If you’ve been told or suspect that your palm has lethal bronzing or lethal yellowing disease, what does that mean? What caused it? Is your palm tree dying? Can either disease be prevented? We answer those questions and more about these deadly diseases that kill palm trees in South Florida.
What is Lethal Bronzing Disease?
Lethal Bronzing Disease (LBD) is a bacterial disease of palms that first appeared in the Tampa area of Florida in 2006. Since then, LBD has spread to over 30 Florida counties and continues to spread. The original name of this disease was “Texas Phoenix Palm Decline,” but scientists changed its name as the disease spread to other states and other palm species. You’ll find LBD in Louisiana as well as Florida and Texas.
Science isn’t certain of the origin of LBD in South Florida, but its course of travel suggests that infection spread along hurricane routes by wind-borne insects.
Palm lethal yellowing on coconut palms, USDA Forest Service – Region 8 – Southern, USDA Forest Service, Bugwood.org.
Which palm species can be infected with Lethal Bronzing Disease?
LBD affects many of the palm species you’ll find in South Florida, including these familiar ones:
- Christmas Palm (Adonidia merrillii)
- Bismarck Palm (Bismarckia nobilis)
- Pindo Palm (Butia capitata)
- Carpentaria Palm (Carpentaria acuminata)
- Coconut Palm (Cocos nucifera)
- Chinese Fan Palm (Livistona chinensis)
- Canary Island Date Palm (Phoenix canariensis)
- Edible Date Palm (Phoenix dactylifera)
- Pygmy Date Palm (Phoenix roebelinii)
- Wild Date Palm (Phoenix sylvestris)
- Fiji Fan Palm (Pritchardia pacifica)
- Buccaneer Palm (Pseudophoenix sargentii)
- Mexican Palmetto (Sabal mexicana)
- Cabbage Palm (Sabal palmetto)
- Queen Palm (Syagrus romanzoffiana)
- Chinese Windmill Palm (Trachycarpus fortunei)
How does Lethal Bronzing Disease spread?
The bacteria that causes lethal bronzing is spread by leafhoppers and planthoppers, damaging insects that feed on plant sap. These insects attack palms (and other plant species) by biting into plant leaves (or palm fronds) and sucking out the sap.
Is there a cure for lethal bronzing in palms?
At this time, there is no cure for this palm disease and it’s always fatal (which is why it’s called Lethal Bronzing Disease).
What is Lethal Yellowing of palms?
Like LBD, Lethal Yellowing (LY) is a bacterial palm disease. The bacterium that spread lethal yellowing is very similar to the bacteria that cause lethal bronzing, but the two are scientifically distinct.
Scientists first identified LY in 2007, but unlike lethal bronzing, the yellowing disease is not as widespread in Florida. According to the University of Florida, the lesser spread of lethal yellowing is the result of careful monitoring, coconut palm removal, and preventive treatment.
Which palms are most affected by Lethal Yellowing?
LY is most devastating to coconut palms (Coco nucifera), which grow on shorelines in Florida and throughout tropic regions, and in plantations, where growers cultivate the palms for their fruit and for coconut oil.
While Lethal Yellowing has seriously damaged coconut palms, there are over 30 species of palms in Florida that are susceptible to LY. Many of the species are the same as in the list for Lethal Bronzing Disease above; you can find a full list at the University of Florida’s ag extension.
How does Lethal Yellowing spread?
Lethal Yellowing spreads the same way as Lethal Bronzing Disease – it’s carried by planthoppers that move from palm to palm and pierce palm fronds to reach their sap.
Will palms survive if they’re infected with Lethal Yellowing?
No. Like LBD, lethal yellowing is fatal and has no cure.
Spread & Transmission
How do these diseases infect and kill an entire palm?
All palms send sap down from their leaves (fronds) to the rest of the tree through their phloem tissue. You can think of it as the network of “arteries” that plants use to distribute food energy and water throughout their structure.
When feeding insects bite into leaves, they pass the LBD or LY bacteria from their saliva into the leaf. From there, the palm’s phloem system spreads it further into the palm.
Once either of the bacteria gets inside a palm there is no way to prevent them from killing the palm.
