Lethal Bronzing and Palm Trees: Causes, Symptoms, and Prevention

A deadly disease has killed hundreds of the Sunshine State’s beloved palm trees, including Florida’s state tree, the sabal palmetto palm. Called lethal bronzing disease, it started affecting Jacksonville palms in the past decade. 

This palm tree killer gets its name because of its most striking symptom: It turns palm fronds bronze-brown before eventually killing the tree.

Lethal bronzing used to be called Texas Phoenix Palm Decline (TPPD) because it was first discovered infecting trees from the Phoenix genus of palms in Texas. However, it’s no longer an accurate name, as it has reached Louisiana and Florida and affects at least 21 palm tree species.

Learn how to spot and prevent lethal bronzing in your own Jacksonville trees in this article. 

This article covers:

• Lethal Bronzing’s History in Florida
• Cause of Lethal Bronzing
• Symptoms of Lethal Bronzing
• Management
• How to Prevent Lethal Bronzing
• FAQ About Lethal Bronzing

Lethal Bronzing’s History in Florida

Lethal bronzing was first discovered in Florida in 2006 in Hillsborough, Manatee, and Sarasota counties in West Central Florida. By 2013, it had already killed palm trees here in Duval County. As of 2022, arborists have found that the disease has spread to 36 of the Sunshine State’s 67 counties.

Jacksonville seems to be the northernmost city affected for now, and it has spread as far south as the Keys.

Larry Figart is an urban forestry extension agent for UF/IFAS (University of Florida Institute of Food and Agricultural Sciences) Extension Duval County. He says several things have happened to increase the alarm about this deadly disease. “The number of counties of record expanded, they found the vector that carried it, and they increased the number of host palms,” he says.

The disease is spreading throughout Northeast Florida and is prolific in Tampa and St. Petersburg. Figart remarks that lethal bronzing may have made its way to Jacksonville thanks to newly planted trees brought in from the Tampa area.

Cause of Lethal Bronzing

Figart says there is still a lot we don’t know about lethal bronzing. He says researchers do know what insect is responsible for spreading it. “We just found out [in 2021] what the insect is,” he says.

The insect is a planthopper insect called the palm cixiid (Haplaxius crudus). This tiny insect is yellow-olive in color with transparent wings. Figart says these pests suck the sap of infected trees, then move to feed on another tree, spreading the disease.

Researchers suggest that the palm cixiid may have come from the Caribbean in the early 1900s, hitching a ride on imported palms. The palms may have been carrying plant diseases way back then.

However, the insect itself doesn’t cause lethal bronzing; it only spreads it. The disease is actually caused by phytoplasmas, which are a type of bacteria without a cell wall. Because of its lack of a cell wall, it’s difficult to study in a lab.

The phytoplasma is closely related to the phytoplasma that causes lethal yellowing, another deadly palm disease affecting more than 30 types of palm trees in South Florida. These phytoplasmas don’t seem to be able to spread through tools, as they can only survive in sap and insects.

Symptoms of Lethal Bronzing

Jax homeowners won’t notice any symptoms until 4 to 5 months after their beloved palm has been infected. Fruits will start dropping to the ground much earlier than expected. Then, the palm’s flowers start dying. 

If your palms don’t have fruit or flowers, the first symptom you’ll observe is lethal bronzing’s most prominent one: The oldest leaves will start turning bronze, brown, or gray. The disease will work its way up to the younger fronds until it reaches the spear leaf.

If your palm’s spear leaf has collapsed, then your palm is completely dead.

From the first sign of disease, your palm has about 2 to 3 months left to live.

This happens because the phytoplasma concentrates in the palm’s sap at the base of the tree and cuts off its circulatory system. Associate Professor Dr. Brian Bahder of the UF/IFAS describes it as being like a heart attack. “The blood vessels are just clogging up, and the palm can’t handle it, and it dies,” he says.

Management

Like its name suggests, lethal bronzing is a death sentence for your palm trees, even before they start showing symptoms. For now, it’s even deadlier than lethal yellowing, which can be cured with and has been curbed by antibiotic injections.

Once your palm starts showing signs of lethal bronzing, it should be removed to prevent the disease from spreading. Then, test the neighboring trees for lethal bronzing; contact your county’s UF/IFAS Extension office for help.

Any trees found to test positive for lethal bronzing should be removed from your property. 

How to Prevent Lethal Bronzing

You can also inject your healthy palm trees with antibiotics to prevent lethal bronzing. This involves injecting them with oxytetracycline-hydrochloride (OTC) every 3 to 4 months for at least two years.

However, there are downsides to this preventative treatment.

First, it can get expensive if you have a lot of trees to treat.

UF/IFAS’ Figart says the injections can also do lasting damage to your palm trees. The injections scar the trees, and palms don’t heal as quickly as other trees. “You’ll see every single injection site. You’re wounding the tree,” he says.

Figart recommends treating your trees only if the disease is in your neighborhood. “That means the vector is around. If it’s not nearby, there is no reason to inject your trees.”

FAQ About Lethal Bronzing

How to Keep Your Jacksonville Trees Healthy

Jacksonville lawns have more trees than just majestic palms. Maintaining these towering beauties is well worth the effort, but not everyone has the time or energy to do so. If you’re one of these busy homeowners, connect with a Jacksonville tree care professional to handle all your tree care needs for you.

Main Photo by: James St. John / Wikimedia Commons / CC BY 2.0

Janine Caayao

Janine Caayao has always been fascinated with growing plants, from fruits and veggies to bonsai trees and orchids. Now, she’s interested in urban gardening with her family. She loves finding new tips and tricks to keep their plants thriving.

Posts by Janine Caayao