Prevention is Key: Lessons from Laurel Wilt

sassafras-tree-laurel-wilt
An infected sassafras tree in Louisiana shows dead branches, a symptom of laurel wilt disease. Photo by Rabiu Olatinwo, USFS.

Since 2002, forests in the southeastern U.S. have struggled against a disease called laurel wilt. In 18 years, laurel wilt has spread to 11 southeastern states and killed hundreds of millions of trees.

A review article by USDA Forest Service scientist Rabiu Olatinwo reflects on the origins and spread of laurel wilt throughout the last several years.

Olatinwo, a research plant pathologist at the SRS, published this research with recently retired plant pathologist Stephen Fraedrich and research entomologist Bud Mayfield in the journal Forests.

Laurel wilt is a disease that causes tree death, mainly affecting redbay, sassafras, and avocado trees. Laurel wilt is caused by two nonnative, invasive species from Asia: the redbay ambrosia beetle (Xyleborus glabratus) and an associated fungus (Raffaelea lauricola).

Olatinwo explains that the fungus (also called the pathogen) and the beetle are a very successful team. “The beetle transports the pathogen to the trees. The pathogen kills the tree in a way that is helpful to the beetle.”

The spread of laurel wilt throughout the southeastern U.S. has been extremely rapid due to a number of factors:

  • High densities of vulnerable trees: coastal forests had hundreds of redbay trees per acre;
  • Favorable climate for the fungus and beetle: the warm, humid climate of the Southeast has allowed the ambrosia beetle to thrive;
  • Accidental spread by humans: the movement of infested firewood from one location to another has allowed laurel wilt to spread across long distances;
  • Delayed understanding of the cause of laurel wilt: Although the first case of laurel wilt occurred in 2002, scientists did not have a conclusive understanding of the disease until 2005.

Laurel wilt has been devastating to southeastern forests, causing substantial losses of redbay trees in Georgia, South Carolina, and Florida. Now, laurel wilt is moving into areas where sassafras is more common and will continue to reduce the number of these trees.

redbay-ambrosia-beetle
A female redbay ambrosia beetle (pictured) carries the fungal pathogen between trees, allowing laurel wilt to spread. Photo by Rabiu Olatinwo, USFS.

Along with these ecological changes, laurel wilt has caused economic and commercial damage.

Of greatest economic importance is the avocado industry in southern Florida, which accounts for 10 percent of avocado production in the U.S. Laurel wilt could mean at least $183 million in economic losses if orchard managers are unable to prevent spread within avocado groves.

Because of the economic and environmental consequences of diseases like laurel wilt, something must be done to protect U.S. forests from invasive pests and plant disease. But what can we do? Olatinwo’s answer is prevention.

Once a nonnative, invasive species finds its way into forest ecosystems, it may be too late to save the trees. Preventative action is essential. Laurel wilt is a prime example: even though 20 years have passed since the beginning of the epidemic, there are still few ways to contain the spread.

Olatinwo explains that after a disease is already established, it can be difficult to coordinate all the measures needed to contain it. With prevention, on the other hand, “you can control where it is and manage it properly.”

While we can’t go back in time to prevent laurel wilt, we can heed this lesson to prevent future diseases that threaten U.S. forests. “We are trying to be ahead of the movement of the pathogen.”

Olatinwo cautions that while laurel wilt is mainly affecting the southeastern U.S. now, sassafras is present from Maine to Florida to Kansas, with a huge diversity of Laurel family plants in other parts of the world. Thus, this disease has potential to cause broader scale damage.

“If the climate is favorable and the host trees are available to attack, then that area is likely vulnerable to damage should the beetle and pathogen get there,” says Olatinwo.

Read the full text of the review article.

For more information, email Rabiu Olatinwo at rabiu.o.olatinwo@usda.gov.

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