Laurel Wilt

Raffaelea lauricola & Xyleborus glabratus

Eichhoff

Last updated by: 
Faith Campbell

Laurel wilt - 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. 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 6 states, reaching from eastern North Carolina south along most of the Florida peninsula and west to several locations in Alabama and Mississippi (Mayfield et al. 2013; Riggins et al. 2010). See map, accurate as of August 2012.

 

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, logs, and chipped host material (Mayfield et al. 2009).

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 only known vector of the pathogen (Mayfield et al. 2009). 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).

 

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).   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).

 

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 in the Atlantic Coastal Plain; the pathogen and vector have not yet spread into the more upland and northern portions of the sassafras range (Mayfield et al. 2013).  Studies of the beetles’ willingness to attack sassafras have produced conflicting reports; Mayfield and colleagues (2013) found sassafras to be as attractive to the beetles as both swampbay and silkbay (Persea humilis).  They suggest two possible explanations for the differing results: either differences in treatment of the bolts used in the studies caused variations in moisture levels or other attributes in the wood; or individual trees belonging to the same species might vary in their attractiveness to the beetles (Mayfield et al. 2013).

 

Can the laurel wilt disease spread throughout the wide range occupied by sassafras?  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. 

 

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).

 

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 avocado industry has prepared a recovery plan.

 

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 http://terrain.org/articles/22/cerulean.htm.

 

 

Table 1.  Summary of Lauraceae in the US*

Plant Name

US Status

Genus

Species

Common

Native

Introduced

Cassytha

filiformis

Love-vine, Woe-vine, Devil’s gut

 

Cinnamomum

camphora

Camphor tree

 

(Tropical  Southeast Asia)

Cinnamomum

verum

Ceylon cinnamon, Cinnamon

 

√ (Sri Lanka, India & Myanmar)

Cryptocarya

mannii

Holio

 

Larus

nobilis

Bay, Grecian laurel, Laurel, Sweetbay

 

(Mediterranean)

Licaria

trainers

Gulf triandra

 

Lindera

benzoin

Feverbush, Spicebush, Wild allspice

 

Lindera

melissifolia

 

 

Lindera

subcoriacea

Bog spicebush

 

Litsea

aestivalis

Pondspice

 

Nectandra

coriacea

Lancewood

 

Nectandra

hihua

Shinglewood

 

Nectandra

krugii

Krug's sweetwood

 

Nectandra

membranacea

Sweetwood

 

Nectandra

patens

Capberry

 

Nectandra

turbacensis

Laurel amarillo

 

Ocotea

floribunda

Laurel espada

 

Ocotea

foeniculacea

Black sweetwood

 

Ocotea

leucoxylon

Loblolly sweetwood

 

Ocotea

moschata

Nemoca

 

Ocotea

nemodaphne

Laurel sassafras

 

Ocotea

portoricensis

Laurel de paloma

 

Ocotea

spathulata

Nemoca cimarrona

 

Ocotea

wrightii

Wright's laurel canelon

 

Persea

americana

Avocado

 

(South America

Persea

borbonia

Redbay

 

Persea

palustris

Swamp redbay

 

Persea

humilis

Silk bay

 

Sassafras

albidum

Sassafras

 

Umbellularia

californica

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

 

Umbellularia

californica var. californica

 

 

Umbellularia

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

 

-------------------------

Sources

 

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:http://www.fs.fed.us/r8/foresthealth/laurelwilt/resources/pubs/georgia_laurel_wilt_report_2006-08.pdf

 

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 http://www.ars.usda.gov/research/npdrs.

 

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

 

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 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.

 

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.

 

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