Laurel wilt is a deadly vascular wilt disease of red bay (Persea borbonia) and other trees in the Laurel family, caused by a fungus (Raffaelea lauricola).

The fungus is carried by a recently-introduced ambrosia beetle (Xyleborus glabratus) that is native to Asia (India, Japan, and Taiwan). The ambrosia beetle was first discovered near Savannah, Georgia in 2002. As the ambrosia beetle bores into the sapwood of stems and branches, the pathogen is transmitted and moves systemically where it plugs up the water conducting cells and causes it to wilt.

Laurel wilt has caused widespread mortality of red bay trees in parks, forests, and residential landscapes on the coastal plains of South Carolina, Georgia, and Florida.

Susceptible Hosts

• Redbay (Persea borbonia), sassafras (Sassafras albidum), pondberry (Lindera melissifolia), pondspice (Litsea aestivalis), avocado (Persea americana), camphor tree (Cinnamomum camphora)

Pest

• The laurel wilt fungus, Raffaelea lauricola, vectored by the redbay ambrosia beetle (Xyleborus glabratus)

Symptoms

• Drooping, wilted leaves with a reddish to purplish discoloration occur on branches and in redbay progress throughout the entire canopy.

• Leaves eventually turn brown and may stay on the tree for up to a year or more.

• A dark, blackish discoloration can be seen in the sapwood when removing the bark from wilted trees or by cutting cross sections of the stem.

• Wilt symptoms on camphor tree may not progress through the entire crown.

Signs

• The redbay ambrosia beetle is extremely small, spends most of its life cycle inside the host tree, and is rarely seen in the field. An adult female is about 1/12 inch (2 mm) long slender, cylindrical, smooth and shiny with a sharp downward slope at the rear. The rear also has a slightly pointed end.

• String-like tubes or piles of fine sawdust may be seen on the bark of trees that have wilted. These are produced by potentially multiple species of ambrosia beetles (including the redbay ambrosia beetle) or other secondary wood borers.

Biology

• Redbay ambrosia beetles are believed to initiate attacks on healthy redbays. Adult flight activity is highest in summer or fall, but the beetle may fly at any time of year in Florida.

• Beetles carry spores of the laurel wilt fungus in their mouthparts.Initial attacks are difficult to detect and may not result in successful colonization of the tree by the beetle. However, these initial attacks can inoculate the tree.

• After becoming infected with the laurel wilt fungus, redbays wilt in a matter of weeks to a few months. The dying tree is then colonized by numerous redbay ambrosia beetles (as well as other ambrosia beetle species) that create galleries in the wood, in which they reproduce and cultivate their associated fungi for food. New female redbay ambrosia beetles emerge from infested trees and fly in search of new hosts, whereas males are flightless.

Distinguishing from Look-alikes:

• The black twig borer (Xylosandrus compactus) results in terminal and small-diameter shoot dieback (or “branch flagging”). However, black twig borer damage is usually spotty, not fatal to large trees, and does not result large contiguous sections of the crown wilting.

Limited trial data suggests that preventive treatments with Alamo injected with 20 ml of Alamo in up to 300 ml of water per inch of DBH will protect trees for at least 18 months.

The residual length of control is unknown, RTSA is currently recommending re-treatment every 18-24 months. It is not known if treatments on trees that are showing early stages of symptoms will be effective

USDA Forest Service

Florida Division of Forestry

Georgia Forestry Commission

The Nature Conservancy

Arboriculture and Urban Forestry Mayfield III, A.E., Barnard, E.L., Smith, J.A., Bernick, S.C., Eickwort, J.M., Dreaden, T.J. 2008. Effect of Propiconazole on Laurel Wilt Disease Development in Redbay Trees and on the Pathogen In Vitro. Arboriculture & Urban Forestry. 34;317-323.