Laurel Wilt

Raffaelea lauricola & Xyleborus glabratus


Last updated by: 
Faith Campbell

Laurel wilt - redbay ambrosia beetle Xyleborus glabratus and associated fungus Raffaelea lauricola


NOTE: the ambrosia beetle and fungus complex attacking avocadoes and other trees in California are completely unrelated organisms to Laurel wilt, despite both being beetle-fungi complexes that affect avocado trees. Click here to read about the polyphagous shot hole borer and Fusarium fungus.


Beginning in 2003, scientists began receiving reports of dying redbay trees (Persea borbonia ) in coastal areas of Georgia and South Carolina (J. Johnson, Georgia Forestry Commission, pers. comm. 4 April 2005), then in northeast Florida (J. Foltz, University of Florida, pers. comm. November 2005). The cause was determined to be a previously unknown fungus, Raffaelea lauricola) transported (vectored) by a recently introduced ambrosia beetle from Asia, Xyleborus glabratus (Fraedrich et al. 2008). The beetle had first been detected in the United States in 2002 near Savannah, Georgia (Rabaglia et al. 2006).

The disease has since spread rapidly.  It now is found in 8 states, reaching from eastern North Carolina south along most of the Florida peninsula; and several locations in Alabama and Mississippi (Mayfield et al. 2013; Riggins et al. 2010); with isolated outbreaks in Louisiana and Texas. See map, above. 

 The beetle can apparently fly several kilometers; it might also be carried on wind currents (Mayfield et al. 2009). There is also evidence that it can be transported by human movement of infested wood. Thus, in addition to the initial detection of the beetle near a port which receives significant amounts of wood packaging, several isolated outbreaks can be traced to movement of wood - e.g., those near a hardwood mulch plant and a state park in Georgia (Cameron et al. 2008); and near the shop of a woodturner who collected redbay logs from an infested area in Florida (Mayfield et al. 2009). The suspected pathways of long distance spread include infested solid wood packing material, firewood, and logs (Mayfield et al. 2009).  Wood chips are no longer considered likely to spread either the beetle or the fungus (J. Smith, 2015).

Because the beetle can reproduce without mating, a population in a new, isolated location can potentially be started by only one female – as long as it finds suitable host material (Mayfield et al. 2009).

After a redbay tree has died, it is typically attacked by additional redbay ambrosia beetles. Later, female beetles emerging from the dead redbay tree disperse in search of new hosts. Dead redbay trees can serve as host material for the beetle for many weeks after initial colonization. Many coastal forests have up to hundreds of redbay trees per acre, allowing redbay ambrosia beetle populations to build rapidly (Mayfield et al. 2009).

The redbay ambrosia beetle is native to Asia where its reported hosts include several species in the families Lauraceae, Dipterocarpaceae, Fagaceae (oak family), and Fabaceae (bean family) (Rabaglia et al. 2006). No laurel wilt disease is reported in these or other plant species in the beetle’s native range.

Redbay ambrosia beetle is the principal vector of the pathogen (Mayfield et al. 2009).  However, it is now suspected that other ambrosia beetle species can transfer the pathogen.  This appears to be occurring especially in avocado, which is rarely attacked by the redbay ambrosia beetle (T. Dreaden and D. Carrillo. 2015). Attack by even a single female beetle is sufficient to inoculate the tree with sufficient numbers of spores of Raffaelea lauricola to initiate disease (Mayfield et al. 2009). The pathogen moves throughout the tree through the sapwood, presumably causing a restriction in the flow of water and wilting of the leaves. In redbay, the entire crown eventually wilts and turns brown over a period that may take from a few weeks to 2-3 months (Mayfield et al. 2009).

More than 90% of redbays with stems greater than 1 inch diameter have died within 2 years in some stands (Fraedrich et al. 2008). Smaller diameter redbay seedlings and sprouts appear to be much less frequently affected by the disease in the field (Fraedrich et al. 2008). Scientists expect continued dramatic reductions in redbay populations, although survival of redbay regeneration in the aftermath of laurel wilt epidemics suggests that redbay will not go extinct (Mayfield et al. 2009).  A team of USDA Forest Service scientists has predicted that redbay will lose 90% of its basal area before 2030 (USDA FS 2014).

