LSU AgCenter Horticulturist
(11/13/20) If you enjoy a tropical look to your landscape, palm trees can provide it. Palm trees grow in tropical and sub-tropical climates, meaning they prefer higher temperatures. Luckily, south Louisiana has a sub-tropical climate, and most winters are relatively mild. Incorporating palm trees into your home landscape is a good possibility.
Palm leaves give these trees their unique look with exotic foliage and unique forms. Botanically speaking, the leaves are referred to as fronds. Fronds are typically very large, compound and evergreen, sitting atop an unbranched trunk, making palms unique trees. Fronds come in two forms, pinnate and palmate. Some appear fan-shaped while others appear feather-shaped.
There are many types of palms, and most are easy to grow in well-drained soils and full sunlight. They do not tolerate extended periods of cold. When choosing a palm, be sure that it is hardy to your zone, tolerating temperatures down to 15 to 20 degrees.
Louisianians have several hardy palm trees to choose from. Native palms include cabbage palm, dwarf palmetto, needle palm, saw palmetto and Texas palmetto. Some non-native palms that do well in Louisiana are the Chinese fan palm, Chinese windmill palm, lady palm, Mediterranean fan palm and queen palm.
Palm tree availability may be limited in some areas. Work with local nurseries to explore the species they carry. Additionally, palms can be expensive, especially for larger specimens. Larger trees can be purchased as balled-and-burlapped, requiring equipment to move them. And some are available in containers, making them easier for homeowners.
Palm trees have fibrous root systems that are not deeply rooted but are widely spread like a mat that grows in the top 12 to 36 inches of soil. The root systems can be very extensive. Maintenance on palms is minimal. You should remove any hanging, dead or unhealthy fronds. If you have larger specimens that require a ladder to remove fronds, call a licensed arborist.
Palms can be a great addition to your landscape. Unfortunately, some relatively new diseases affect palms, and I have witnessed more and more cases in East Baton Rouge and the surrounding parishes in the past few years. Two of the diseases are lethal as their names indicate — lethal bronzing and lethal yellowing.
According to Raj Singh, plant doctor and director of the LSU AgCenter Plant Diagnostic Center, the diseases began to appear in 2013 in both Jefferson and St. Bernard parishes. The diseases have continued to spread, reaching East Baton Rouge, Iberia and West Baton Rouge parishes.
The diseases are caused by a phytoplasma, Candidatus palmae. What is a phytoplasm, you might ask? It is a bacterial parasite that attacks the plant phloem tissue (tissue in plants that carries sugars down from the leaves), and sap-sucking insects transmit it.
Phytoplasmas were not discovered until 1967, so scientific knowledge on these pathogens is still growing. The phytoplasma strain that causes lethal bronzing is closely related to the strain that causes lethal yellowing.
The diseases were first observed in Texas and Florida and have now spread to Louisiana and throughout the Gulf States. The symptoms start with discoloration on the tips of the oldest fronds. The fronds then begin to turn bronze and eventually become dead brown, and all the fronds eventually die. This all happens quickly in a matter of weeks.
Lethal yellowing causes decline in 37 palm species, including Chinese fan palm, Chinese windmill palm, date palm, queen palm, silver date palm and Canary Island date palm, all of which can grow in warmer climates in Louisiana.
The disease starts with discoloration of older fronds that eventually leads to death of flowers in addition to premature fruit drop. The center spear frond eventually dies after the trees loses one-third of the lower canopy. The entire tree rapidly dies within three to five months after the appearance of the first symptoms.
The real bad news? Both diseases are terminal and cannot be treated. Palms that test positive must be removed immediately to prevent transmission to healthy plants. Any healthy palms in the area must also be tested.
Have you noticed a sudden change in your palms? Seen a palm just die within a matter of weeks? Samples of the suspected palms can be submitted for testing to the LSU AgCenter Plant Diagnostic Center. Before submitting samples, contact the center by phone at 225-578-4562.
Dwarf saw palmetto is a wonderful native palm that can be used in sustainable landscapes. Photo by Heather Kirk-Ballard/LSU AgCenter
Two photos of the same windmill palm on the LSU campus in Baton Rouge. The photo on the left shows the results of lethal bronzing disease. Left photo by Heather Kirk-Ballard/LSU AgCenter; right photo is an LSU AgCenter file photo by Allen Owings