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.

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.

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)

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USDA Forest Service - Forest Health Protection, Southern Region
Last Modified: Friday, 17 May 2013 at 12:04:05 EDT