Lethal bronzing in palms

What is lethal bronzing?

Lethal bronzing (LB) is a fatal palm disease caused by a phytoplasma that lives in the palm's phloem, the tissue that moves sap. It was first found in Florida near Tampa in 2006 and has reached more than 30 of the state's 67 counties. It is confirmed in 21 palm species, and no species has been confirmed resistant. Once a palm is infected, it dies.

2006

First found in Florida, near Tampa

30+

Of the state's 67 counties reached

21

Palm species confirmed as hosts

0

Species confirmed resistant

How does it spread?

Lethal bronzing moves one way: a planthopper called the American palm cixiid (Haplaxius crudus). The insect feeds high in the canopy, picks up the phytoplasma from an infected palm, and carries it to the next one. It does not move through soil, pruning tools, or wind. A palm can be infected and show nothing for three to five months, and UF/IFAS research has documented palms testing positive nine to twelve months later. For that whole time the palm feeds the insect and spreads the disease.

How do I spot it? The symptom sequence

Symptoms show up in order, from the bottom of the canopy up. First, premature fruit and flower drop, with flower stalks blackening. Next, the oldest lower fronds turn a reddish bronze (not yellow, not gray) and droop. The bronzing then climbs the canopy and the crown thins. Last, the spear leaf, the newest unopened center frond, collapses. When the spear goes, the heart of the palm is dead and there is no recovery.

Which palms are most at risk?

Across Southwest Florida landscapes, the most lethal bronzing deaths show up on Sabal (cabbage) palm and coconut palm, then the Phoenix group: Sylvester, Canary Island date, and true date palm. Queen, pindo, Mexican fan, foxtail, and Christmas palm are documented hosts with fewer field cases here. Bismarck palm is on the host list, but we have seen almost no confirmed cases on our properties, so we treat it as low risk. A Bismarck with symptoms still goes to the lab before any lethal bronzing step. No palm is confirmed resistant.

One Canary Island date palm we were called to sat at a community entrance. Its lower fronds were browning, and the crew caring for it, with the best intentions, thought it needed water. A sample went to a UF/IFAS lab. It tested positive for lethal bronzing.

That is the risk when nobody is watching palms with this disease in mind. Water would not have changed the outcome, and every week the palm stood, it fed the insect that spreads it.

Why speed matters

An infected palm does two things at once: it dies, and it feeds the insect that spreads the disease. Every day a confirmed-positive palm stands, planthoppers can carry the phytoplasma to the next palm on the property. That is why a confirmed positive should be tested and removed promptly. The removal decision is a licensed call that a Ptolemy arborist makes.

The one mistake to avoid

The common pitch is to inject every palm with an antibiotic every few months as standing prevention. Ptolemy does not run blanket quarterly injection across a property. Palms are monocots and cannot wall off a drill hole the way a tree does, so every injection is a permanent wound that adds up over years. Worse, an antibiotic can slow the symptoms of an already-infected palm, which leaves it standing and feeding the insect longer. That keeps the infection source on site, which is the opposite of control.

What you should do

You are the early-warning layer. Notice the early signs, photograph the whole palm and the symptom area, note the location, and report it. Do not let a suspected palm sit for weeks. Confirmation comes from a trunk core tissue test run by the UF/IFAS lab, not from a visual call. A symptom that looks like lethal bronzing is worth testing. It is not a diagnosis until the lab says so.