Can these palm diseases be spread through infected pruning tools or other methods?
These diseases are only transmitted by sap-sucking insects so there is no other way for them to spread. Disinfecting your tools and other standard sanitary practices won’t help stop LBD or LY. The bacteria that cause both diseases can’t survive on its own outside of a plant’s phloem system.
Lethal yellowing in palm trees, USDA Forest Service – Region 8 – Southern , USDA Forest Service, Bugwood.org.
Symptoms
What does Lethal Bronzing Disease look like?
How a palm tree shows symptoms of LBD depends on the age and condition of the infected palm:
- Older palms that are flowering and fruiting first show LBD in their dropped fruits and dead flowers
- Young palms that haven’t yet flowered and older palms without flowering stems show progressively dying leaves that die from the bottom of their crown to the terminal, or topmost, frond (or spear).
Can a palm have no symptoms but still be infected with lethal bronzing?
Your palms may have LBD for up to five months before symptoms start showing.
How quickly with lethal bronzing kill a palm tree?
After Lethal Bronzing Disease symptoms are visible, your palm will only live a few more months. Once you notice that the terminal frond is dead, that’s a sign that the palm has died.
NOTE: The symptoms and course of LBD varies among the species of palms affected by the disease, so these timeframes are best estimates.
Are the symptoms of Lethal Yellowing different from Lethal Bronzing Disease?
You can identify Lethal Yellowing in palms from a series of symptoms that progress as the disease progresses.
The symptoms of Lethal Yellowing are:
- Premature fruit dropping
- Diseased fruits that are blackened at their stem end
- Dying flower stalks that start out healthy and then turn black
- Fronds yellowing and dying, from the base of the crown to the top
- Dead fronds wilting and hanging down from the palm’s crown, then dropping
Treatment & Prevention
What can I do to stop Lethal Bronzing Disease and Lethal Yellowing?
Because there is no cure for either disease, we have to rely on prevention. Just like people, palms can carry a disease and show no symptoms but still transmit that disease.
We can save healthy palms (those with no symptoms of either disease) that are growing near infected palms by:
- Regularly testing to ensure healthy-looking palms are not carrying the diseases
- Regular injections of oxytetracycline HCl (an antibiotic), 3-4 times a year as a preventive measure
RESEARCH NOTE: All species of palms treated with antibiotic injections may remain free of these bacterial diseases but still become infected in the future. Currently there is no established timeframe for how long treated palms may be immune from further infection if the disease is still active where they are.
Can antibiotic treatment save infected palm trees?
Sadly, when a palm shows symptoms—even just the first symptoms—of Lethal Bronzing Disease it’s too late for anyone to save the palm.
In contrast, palms that show early symptoms of lethal yellowing may survive when given antibiotic treatment early enough.
Although there is not yet any guarantee that antibiotic injections prevent LBD or LY from attacking a palm, it is one of the two best preventive measures we have. The second measure is palm removal.
Do I need to remove palms infected with lethal yellowing or lethal bronzing?
Experts recommend removing all infected palms as soon as possible so that no bacteria spreads from them to other palms by sap-sucking insects. An infected palm is a host for both LY and LBD, and we need to limit the number of hosts for these diseases.
What should you do if you notice possible symptoms of either palm disease?
It’s up to all of us to notice and report any instance of Lethal Bronzing Disease or Lethal Yellowing that we see. If you think your palms have either of these diseases, call an arborist as soon as you can. It’s critical that if any of your palms have LY or LBD you have an arborist remove them to prevent the spread of these diseases to other palms.
We Can Help You
We have experience working on all the palm species in South Florida that are susceptible to lethal bronzing and lethal yellowing. If you are concerned about your palms, want to know more about testing and treating healthy palms, or need palms removed, give us a call. We’ve been caring for South Florida palm trees for over 40 years and we will gladly care for yours, too.
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Whether you're looking for specific tree care services, such as palm trimming, tree removal, or disease treatments, or would like one of our Arborists to examine your trees to identify any issues and recommend options, we're always here for you! Just give us a call at 954-788-4000 to set up an appointment.
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