Lethal bronzing is an emerging palm disease

Lethal bronzing of palms is a relatively new disease to the southeastern United States affecting several palm species. As the name describes, it eventually kills the tree.

Lethal bronzing is caused by a bacterial phytoplasma which is spread from infected trees to healthy trees by a sap-feeding plant hopper. Testing is underway to determine exactly which of Florida’s plant hoppers can spread the disease. The primary suspect insect is Haplaxis crudus, which is found throughout Florida and the Caribbean. The pathogen was first discovered in Texas killing Phoenix palms, so it was called Texas Phoenix Palm Decline or TPPD. Because the disease is now widespread and is killing a variety of palm trees including native sabal palms, the name was changed to better describe the current situation and the reddish color symptoms of dying fronds.

It was initially thought that infected trees were being moved from Texas into Florida and then the disease was spread locally by native plant hoppers. Dr. Brian Bahder, assistant professor with the UF/IFAS Fort Lauderdale Research and Education Center, is studying the disease and the insect(s) that help spread it. He hypothesizes that the insects with the pathogen were blown in from the Yucatan Peninsula in 2005 by Hurricane Wilma due to the fact that Hurricane Wilma’s track first took it over the Yucatan, and then into Florida’s Gulf counties. The disease first appeared in Florida in 2006 in the hurricane-impacted counties of Hillsboro, Manatee and Sarasota.

The pathogen is now killing trees in more than 31 Florida counties, including nearby St. Johns, Duval and Volusia. The plant hopper suspected of spreading the disease is also native to the Yucatan, but Dr. Bahder thinks our native population didn’t have the disease. Genetic testing is underway to try to prove where the infected insects came from. This could help develop better management strategies. Humans can also play a role by moving infected palms and plant material harboring plant hoppers. The immature life stage of the Haplaxis crudus feeds on young turfgrass shoots, and this means shipments of turf from areas impacted by lethal bronzing could transport phytoplasma carrying insects into new areas.

To date, the disease is primarily affecting Phoenix palm species including true date palm, Canary Island date palm, pygmy date palm and wild date palm. Also affected are native sabal palms, queen palms and Chinese fan palms. New hosts are being added as the disease spreads into areas with more palm diversity. The disease starts as bronzing of the lower leaves with an upper layer of fronds that stay green, and the middle spear leaf eventually dies. A ring of green leaves may persist for a number of months. There is a similar pathogen in South Florida called Lethal Yellowing that affects most non-native palms. To have a pathogen on the move that can kill our state tree, the Sabal palmetto, is very unnerving.

There is a test to confirm the pathogen by collecting tissue from the trunk. Positive or obviously symptomatic trees should be removed. There is no cure for this disease, but a tried and tested preventative treatment has been used for years to protect palms from Lethal Yellowing and now seems very effective to protect palms from Lethal Bronzing. The treatment involves injecting the trees preventatively with the antibiotic oxytetracycline. Applications of products should be done by professionals knowledgeable in the International Society of Arboriculture tree injection best management practices. 

Sol Looker is the Residential Horticulture Extension Agent and Master Gardener Coordinator at the Flagler County Extension Service, University of Florida. For more information contact the office, 386-437-7464. The Extension Service is located at 150 Sawgrass Road, Bunnell.