What to Know About the Laurel Wilt

Sassafras Trees Face a Deadly New Foe

Sassafras trees in Nashville and Middle Tennessee are under threat from a fungal disease that skipped across hundreds of miles and reached our region sooner than expected.

The deadly fungus, known as Laurel wilt, could wipe out the lovely native Sassafras tree (Sassafras albidum) and other trees of the Laurel family (Lauraceae) in our yards, parks and woodlands, just as it has devastated other tree species on the southern Atlantic coast where it originated. The USDA estimates that hundreds of millions of coastal Redbay trees have already been killed by Laurel wilt; sadly, millions more trees in the Laurel family are expected to follow.

Sassafras trees killed by Laurel wilt in the Whites Creek area.

The disease was first detected in Davidson County in 2020, and more dead and dying Sassafras trees with Laurel wilt have recently been identified in Whites Creek, in the northwest part of the county.

The Culprit

Laurel wilt began its deadly march through the southeastern U.S. in 2002, when a non-native insect, the Redbay ambrosia beetle, was first found in a trap near Savannah, Georgia. It likely hitched a ride on wood packing materials that arrived at a nearby port. Although other ambrosia beetles are beneficial bugs that speed up the decay of dead trees, this Asian beetle attacks healthy trees and carries a lethal pathogen, Raffaelea lauricola, the fungus that causes Laurel wilt. The disease affects water conduction, causing leaves of infected trees to wilt, turn brown and die within weeks. The sapwood of the trees, when cut, is typically stained dark brown.

The Leap to Tennessee

The disease progressed mostly in the coastal areas of South Carolina, Georgia and Florida before making a leap across several hundred miles to Montgomery County, Tennessee in 2019. It’s now present in 14 of Tennessee’s 95 counties.

“It can only be speculation at this point, but it seems the most likely way it reached Middle Tennessee was some accidental transport via the Army between one of the coastal bases (in areas where it had been spreading for years) to Fort Campbell, the first place it was found in our region, well away from any other known instances,” says Michael Davie, NTCC board member and certified master arborist at Bartlett Tree Experts. “I’ve seen it at Fort Campbell, a few scattered locations around Davidson County, and I’ve seen what looks like it in Williamson, Cheatham and Wilson counties.”

Stopping the Spread

No effective treatment for the disease has been found, though genetic research on the pathogen is under way. “An injection system using fungicide [has been developed]; however, it isn’t easily applied, and the applicator must hold a pesticide certified applicators license,” says Diane Warwick, Urban and Community Forestry Program Coordinator with the Tennessee Department of Agriculture. “The treatment only lasts for one year, and if the plant is showing any symptoms it is already too late to stop the progression of the disease.” She believes that only select Sassafras, such as specimen trees in arboretums or historic/landmark trees, would be candidates for this treatment.

If you suspect Laurel wilt is affecting your trees, Michael Davie recommends contacting a qualified arborist or collecting a sample to bring to your county extension office. “Make sure it’s a symptomatic branch, not dead, not alive and normal, but a dying branch, especially with dark staining in the wood,” he says.

Meanwhile, forest scientists say it’s crucial that no firewood or logs in affected areas are transported to other regions. Any affected trees that are cut should be chipped, with the mulch remaining on site (a study has shown that the fungus does not survive in mulched wood chips). You can do your part to slow the progress of this destructive disease by keeping any cut Sassafras trees on your own property and buying firewood only from trusted sources.

The Spicy Sassafras

The loss of the Sassafras tree would be a painful blow to those who appreciate its aroma in Southern woodlands and its storied history. Because of its unique leaf structure, Sassafras is one of the easiest trees to identify — some leaves are plain ovals, some have one big and one smaller lobe (like a mitten), while some leaves have three lobes (like a glove).

A sapling in Warner Park shows the three distinct shapes of Sassafras leaves: oval, mitten (2-lobe) and glove (3-lobe).

The spicy bark of the Sassafras root has long been used as a medicinal tonic, and it was the key ingredient in root beer when commercial production began in the 19th century. Safrole, which gives sassafras root its distinctive flavor, was determined to be a possible carcinogen and banned by the FDA in 1960. As a result, artificial flavor or safrole-free sassafras extracts are now used to make root beer. The dried leaves of Sassafras trees are also used to make file powder, a key ingredient of gumbo.

Unfortunately, the Sassafras tree is not the only tree in imminent danger from this fungal disease. Other members of the Laurel family that are known to be susceptible include:

Swamp bay (Persea palustris)
Silk bay (Persea humilis)
Northern spicebush (Lindera benzoin)
Pondberry (Lindera melissifolia)
Pondspice (Litsea aestivalis)

Plants with "laurel" in their names that are not actually members of the Lauraceae family, like mountain laurel, are not at risk. However nonnative species in the Lauraceae family, including avocado and bay laurel trees, are susceptible. The disease has already killed tens of thousands of avocado trees in Florida and if it reaches California, the leading state in avocado production, the results could be even more devastating.

Check these resources for more information on Laurel wilt:

USDA National Invasive Species Information Center

U.S. Forest Service Southern Region Pest Alert

University of Florida Depart of Entomology and Nematology - Featured Creatures

Don’t Move Firewood - Laurel Wilt

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