A deadly and swift disease is attacking Florida’s beloved palm trees. It’s called lethal bronzing disease. It’s on the rise and in the past decade has invaded Jacksonville.
This palm tree killer gets its name because it turns palm fronds bronze or brown before killing the tree. It used to be called Texas Phoenix Palm Decline, or TPPD, after researchers discovered it in the coastal areas of Texas in the 1980s in palms in the Phoenix genus. They changed the name after the disease spread to Louisiana and Florida and started affecting more types of palm trees.
Lethal bronzing first appeared in Florida in Hillsborough County in 2006, and by 2013 had killed trees in Duval County.
Larry Figart is urban forestry extension agent for UF/IFAS (University of Florida Institute of Food and Agricultural Sciences) Extension Duval County. He says there is still a lot we don’t know about the disease. He says researchers do know an insect is responsible for spreading it. “We just found out last year what the insect is,” he says.
The insect is a planthopper called the palm cixiid. These tiny insects are tan with translucent wings. Figart says they suck the sap of infected trees, then move to feed on another tree, spreading the disease.
Arborists have found lethal bronzing in at least 31 counties in Florida, including trees in Jacksonville. The disease affects at least 16 palm species, including Florida’s state tree, the sabal palmetto palm. 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 (insect) that carried it, and they increased the number of host palms,” he says.
While lethal bronzing is present in Jacksonville and Duval County, Figart says it isn’t widespread yet. He says in the past five years, he’s only seen three cases. “I don’t want to say it’s not an issue in north Florida, but I don’t see it nearly as often as fusarium (another type of palm disease).” He says lethal bronzing is prolific in Tampa and St. Petersberg. He adds that lethal bronzing may have made its way to Jacksonville in newly planted trees from the Tampa area.
Cause and Symptoms
A bacteria-like phytoplasma causes lethal bronzing. The phytoplasma concentrates in the base of the tree and cuts off its circulatory system. This starves the tree of the nutrients it needs to survive. Fruit spikes, if present, will turn black and die.
Any palm fruits may drop prematurely. After that, older and lower fronds will start to turn bronze, brown or gray. Eventually, younger fronds and the palm’s central spear leaf will turn brown, then the tree dies. This process usually takes about four to five months.
Management and Prevention
Once a tree has contracted lethal bronzing, there is no way to treat it. To keep the bacterial disease from spreading to healthy trees, you must remove any infected palms. You can stay ahead of the disease by testing healthy trees. Any palm with a positive result should be removed.
You can also take the preventive step of antibiotic injections for healthy trees. Doing this involves injecting them with oxytetracycline-hydrochloride every three to four months for at least two years.
There are downsides to these treatments. First, they 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. He says 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.”
Lethal bronzing is closely related to another palm disease called lethal yellowing. Lethal yellowing affects more than 30 types of palm trees, including tall coconut palms, in South Florida. It is spread by a planthopper and causes palm fronds to turn yellow. Unlike lethal bronzing, lethal yellowing can be cured with antibiotic injections. There can still be isolated outbreaks of lethal yellowing. It’s not nearly as common as it used to be, possibly because of the antibiotic treatments.
While there is certainly cause for concern when it comes to lethal bronzing, it’s important to know that it’s not prevalent in Jacksonville or Duval County so far. That could change as it continues to spread north, so the best way to protect your palms is to stay aware of new outbreaks in your area.