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Posted 9 July 2008. PMN Crop News.

Tree-Killing Fungus Officially Named by Scientists at ISU, Other Institutions

Iowa State University.

Ames, Iowa (June 30, 2008)--An Iowa State University scientist led a team that has officially named the fungus responsible for a devastating disease that’s killing redbay and other trees in the coastal plains of Florida, Georgia and South Carolina.


Tom Harrington, professor of plant pathology at Iowa State, is the lead author of an article about the fungus, which is called Raffaelea lauricola, that was published in the current issue of Mycotaxon, the international journal of fungal taxonomy and nomenclature. The USDA Forest Service Southern Research Station, Asheville, N.C., also made an announcement today about the published research.

“Until now, the fungus was known as the 'laurel wilt pathogen’ because of the devastating disease it causes in redbay trees and other laurel species like sassafras and avocado trees in the Southeast,” said Harrington. “Now arborists, foresters, researchers and regulatory officials have a formal, scientific name and description of the fungus, as well as a detailed explanation of how the pathogen compares to similar fungi.”

Extensive deaths of redbay, an attractive evergreen tree common along the coasts of the southeastern United States, have been observed since 2003. The fungus also has been associated with the deaths of other trees in the laurel family.

Harrington's co-authors on the research are Stephen Fraedrich, a USDA plant pathologist in Athens, Ga., and D.N. Aghayeva, a researcher with the Azerbaijan National Academy of Sciences.

According to Harrington and his colleagues, Raffaelea lauricola is one of many species of fungi carried by ambrosia beetles, a group of highly specialized wood-boring insects that feed on symbiotic fungi, which they carry from tree to tree in specialized sacs. The beetles feed on their own special ambrosia fungi, much as the Greek gods were believed to exist on their "ambrosia."

R. lauricola is the principle ambrosia fungus of an invasive species from Asia, the redbay ambrosia beetle. R. lauricola is the only known tree pathogen among the ambrosia fungi and differs from other Raffaelea species in its DNA sequence and spore sizes. The fungus also grows faster than similar fungi.

Ambrosia beetles introduce the fungus into redbay or other laurel tree species by burrowing into the trees and laying eggs. The fungus serves as a food source for beetle larvae. The pathogen moves through a tree’s vessels causing a vascular wilt disease similar to Dutch elm disease.

Is there any Iowa connection to the pathogen?

"The pathogen is not known to attack any trees native to Iowa, except for sassafras, which is found in the extreme southeastern corner of the state," Harrington said. "Raffaelea lauricola will be of greater impact as it hits the tropical and sub-tropical Americas, where the laurel family is among the most important component of many forests. Avocado also is affected, and the fungus is moving into the avocado growing areas of Florida."

The USDA Forest Service Southern Research Station has more information online about the fungus and the threat it poses to the laurel family at

Tom Harrington
Iowa State University