Sally Scalera

Brevard County Horticulture Extension Agent
3695 Lake Drive -- Cocoa FL 32926 -- 321-633-1702

Palm diseases

Aug. 16, 2008

If you have palms planted in your landscape you may want to pay attention to this article. We have a few new diseases that hit palms and one that has been around for a long time, Ganoderma butt rot.

For some background, all palms, as well as cycads, are susceptible to Ganoderma butt rot which is a fatal disease with no known cure. It is easily spread by wind blown spores, dirty shovels containing contaminated soil, etc. The fungal genus Ganoderma is a group of wood-decaying fungi that are found throughout the world on all types of wood including conifers, hardwood & softwood trees and palms. There are many different species of this fungus, but only one is a pathogen of palms in Florida. That fungus is Ganoderma zonatum. The conk is the most easily identifiable structure associated with the fungus. When the conk first starts to form on the side of a palm trunk or stump, it is a solid white mass that is relatively soft when touched. The “white button” is the beginning stage of the conk. As the conk matures, a small shelf or bracket will start to. Eventually, it will form a very distinct shelf-like structure that is quite hard with a reddish-brown top surface and a white underside. A mature conk will have distinct zones, hence the name G. zonatum.

Once a palm is infected with G. zonatum, the fungus will move with that palm to the location in which it is transplanted. The primary symptom that may be observed is a wilting, mild to severe, of all leaves but the spear leaf. Other symptoms can best be described as a general decline, slower growth and off-color foliage. However, these symptoms alone should not be used for diagnosis of Ganoderma butt rot, since other disorders or diseases may also cause these symptoms. Only when these symptoms are accompanied by the development of the conk can the palm be diagnosed with Ganoderma butt rot. Also, it has been observed that conks can form prior to any obvious wilting or decline symptoms. The opposite is also true where the palm could show decline before the conk appears.

In general, the fungus will be located in the lower five feet of the trunk. This has three implications. First, this means that the fungus is not spread with pruning tools since the fungus is not associated with leaves. Second, this means that only the lower trunk portion should NOT be chipped and used for mulch. Third, there are no fungicides that can systemically protect the palm either during, before or after infection. Once you observe a conk on a palm, the palm should be removed immediately for safety reasons. These palms are likely to be the first blown down in heavy winds. Because the fungus survives in the soil do not plant another palm in the same spot where a palm has died from Ganoderma butt rot. If your palm dies and all of the fronds are hanging down around the trunk then cut it down but leave a stump so that you can check for the appearance of conks.

A relatively new disease that has shown up is just hitting Queen palms and Mexican fan palms. The symptoms are the opposite of Ganoderma in that the lower or oldest three fronds will turn brown and then the next three will go brown until the entire canopy is brown but still held upright. This disease moves rapidly and the entire canopy can turn brown in a couple of months. The pathogen is Fusarium oxysporum and is called Fusarium decline. Once again, there is no cure for this disease and the recommendation is to not replant with a queen palm or Mexican fan palm.

The newest palm disease came to light recently due to reports of substantial numbers of Sabal palmetto (cabbage palm or sabal palm) dying in Manatee and Hillsborough Counties. Observations of symptomatic palms in Manatee County, followed by removal and analysis of trunk corings have confirmed that a phytoplasma is consistently present in these affected in palms. The preliminary analysis indicates that the phytoplasma that causes Texas Phoenix palm decline is also causing the decline of the cabbage palms. See http://edis.ifas.ufl.edu/PP163 for more details about this disease. The previously known palm hosts for this particular phytoplasma are Phoenix canariensis, Phoenix dactylifera, Phoenix sylvestris and Syagrus romanzoffiana. Unfortunately, we can now add Sabal palmetto to this list.