Redbay is important to wildlife. The fruit is eaten by wild turkey, bobwhite quail and several species of song birds. Deer also consume the fruits and leaves (Brendemuehl, 1990). An additional ecological concern is the dependence of the Palamedes swallowtail butterfly (Papilio palamedes) on redbay and swamp bay (Persea palustris); the butterfly’s larvae feed on these trees – both of which have been killed in large numbers (Mayfield et al. 2013).  The adult Palamedes swallowtail butterfly is the primary pollinator of yellow-fringed orchid (J. Riggins 2015).  A second butterfly, the spicebush swallowtail (Papilio troilus), is also dependent on species in the family Lauraceae and might be harmed if the pathogen proves to damage additional woody plants in that family (J. Foltz, University of Florida, pers. comm. November 2005).

While redbay is found primarily in the live oak maritime forests, swamp bays grow in a wide variety of habitats in the everglades ecosystem, especially on “tree islands” scattered through the sawgrass swamp. Tree islands comprise only about 10% of the everglades landcover, but contribute greatly to biological diversity and ecosystem process, including as wet season refugia for mammals. The result of widespread swamp bay mortality is expected to be reduced food availability for dependent mammals and insects and – where the canopy is opened, invasion by non-native plants (T. Pernas 2015).  

Laurel wilt has spread quickly across Everglades National Park and Big Cypress National Preserve; the extent of infected trees covered 372,000 ha in just four years from the first detection in 2011.  The disease has reached the edge of vulnerable trees on the Southwest side, but can still spread to the North.  Officials believe the rapid spread was helped by the wind, which blows predominantly East to West from February through October.  The disease has not become virulent in the Loxahatchee National Wildlife Refuge to the Northeast; the reason is unclear but might be related to the fact that this area does not have a prolonged dry spell (L. Rodgers 2015). 

Other native forest species that host the disease include sassafras (Sassafras albidum) and two rare species – pondspice (Litsea aestivalis) (listed as endangered in South Carolina but found through much of the southeastern coastal plain) and the federally listed pondberry (Lindera melissifolia). Sassafras is being killed at various sites in the Atlantic Coastal Plain (Mayfield et al. 2013) and is supporting the infestation in Alabama and Louisiana.  Disease symptoms on sassafras are much more subtle so outbreaks are probably escaping detection (C. Bates 2015).

Sassafras occupies a large range reaching into Michigan and southern New England. Can the laurel wilt disease spread throughout this range?  Scientists don’t know.  A second group of scientists is looking at how far north the redbay ambrosia beetle might spread.   Formby et al. (2013) found that after artificial cold hardening, the redbay ambrosia beetle could withstand a supercooling point sufficiently low to allow it to survive - theoretically - throughout much of North America  [see Formby map]. Formby notes that supercooling data alone cannot predict an insect’s invasion potential, so research continues.   Another puzzle: what proportion of beetles remaining alive after exposure to cold is “safe” – since a lone beetle can establish infection in a vulnerable host?  Scientists don’t know (J. Riggins 2015).

Northern spicebush (Lindera benzoin (L.) Blume) – another shrub in the Lauraceae family, which has a huge range in the eastern deciduous forest – has been determined not to attract the beetle so it is unlikely to sustain disease (Mayfield et al. 2013) – although the shrub appears to be vulnerable to the pathogen itself (Mayfield et al. 2009).

Redbay and swamp bay provide key ingredients in 90% of traditional medicines used by the Seminole & Miccosukee tribes of Florida.  The tribes are supporting scientific efforts to find, propagate, and restore swamp bay trees resistant to the disease (J. Smith and Lanette Sobel 2015).

There is concern that an important tree or shrub of the far West – California laurel (Umbellularia californica) – might prove vulnerable.  This evergreen grows across a variety of sites in the Pacific coastal regions of Southwest Oregon, western California, and the foothills of the Cascade Range and Sierra Nevada mountains.  The fruit is fed on by squirrels, jays and other animals.

