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Florida’s famous palm trees threatened by disease

World News | Published:

The disease is spread by a rice-sized, plant-hopping insect.

Florida’s famous palm trees are under attack from a fatal disease

Florida’s famous palm trees are under attack from a fatal disease.

Spread by a rice-sized, plant-hopping insect, lethal bronzing has gone from a small infestation on Florida’s Gulf Coast to a nearly state-wide 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 the environmental woes of a state already struggling to save its other arboreal favourite, the citrus tree, from two other diseases.

Florida’s official state tree – the tall, broad-leafed sabal palm – is especially susceptible and Florida nurseries, businesses and homeowners are taking a financial hit as they scrap infected palms.

Some preventative 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.

Brian Bahder examines a palm tree that died from a lethal bronzing disease
Brian Bahder examines a palm tree that died from a lethal bronzing disease (Wilfredo Lee/AP)

If nothing is done, he 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.”

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Lethal bronzing, which experts say probably originated in Mexico, is also 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. The disease has already heavily damaged Jamaica’s coconut plantations, and Brazil is taking preventative measures to avoid invasion.

Coincidentally – but conveniently – lethal bronzing is attacking palms right outside Mr 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.

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“To understand the disease, I need to watch it spread and see what it is doing,” said Mr Bahder, an assistant professor.

Lethal bronzing’s first Florida appearance came near Tampa in 2006, but it is now found from the Keys in the south to Jacksonville in the north.

A plant-hopper insect
A plant-hopper insect, that is thought to transmit a lethal bronzing disease to palm trees (Wilfredo Lee/AP)

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 inject the bacteria through their saliva when feasting on the sap from a palm’s leaves. Any palm cixiid that later feeds from the tree will pick up the infection and pass the bacteria to more palms.

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 does not infect humans or animals.

Genetic testing shows lethal bronzing probably originated in Mexico’s Yucatan region.

Mr Bahder’s hypothesis is that 2005’s Hurricane Wilma, which tracked from the Yucatan to Florida, or a storm with a similar path, carried infected treehoppers across the gulf to Tampa.

Those insects infected the palms, which infected native treehoppers. The disease spread when winds blew infected bugs to new territories or they hitched rides on vehicles. Mr Bahder said the palm cixiid is particularly attracted to white cars.

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