She stands proud and beautiful, more than just an ornamental piece of the landscape, but an iconic symbol of a state originally named for its natural floral affinities. The Sabal Palm resides at the biological crossroads of form and function: A marker of this state’s gateway to the tropics and a vegetative conduit for human sustenance. Of all palms in this state, the Sabal stands out as Florida’s emblem, a logo more significant than either the orange, live oak, or the conch shell due to its character, history, and sheer volume.
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The Sabal not only represents Florida, it is Florida, or at least the Florida God created and nature molded for hundreds of millennia. Just as mankind quickly chisels away Florida’s natural beauty in favor of pavement and cookie-cutter housing communities, so is the Sabal Palm falling to an intruder of a different kind.
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Like Florida’s natural charms carved from its flora and fauna, the Sabal tree is in peril, in many ways a metaphor for what is happening to this state. At an alarmingly rapid rate, Sabal palms, and over 21 other palm varieties, are falling ill via a particular horticulture grim reaper known as lethal bronzing disease.
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In 2006, lethal bronzing was identified in Florida for the first time and first isolated from a variety of different date palms. In 2008, lethal bronzing-causing bacteria was found in the Sabal Palm and cases of the disease have been identified in over 30 counties in Florida, including Marion, in which it was first discovered in August of 2019. In just five years from 2008 to 2013, lethal bronzing had spread from just three Florida counties to over 20. Though mostly concentrated in the central part of the state, the disease’s rapid spread is cause for concern over the entire state.
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“In 2016, you didn’t see this condition as far south as Palm Beach County,” said Dr. Brian Bahder, a researcher with the University of Florida Institute of Food and Agricultural Sciences (IFAS). But today, the disease has spread so fast that is likely the entire state will be engulfed soon. The situation is an eerie reminder of greening that has brought the Florida citrus industry to its knees.
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In the case of lethal bronzing disease, a type of bacterium called phytoplasma lives in the part of the palm where sap is transported. When piercing-sucking insects, such as leafhoppers, suck on the sap of the tree, they then become vectors of the disease to other plants. Most exasperating for researchers is that phytoplasma has no cell wall which makes it impossible to grow in a lab.
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Right now, once a tree becomes infected with lethal bronzing, the results are pretty grim. “There is no way to save a palm once it is infected,” Bahder said. “All that can be done is take steps to prevent the spread and future infection of nearby palms. Infected palms should immediately be removed from any other surrounding palms.”
What is lethal bronzing?
Like all other plants, the Sabal Palm has fruit, which is affected by lethal bronzing along with the fronds. If a palm has fruit present, the first noticeable sign of lethal bronzing is premature fruit drop, an easy indicator. But, a tree absent of fruit or flowers makes it especially hard to spot lethal bronzing, making the management of infected and nearby palms extremely difficult and adds to the spreading of the disease.
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After premature fruit drop, the most noticeable sign of lethal bronzing is leaf discoloration, hence the name of the disease. Unlike normal and natural leaf deterioration, lethal bronzing presents itself in a reddish, brown color. By contrast, a typical dying frond will appear gray in color. According to IFAS literature, symptoms of lethal bronzing take 4-5 months to become observable, but within 2-3 months after the tree is infected it dies. Simply removing dead fronds from the tree will not save it.
What can be done?
Because death is certain once symptoms begin to appear, the only answer is to remove the tree – antibiotics will not reverse the condition. “Prevention is the first line of defense,” Bahder says. “Our current recommendation for palms that test positive is to rip it out and either mulch it or burn it immediately.”
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Though only preventative measures can be taken, the industry is seeing rehabilitation through the administration of an antibiotic that protects against lethal bronzing. Called Oxytetracycline hydrochloride (OTC-HCI), the antibiotic is injected into the tree with continued administration every 3-4 months. For now, the OTC-HCI kit costs $495 and is being used mainly by nurseries and landscapes with a large number of trees.
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Not all hope is lost: Bahder and his team at UF released breakthrough research that may highlight a turning point in the management and control of the disease. They found that infected palms emit chemical signals, called volatile organic compounds, that warn nearby healthy palms of the disease threat. These compounds are used to indicate to other plants that they are stressed.
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“The threatened palms produce a compound with known antimicrobial properties, and we are now interested in how this affects the epidemiology of lethal bronzing in the field,” Bahder said. Though the compounds have been detected, the method of harnessing them for plant medicine has not yet been discovered.
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“The goal is to find cost-effective ways to protect palms whether they are over large areas that may be at risk or on individual properties. Ultimately, we want to cut down on time and resources for nurseries and consumers.”
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One of those methods is to place yellow sticky traps in the canopy of palms that are accessible from the ground. This method has been known to capture 300 adult individuals in a two-week time. In capturing nymphs, a Berlese funnel is used where clumps of grass and a thin layer of dirt are dug up and placed upside down in the funnel. There, a light is turned on to heat the sample and as the grass dries, the nymphs try to escape and fall downward into a container holding ethanol.
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In Florida, the palm tree industry is valued at over $400 million and Bahder estimates the losses due to lethal bronzing in the hundreds of millions of dollars as entire nursery plots have been wiped out. In addition, tree removals also result in losses of property value.
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In response, landscaping companies have begun to offer quarterly antibiotic injection contracts to coincide with the sale of palms. Though this may make up for losses in the industry, it also presents an added cost annoyance for consumers who may prefer options other than the state tree. This option may then lead to even less Sabal Palm trees in the state that embraces it as its own.
Where did it come from?
No definitive conclusions have arisen as to the nature of the disease or why and how it came here. It is believed to have originated in Jamaica before making its way to Florida. Bahder, though, has his theories.
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“What I think is going on is the insect that transmits the disease is native,” Bahder said. “Either hurricanes or strong weather patterns are bringing in populations of this bug that we have here naturally. But they’re bringing it from areas where the disease is spreading, so this allows the pathogen into the U.S.”
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The bug in question is the Haplaxius crudus (common name American palm cixiid), which belongs to a group of insects known as planthoppers.
Today, a drive down U.S. 441 is marred by matchsticks that used to be vibrant Sabal Palm trees. Where the symbol of Florida’s warm climes and carefree attitudes once welcomed natives and tourists alike to its unique charms, now ghastly carcasses stand as a harbinger of what may be ahead for Florida. Countless acres of citrus groves replaced by black rooftops, roadside country diners replaced by strip plazas and now the state’s symbol falling to a bug carrying deadly bacterium. Though this latest problem was not caused by man, it looks like it will be up to man to solve it.