It’s called lethal bronzing, and despite the name, it has nothing to do with ill-advised tanning practices. According to an Associated Press story, it’s a bacterial disease that’s killing off Florida’s iconic palm trees. Especially susceptible is the tall, broad-leafed sabal palm, the official state tree. The disease’s first appearance in the Sunshine State was in Tampa in 2006, and it’s now found from the Keys in the south to Jacksonville in the north.
Lethal bronzing is a bacterial disease that’s spread via the American palm cixiid, a rice-sized winged insect with the scientific name haplaxius crudus, commonly known as a treehopper. There are many other treehoppers, but this specific species injects the bacteria through its saliva as its sucks sap out of the palm trees’ leaves. Once the bacteria is inside the tree, any palm cixiid that later feeds from an infected tree will pick up the infection and pass it along to another palm.
The bacteria kill the tree by clogging its arteries. The bacteria travel to the tree’s base and multiply there, creating a barrier that makes it impossible for the tree’s cells to draw up nutrients and sugars. The tree essentially starves to death.
As an infected tree dies, its fronds and central spear leaves turn from green to bronze, with death occurring in about six months. Once infected, there’s no cure. Some preventive measures can be taken, but once a tree is infected, the only solution is to uproot it. Scrapping all the infected trees has inflicted a big financial burden on Florida homeowners, nurseries and other green industry companies.
There is concern that the malady will migrate to California and Arizona and damage the date crop. It’s already taken a heavy toll on Jamaica’s coconut plantations. Brazil is taking preventive measures to keep the vector insect out.
Tens of thousands of palm trees have already died, and the pace of spread is increasing. This adds to the burden on a state already struggling to save its citrus trees from two other diseases.
“Getting this disease under control is essential because it has the potential to drastically modify our landscape,” says Brian Bahder in the story. He’s an entomologist who studies insect-borne plant diseases and is a leader in the state’s battle against lethal bronzing. If nothing is done, Bahder says, “I don’t think all the palm trees will die, but the issue we see will get a lot worse before it gets better.”
Bahder’s been able to conduct research from the window of his office at the University of Florida’s agriculture research station near Fort Lauderdale. Right outside, lethal bronzing is attacking some palms. Some are dying, others are already dead. The assistant professor uses this stand as a lab where he can test ideas and make presentations, so he’s not removing infected trees as is recommended.
“To understand the disease, I need to watch it spread and see what it’s doing,” Bahder told the AP reporter.
Genetic testing shows the disease likely originated in Mexico’s Yucatan region. Bahder’s hypothesis is that 2005’s Hurricane Wilma blew infected bugs across the gulf; others hitched rides on vehicles. He was quoted as saying that the palm cixiid is attracted to white cars.
The state agriculture department regularly inspects palm nurseries and certifies those found to be disease-free. Infected trees are compounded and destroyed, and any remaining palms are quarantined for at least six weeks. Calls to about a dozen palm tree farms around the state weren't returned, according to the story. Bahder said it is a problem tree farm owners don’t like to discuss publicly, fearing it will hurt business.
Eric Muecke, Tampa’s urban forestry manager, told the AP that the city has had success containing the disease by keeping its palms healthy and surrounding the more susceptible palm varieties with trees that don’t attract the bugs.
“It’s not like it marches through a tree population — you don't see one dead tree after another,” Muecke is quoted as saying. “It hops around; it’s pretty sporadic.”
Brent Gaffney, a Gainesville landscaper, says Bahder’s research is the state’s best hope for containing the disease, but only if he gets enough funding. Studies are underway on whether massive doses of antibiotics can save trees in the infection’s early stages.
According to the story, after infected trees are removed, nearby palms need preventive antibiotic injections to avoid getting the disease themselves. But these injections are pricey — each one costs $50 and loses effectiveness after three months, putting them out of the reach of most homeowners, Bahder is quoted as saying. Only high-end resorts that use mature palms to enhance ambience might consider injecting trees without a nearby infection.
Lethal bronzing was dubbed “Texas Phoenix palm decline” when it appeared in that state in the late 1970s, killing trees in the Rio Grande Valley around Brownsville. Texas’ agriculture department says outbreaks today are infrequent and isolated — but Bahder told the AP reporter that global warming is widening the threat.
“With increased human movement around the region and especially, stronger weather patterns in regards to climate change, there are more possible routes for invasive insects,” Bahder says.