Rotten Falling Palms

Hygiene, hygiene, hygiene - but only after palms die. If you have unexplained falling, rotting palms, then one of these two diseases may be involved.

They occur in the NT, as well as many tropical regions around the world.

Ganoderma Butt Rot of Palms
· Ganoderma butt rot is caused by the fungus Ganoderma zonatum. This fungus degrades or rots the lower 1-1.5m of the trunk.
· All palms are considered hosts of this fungus. This fungus is not a primary pathogen of any other plant species.
· Symptoms may include wilting (mild to severe) or a general decline.

The disease is confirmed by observing the basidiocarp (conk) on the trunk. This is a hard, shelf-like structure that will be attached to the lower 1 - 1.5m of the palm trunk. However, not all diseased palms produce conks prior to death.
· A palm cannot be diagnosed with Ganoderma butt rot until the basidiocarp (conk) forms on the trunk, or the internal rotting of the trunk is observed after the palm is cut down.
· The fungus is spread by spores, which are produced and released from the basidiocarp (conk) [seen upside down in the left photo].
· Conditions that are conducive for disease development are unknown.
· There are currently no cultural or chemical controls for preventing the disease or for curing the disease once the palm is infected.
· A palm should be removed as soon as possible after the conks appear on the trunk. Remove as much of the stump and root system as possible when the palm is removed.
· Because the fungus survives in the soil, do not plant another palm back in that same location.

Thielaviopsis Trunk Rot of Palm
· Thielaviopsis trunk rot is caused by the fungus Thielaviopsis paradoxa.
· Due to this disease, the palm trunk either collapses on itself or the canopy suddenly falls off the trunk, both without warning. The palm canopy often appears healthy prior to collapse.
· Except for “stem bleeding,” which is common in coconut and some single stem palms, there may be no symptoms prior to collapse of the palm.
· Only fresh trunk wounds will become infected by the fungus, so disease management includes limiting man-made wounds to the palm trunk, especially the upper third of the trunk.
· If the disease is detected early, cutting out the rotted, infested wood followed by spraying the wound site with a fungicide may be useful.
· There are no other methods to prevent or cure this disease. The palm should be removed immediately, and the diseased trunk portion destroyed but not recycled.

Thielaviopsis paradoxa is a fungus that can infect any part of a palm, and so can cause numerous diseases. In Florida, the two most frequent (and usually lethal) Thielaviopsis diseases observed in the landscape and field nursery are a bud (heart) rot and trunk rot.

Unfortunately, there often are no visible indications that a palm has Thielaviopsis trunk rot until either the trunk collapses on itself or the canopy suddenly falls off the trunk. The canopy often appears normal and healthy.

Thus, there are no symptoms that can be used to predict which palms are infected and which ones are not. In most cases, the trunk rot is occurring in the upper half of the trunk. This may occur because the number of lignified fibers are greatest in the lower trunk and least in the upper trunk. As indicated previously, this fungus prefers to rot non-lignified or lightly lignified plant tissue. “Stem bleeding” is a common symptom of Thielaviopsis trunk rot observed on single stem palms eg coconut, royal palms. This stem bleeding is a reddish-brown stain that runs down the trunk from the point of infection.

Thielaviopsis trunk rot usually occurs quite randomly, with only a few palms in the landscape being affected. However, there are situations where high numbers of palms in a single landscape can become diseased, for reasons that are not always clear. In all situations, there has to be a fresh wound to the palm. Wounds can occur naturally, such as trunk cracks due to excess water uptake. Insects (such as beetles), birds (sapsuckers pounding on the trunk), rats, and other mammals can cause wounds. Blowing objects during a wind storm can strike a trunk and cause a fresh wound.

Humans cause wounds with nails and climbing spikes, or during the digging and transplanting process.

Humans also create wounds when trimming leaves that are not yet dead. Leaf petioles are cut as close as possible to the trunk. If a leaf petiole has any green color associated with it, the leaf is still living. When that still living petiole is cut, a fresh wound is created that may be infected by the fungus. Trunks can be easily wounded during the trimming process with the careless use of the pruning tool. Pulling a leaf off the trunk, when the leaf petiole still has green tissue, can create a fresh wound.

The fungal pathogen can spread from palm to palm as follows. First, if spores are produced on diseased palm tissue, these spores can be moved by wind and water to fresh wounds. The spores may also be moved about by insects or rodents. Second, the spores that can survive in the environment, especially soil, for long periods. Fresh wounds could become infected via contaminated soil.

Except for the stem bleeding, there are often no outwardly visible symptoms that indicate which palm in the landscape or field nursery has Thielaviopsis trunk rot. Thus, there are no proven strategies for preventing this disease. Once the palm has collapsed, remove it immediately as it is a source of fungal spores.

If one does observe the initial stages of the trunk rot, such as the stem bleeding, it would be useful to cut out the area of rotted wood (if it is not too large a trunk area) and spray the wound thoroughly with a fungicide labeled for Thielaviopsis diseases. Examples include, but are not limited to, products with the active ingredients thiophanate methyl or fludioxonil. The goal is to prevent the fungus from infecting the fresh wound made when you cut out the infested, rotted wood. All tools used to remove the rotted wood must be cleaned with a disinfectant. [Banrot is a possible trade name]

Examples of disinfectants include: 1) 25% chlorine bleach (3 parts water and 1 part bleach); 2) 25% pine oil cleaner (3 parts water and 1 part pine oil cleaner); 3) 50% rubbing alcohol (70% isopropyl; equal parts alcohol and water); 4) 50% denatured ethanol (95%; equal parts alcohol and water); 5) 5% quatenary ammonium salts. Soak tools for 10 minutes and rinse in clean water. For chain saws, soak chain and bar separately.

Diseased trunk material should be destroyed and should not be recycled in the landscape. Chipping and then spreading the infested material in the landscape could spread the fungus to healthy palms. If the trunk is chipped, it should be placed in a properly constructed and monitored compost heap, or taken to a landfill or incinerator.

[partially sourced from extension articles - Monica Elliott et al, Uni of Florida; all photos from Darwin]