In studies undertaken by Mayfield et al. (2013), the redbay ambrosia beetle was as able to enter and reproduce in California bay laurel as in sassafras and swampbay.   The authors conclude that California bay laurel would probably perpetuate the laurel wilt disease cycle if the pathogen is sufficiently virulent to kill mature California bay laurel trees.  This latter issue is not yet resolved; earlier lab studies indicated that the pathogen does cause sapwood discoloration and some branch wilt and dieback in bay laurel seedlings (Fraedrich, 2008).

 Like redbay, California bay laurel has attractive wood used for cabinetry, furniture, veneer and other specialty wood products (Mayfield et al. 2013).  This means that there is a risk that the disease could be transported by the woodworker community.  A complicating factor is that California bay laurel is a reproductive host for the sudden oak death pathogen, Phytophthora ramorum [link to Gallery writeup].   Bay laurels growing in SOD-infested counties are subject to quarantine restrictions.

 The greatest economic impact from laurel wilt disease could be to Florida avocados (Persea americana Mill. ); yard trees and experimentally planted avocados in coastal Florida have been killed (Mayfield et al. 2009).  The disease was detected in commercial orchards in 2012 (D. Carrillo 2015) .  The avocado industry has prepared a recovery plan.  The plan calls for early detection and rapid removal of diseased trees to avoid creating “beetle factories”.  As of June 2015, 9,000 trees had been removed – about 1% of total numbers.  This removal is expensive because of the size of the trees and their interlocking roots – so some landowners have abandoned their orchards.  Since the disease is not considered a quarantine pest, there are no legal requirements that growers follow the protocol (D. Carrillo 2015).

Management of the disease in avocado groves is complicated by the variety of ways in which the disease can spread – both by several of the ambrosia beetle species common in the area and by neighboring trees’ fusing their root systems.  The avocado industry is funding intensive insect trapping and research into control methods (D. Carrillo 2015).

 It appears to be too late to stop the spread of laurel wilt throughout the range of redbay and perhaps into other plant communities as well. Research is needed on tools to manage the beetle and the disease.

 California avocado growers are dealing with a separate insect/pathogen disease complex.  The polyphagous shot hole borer is a previously undescribed beetle in the Euwallacea genus that vectors a Fusarium fungus – also previously undescribed.  The disease complex is already established in the Los Angeles area.


A compelling article about laurel wilt, as it is killing red bay (Persea borbonia), was written by Susan Cerulean, and has been posted on line at



Table 1.  Summary of Lauraceae in the US*

Plant Name

US Status








Love-vine, Woe-vine, Devil’s gut




Camphor tree


(Tropical  Southeast Asia)



Ceylon cinnamon, Cinnamon


√ (Sri Lanka, India & Myanmar)







Bay, Grecian laurel, Laurel, Sweetbay





Gulf triandra




Feverbush, Spicebush, Wild allspice








Bog spicebush
















Krug's sweetwood












Laurel amarillo




Laurel espada




Black sweetwood




Loblolly sweetwood








Laurel sassafras




Laurel de paloma




Nemoca cimarrona




Wright's laurel canelon






(South America







Swamp redbay




Silk bay








Calif. bay, Calif. laurel, Oregon-myrtle, Myrtle-wood, Pepperwood



californica var. californica




californica var. fresnensis





* Source for the table is James Johnson, Georgia Forestry Commission





Lauraceae in Puerto Rico (D.J. Lodge, U.S. Forest Service, pers. comm. June 2013)

Aniba bracteata

Beilschmiedia pendula

Cinnamomum burmannii

Cinnamomum zylanicum

Licaria brittoniana

Licaria salicifolia

Licaria triandra

Nectandra patens

Nectandra coriacea

Nectandra krugii

Nectandra membranacea

Nectandra sintenisii

Ocotea cuneata

Ocotea floribunda

Ocotea foeniculacea

Ocotea leucoxylon

Ocotea moschata

Ocotea portoricensis

Octotea wrightii

Persea americana

Persea krugii

Persea urbaniana

Phoebe elongata


For more information on this pest/fungal complex, please visit:





Bates, Chip. 2015.  Presentation  at the “Conference on Laurel Wilt Disease & Natural Ecosystems”, Coral Springs, Florida; June 2015.

