The tree doctor's guide to Florida palm disease.

Florida is losing palms faster than it is planting them, and two diseases account for most of the decline we diagnose in the field: Lethal Bronzing (a phytoplasma) and Ganoderma Butt Rot (a wood-decay fungus). Both are widespread, both are frequently misdiagnosed, and one of them is contagious. Knowing the difference is the first job of any property owner with mature palms on the lot.

What follows is the diagnostic framework our arborists use on a field visit. It is written for owners who want to understand what they are looking at — and what is actually treatable.

Lethal Bronzing (Candidatus Phytoplasma palmae)

Lethal Bronzing — formerly called Texas Phoenix Palm Decline — is a phytoplasma disease spread by planthopper insects. It infects the phloem and shuts down the palm's vascular system from the inside. Once symptomatic, the palm is dying. There is no cure; there is only confirmation and management.

Susceptible species in Florida

• Sabal palmetto (cabbage palm — Florida's state tree)
• Phoenix canariensis (Canary Island date palm)
• Phoenix dactylifera (date palm)
• Phoenix sylvestris (silver date palm)
• Syagrus romanzoffiana (queen palm) — increasingly affected
• Bismarckia nobilis (Bismarck palm) — newer host

Field symptoms, in order of appearance

1. Premature fruit drop — entire infructescences abort before ripening.
2. Flower necrosis — emerging inflorescences turn black and die.
3. Discoloration of the oldest (lowest) leaves — bronzing from tip inward, not the uniform yellowing of nutrient deficiency.
4. Death of the spear leaf — the youngest unopened frond collapses or pulls out cleanly. This is the diagnostic endpoint.
5. Crown collapse within 3–5 months of spear death.

Confirmation and management

Lethal Bronzing is confirmed by qPCR testing of trunk core samples at a diagnostic lab (the University of Florida runs the standard assay). On high-value palms in proximity to confirmed cases, preventive oxytetracycline (OTC) trunk injections every 3–4 months can suppress the phytoplasma in uninfected palms, but they cannot cure infected ones. The protocol is a long-term commitment, and the moment injections stop, susceptibility returns.

The hard truth: removal of confirmed infected palms is the most important intervention. Each symptomatic palm is a reservoir for planthopper transmission to every susceptible palm within flight range.

Ganoderma Butt Rot (Ganoderma zonatum)

Ganoderma is a wood-decay basidiomycete that infects the lower trunk of palms. It is soil-borne, host-specific to palms, and untreatable. Unlike Lethal Bronzing, it spreads through spores released from a visible fruiting body (conk) on the lower trunk, not by an insect vector.

Field symptoms

• Generalized canopy decline — older fronds yellow and droop, new fronds emerge smaller and pale.
• Trunk discoloration — a darkened, often water-soaked band on the lower 4 feet of trunk.
• Conk emergence — a shelf-like, varnished, reddish-brown fruiting body on the lower trunk, often near the soil line. This is diagnostic; conks usually appear late in the disease cycle.
• Internal trunk decay — the trunk becomes structurally compromised long before the canopy fully collapses. This is a hazard tree.

Confirmation and management

Conk presence is diagnostic. In the absence of a visible conk, trunk coring and lab culture can confirm. There is no chemical treatment. Removal is the only management option, and the spores persist in the soil — replanting a palm in the same hole is contraindicated. We recommend a hardwood replacement or a 24-month soil rest.

What is NOT Lethal Bronzing or Ganoderma

Most palm decline we are called out to assess is not disease — it is nutrient deficiency, transplant stress, or improper pruning. Common look-alikes:

• Potassium deficiency — translucent yellow-orange spotting on oldest fronds, frizzled tips. Treatable with controlled-release sulfur-coated potassium sulfate, NOT muriate of potash.
• Manganese deficiency ('frizzle top') — youngest fronds emerge weak, frizzled, and chlorotic. Treatable with soil-applied manganese sulfate.
• Boron deficiency — newest spear bent, hooked, or distorted. Treatable but easy to overdose; soil test first.
• Over-pruning — the 'hurricane cut'. Removing green fronds starves the palm of the nutrients it was actively translocating from old to new growth. Illegal in many Florida municipalities.

The Tree Rx diagnostic workflow for palms

1. Full property palm inventory by species, with GPS-tagged photos.
2. Crown and trunk assessment per palm — spear test, conk inspection, nutrient pattern read.
3. Soil sample at the root zone for nutrient panel and pH.
4. Lab confirmation (qPCR for Lethal Bronzing, culture for Ganoderma) on any palm where field symptoms are ambiguous.
5. Written prescription with priority tiers — confirmed disease (remove), at-risk (preventive OTC program), and nutrient-driven (amend and re-test in 90 days).

Palms are not interchangeable with trees in either diagnosis or treatment. They have a single growing point, no secondary growth, and no capacity to compartmentalize disease the way a hardwood does. The diagnostic window is short, the treatment options are limited, and the consequences of misdiagnosis are usually fatal to the palm. Get a real arborist on the property before you commission removal — or worse, before you commission injections that won't work.