Florida's iconic palm trees threatened by invasive disease

DAVIE, Fla. — Florida's iconic palm trees are under attack from a fatal disease that turns them to dried crisps in months, with no chance for recovery once they become ill.

Spread by a rice-sized, plant-hopping insect, lethal bronzing has gone from a small infestation on Florida's Gulf Coast to a nearly statewide problem in just over a decade. Tens of thousands of palm trees have died from the bacterial disease, and the pace of its spread is increasing, adding to environmental woes of a state already struggling to save its other arboreal icon, citrus trees, from two other diseases.

Florida's official state tree – the tall, broadleafed sabal palm – is especially susceptible and Florida nurseries, businesses and homeowners are taking a financial hit as they scrap infected palms. Some preventive measures can be taken, but once infected, uprooting the tree is the only practical solution.

"Getting this disease under control is essential because it has the potential to drastically modify our landscape," said Brian Bahder, 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 said, "I don't think all the palm trees will die, but the issue we see will get a lot worse before it gets better."

Lethal bronzing, which experts say likely originated in Mexico, also is found in parts of Texas and throughout the Caribbean. Some worry it will migrate to California and Arizona, infecting date palms and damaging that fruit crop.

Coincidentally – but conveniently – lethal bronzing is attacking palms right outside Bahder's office at the University of Florida's agriculture research station near Fort Lauderdale. Some are dying, some are dead. This gives him a lab to test ideas and make presentations, so he is not removing infected trees as recommended.

"To understand the disease, I need to watch it spread and see what it is doing," said Bahder, an assistant professor with UF.

Lethal bronzing's first Florida appearance came near Tampa in 2006, but it's now found from the Keys in the south to Jacksonville in the north. The disease is transmitted solely by the haplaxius crudus, a tiny winged insect sometimes called the American palm cixiid or, generically, a treehopper. These specific treehoppers (there are other kinds) inject the bacteria through their saliva when feasting on the sap from a palm's leaves.

Once inside a tree, the bacteria migrate to its base, multiplying until they clog the circulatory system – much like human arteries getting blocked by fat and cholesterol. The blockage makes it impossible for the tree's cells to get sufficient nutrients and sugars, starving them. As an infected tree dies, its fronds and central spear leaf transform from green to a tell-tale shade of bronze as it succumbs in about six months. The disease doesn't infect humans or animals.