redbay with multiple beetle attacks. Note the frass-tubes or “toothpicks” that are produced as beetles bore into trees. (Fort George Island, FL, October, 2005).

 

Additional Information

  • An Ophiostoma (anamorph = Raffaelea ) species and Xyleborus glabratus Threaten Redbay and Other Members of the Lauraceae Family in the Southeastern USA - Stephen W. Fraedrich, USDA Forest Service, Thomas C. Harrington, Iowa State University, and Robert J. Rabaglia, USDA Forest Service, 1/19/2007 (Abstract, 13 KB) (Slideshow, 3.3 MB)

 

[ Adobe™ PDFdocuments on this page require the free Adobe Acrobat Reader. See Disclaimers ]

 

< Back

 

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


USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.