Brendemuehl, R. H. 1990. Persea borbonia (L.) Spreng. Redbay. Pg. 503-506 in Silvics of North America. Volume 2. Hardwoods. USDA Forest Service. Agriculture Handbook 654.Washington, DC.

Cameron, R.S., Bates, C., and Johnson, J. 2008. Distribution and Spread of Laurel Wilt Disease in Georgia: 2006-08 Survey and Field Observations. Georgia Forestry Commission report. September 2008. 28 p. Available online at:

Carrillo, Daniel. 2015.  Presentation at Conference on Laurel Wilt Disease  & Natural Ecosystems, Coral Springs, Florida; June 2015.

Dreaden, Tyler and Daniel Carrillo. 2015. Presentation at the “Conference on Laurel Wilt Disease & Natural Ecosystems”, Coral Springs, Florida; June 2015.

Formby, J.P., N. Krishnan, and J.J. Riggins. 2013.  Supercooling in the Redbay Ambrosia Beetle (Xyleborus glabratus)-  Preliminary implications of invasion potential in North America; poster presented at the 24th USDA Interagency Research Forum on Invasive Species, Annapolis, MD January 8-11, 2013

Fraedrich, S.W., Harrington, T.C., Rabaglia, R.J., Ulyshen, M.D., Mayfield A.E. III, Hanula, J.L, Eickwort, J.M. and Miller, D.R. 2008. A fungal symbiont of the redbay ambrosia beetle causes a lethal wilt in redbay and other Lauraceae in the southeastern USA. Plant Disease 92:215-224.

Mayfield, A., Barnard, E., Bates, C., Boone, A., Bulluck, B., Cameron, S., Campbell, F., Duerr, D., Fraedrich, S., Hanula, J., Harrington, T., Johnson, J., Peña, J., Rabaglia, R., Smith, J., Vankus, V. 2009. Recovery plan for laurel wilt on redbay and other forest species caused by Raffaelea lauricola, vector Xyleborus glabratus. National Plant Disease Recovery System, a cooperative project of

The American Phytopathological Society and The United States Department of Agriculture, posted at

Mayfield, A.E., M. MacKenzie, P.G. Cannon, S.W. Oak, S. Horn,  J. Hwang, and P.E. Kendra. 2013. Suitability of California bay laurel and other species as hosts for the non-native redbay ambrosia beetle and granulate ambrosia beetle. Agricultural and Forest Entomology (2013), DOI: 10.1111/afe.12009

Pernas, Tony. 2015.  Presentation at the “Conference on Laurel Wilt Disease & Natural Ecosystems”, Coral Springs, Florida; June 2015.

Rabaglia, R.J., Dole, S.A., and Cognato, A.I. 2006. Review of American Xyleborina (Coleoptera: Curculionidae: Scolytinae) occurring north of Mexico, with an illustrated key. Annals of the Entomological Society of America 99: 1034-1056.

Riggins, John. 2015.  Presentation  at Conference on Laurel Wilt Disease & Natural Ecosystems, Coral Springs, Florida; June 2015.

Riggins J. J, Hughes, M., Smith, J.A., Mayfield, A. E. III, Layton, B., Balbalian, C. and Campbell, R. 2010. First occurrence of laurel wilt disease on redbay trees in Mississippi. Plant Disease 94: 634.

Rodgers, LeRoy. 2015.  Presentation at the “Conference on Laurel Wilt Disease & Natural Ecosystems”, Coral Springs, Florida; June 2015.

Smith, J.A., Dreaden, T.J., Mayfield, A.E. III, Boone, A., Fraedrich, S.W., and Bates, C. 2009. First report of laurel wilt disease caused by Raffaelea lauricola on sassafras in Florida and South Carolina. Plant Disease 93: 1079.

Smith, Jason. 2015.  Presentation  at the conference “Conference on Laurel Wilt Disease & Natural Ecosystems”,  Coral Springs, Florida; June 2015.

Sobel, Lanette. 2015.  Presentation  at the conference “Conference on Laurel Wilt Disease & Natural Ecosystems”,  Coral Springs, Florida; June 2015.

United States Department of Agriculture Forest Service. Forest Health Technology Enterprise Team. 2014.  2013-2027 National Insect and Disease Forest Risk Assessment.  FHTET-14-01

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