Palm Trees vs Lethal Bronzing: Discovery of Disease Signals Could Help Save the Plants

Palm trees are iconic symbols of Florida's tropical beauty and diversity.

However, a deadly disease called lethal bronzing is threatening to wipe out many palm species across the state. 

What is Lethal Bronzing and How Does it Spread?

(Photo : ASAAD NIAZI/AFP via Getty Images)

Lethal bronzing is a disease caused by phytoplasma, a unique type of bacteria that lacks a cell wall and is difficult to culture in a lab, as per Naples Botanical garden.

It is closely related to the strain that causes lethal yellowing in palms, another fatal disease that has affected palms in Florida and other regions.

Lethal bronzing affects about 19 palm species, including date, Canary Island, queen, cabbage, pindo and coconut palms.

It was first encountered in Hillsborough County in 2006 and has since spread to more than 30 of Florida's 67 counties.

The disease is transmitted by a piercing-sucking insect called the palm cixiid (Haplaxius crudus), which feeds on the sap of infected palms and then carries the bacteria to healthy palms.

The insect can fly up to half a mile and can infect palms year-round.

What are the Symptoms and Effects of Lethal Bronzing?

The first symptoms of lethal bronzing are early fruit drop or flower blackening (necrosis).

If flowers or fruit are not present, it can be difficult to notice this disease in its earliest stage.

The next symptom is leaf discoloration, starting with the oldest leaves and progressing upward. The foliage turns a bronze-like brown and dries.

This symptom is called bronzing.

The final symptom is the death of the topmost leaf, also called the spear leaf. This signals the death of the palm's apical meristem, or "heart."

The palm's decline will continue until it collapses or is removed.

Lethal bronzing can kill a palm within three to five months after infection.

It can also affect the ecological and economic value of palms, as they provide habitat, food, shade, aesthetic appeal and tourism attraction.

Also Read: Almost 50% Of Worldwide Palm Trees Are at Risk, Will Its Extinction Affect Biodiversity?

How to Prevent and Manage Lethal Bronzing?

Unfortunately, there is no cure for lethal bronzing once a palm is infected.

The only way to prevent the spread of the disease is to remove and destroy infected palms as soon as possible. This can reduce the source of inoculum for the insect vector and protect nearby healthy palms, as per Phys.org.

Another preventive measure is to inject healthy palms with antibiotics such as oxytetracycline (OTC) every three to four months.

This can suppress the bacteria and delay the onset of symptoms.

However, this treatment is costly, labor-intensive, and not guaranteed to work.

A recent study by the University of Florida scientists has revealed some promising findings on how palms can defend themselves against lethal bronzing.

The study found that infected palms emit signals that warn nearby healthy palms of the threat. Those healthy palms then produce their own defense that reduces their susceptibility to infection.

The researchers hope that this discovery can lead to new ways of enhancing palm resistance and saving Florida's landscape from lethal bronzing.

Related article: More Than Half of a Thousand Palm Tree Species at Risk of Extinction