Lethal Bronzing Disease (LB)

The disease was originally known as Texas Phoenix Palm Decline (TPPD) due to its first discovery in Phoenix palms in Texas. Lethal bronzing disease (LB) is a devastating bacterial disease affecting various palm tree species, including coconut palms, date palms, and Canary Island date palms. The disease is caused by a bacterium called phytoplasma, which is spread by a tiny insect called the planthopper.

Pathogen 

The lethal bronzing disease is caused by phytoplasma, a type of unculturable bacteria lacking a cell wall. The specific phytoplasma that causes LB has been classified as "Candidatus Phytoplasma aculeata." This pathogen is transmitted by a tiny insect called the planthopper, which feeds on the sap of infected palm trees and spreads the bacteria as it moves from tree to tree. The lack of effective treatments or cures for LB makes prevention and early detection crucial for managing and controlling the disease.

Phytoplasmas are specialized bacteria that live in the phloem tissue of plants, where they obtain their nutrients and reproduce. They are typically transmitted to other plants by piercing-sucking insects, such as planthoppers, leafhoppers, and psyllids, which feed on the sap of infected plants and acquire the phytoplasmas in the process. The insects then transmit the phytoplasmas to healthy plants as they continue to feed, spreading the infection from plant to plant.

Symptoms 

The first symptoms of lethal bronzing disease (LB) can vary depending on the species of the palm tree and the stage of infection. However, if the tree is bearing fruit, the first symptom is often premature fruit drop, which can occur as early as six weeks after the onset of symptoms. Other early symptoms of LB can include yellowing or browning of lower leaves, discoloration of the fruit stalk, and wilting of new growth. As the disease progresses, the symptoms become more severe, with the tree's entire canopy turning brown and dying back. In some cases, LB can lead to the tree's death within six months to a year after the initial symptoms appear.

Early detection and prompt treatment are critical for managing the spread of LB and preventing the loss of valuable palm trees. The time duration between infection with the lethal bronzing disease (LB) phytoplasma and the development of symptoms, known as the latent period, is variable and can depend on several factors. However, research suggests that the latent period for LB is approximately four to five months. During this time, the phytoplasma multiplies within the host plant and spreads throughout the phloem tissue. As the infection progresses, the phytoplasma interferes with the plant's ability to transport water and nutrients, which can lead to the characteristic symptoms of the disease, such as leaf yellowing, fruit drop, and overall decline.

Host Range and Distribution 

Lethal bronzing disease (LB) has been found in at least 21 different species of palm, including several commonly cultivated in Florida, such as the coconut palm, queen palm, and date palm. The disease was first identified in Florida in 2006, and since then, it has spread to several counties in the state, as well as to parts of Texas and Mexico. As LB continues to spread, it could potentially infect a wider range of palm species in affected areas, especially as it moves further south into areas with higher palm diversity. This highlights the need for ongoing surveillance and monitoring of the disease in affected regions, as well as efforts to prevent its spread to new areas through measures such as quarantine, insect control, and removal of infected palms.

Managing LB 

The management of lethal bronzing disease (LB) currently involves a combination of strategies, including the removal of infected palms and preventative measures such as injecting palm trees with antibiotics. The antibiotic oxytetracycline-hydrochloride has been used for this purpose, but studies have shown that once LB symptoms are visible, the oxytetracycline-hydrochloride label rate is insufficient to reverse the symptoms.

Therefore, early detection of LB and prompt treatment with antibiotics before symptoms become visible is crucial for effectively managing the disease. Additionally, other preventative measures, such as controlling insect vectors that spread the disease and avoiding the movement of infected plant material, can also help to slow the spread of LB. Ongoing research is also being conducted to develop new management strategies for LB, including using alternative antibiotics and genetic approaches to improve the resistance of palm trees to the disease.

Even if no symptoms of lethal bronzing disease (LB) are present in a palm tree, it may still be infected with the phytoplasma that causes the disease. Since the latent period of LB is around four to five months, there may not be sufficient time for the antibiotic to take effect before symptoms develop.

Therefore, it is recommended to remove infected palms even if no symptoms are visible, as well as to test healthy-looking palms to identify which ones are not infected and start preventative injections with antibiotics. This can help slow the spread of the disease and prevent further infections.

It's important to note that removing infected palms should be done carefully to avoid spreading the disease to other palms in the vicinity. Additionally, proper disposal of infected plant material is essential to prevent the spread of LB to new areas.

Conclusion

In conclusion, Lethal Bronzing Disease (LB) is a serious threat to palm trees in Florida, the Caribbean, and Mexico. It is essential to take action to prevent the further spread of this devastating disease and protect our valuable palm tree populations. By following proper management techniques and remaining vigilant for signs of LB, we can help preserve the beauty and health of our palm trees for future generations. Down To Earth Landscape & Irrigation has effective solutions for LB disease. Contact us for more information.