Ganoderma, a Deadly Disease of Palms

No plant is as closely associated with Florida as a palm tree – the native sabal palmetto is the state tree, in fact! While this and several other species of palm are hardy even into the cooler regions of the panhandle, there are occasionally problems that arise with them. Palms tend to be sturdy in the wind, handle salt spray, and deal with drought without much issue. A few diseases can strike them, however, and the fungal pathogen Ganoderma zonatum is one of them.

Symptoms of a tree infected with Ganoderma butt rot. Image credit: M.L. Elliott

Ganoderma butt rot, caused by this pathogen, can affect any palm tree no matter the species. It only attacks palms, so nearby hardwoods or conifers are safe from it. As a fungal disease, it spreads by spores, which are produced on a conk (a type of mushroom that is wide and flat, usually growing on decaying wood). By the time the conk is visible on the trunk of a palm, the damage is done. The fungus slowly rots away the lower four to five feet of the trunk, working invisibly until it is ready to reproduce.  The trunk of the palm will not become soft or spongy as the disease develops. There may be other outward symptoms of the disease, including slower growth, off-color foliage, and wilting and dying of fronds starting from the older bottom fronds. These symptoms occur with other diseases and problems as well, making it difficult to diagnose Ganoderma butt rot until the conk is visible.

A conk will start out as a small, white, button-like growth on the trunk. As it grows, it expands, flattens out, and develops a brown or reddish-brown coating on top. Old conks turn fully brown. It is uncertain how long it takes a newly infected palm to develop conks; it may be months or even years.

Once a tree is infected with this fungus, there is no cure. Removal of the tree is the only option, and as much of the trunk, stump, and roots as possible should be taken out. Conks may form on stumps after the palm is cut down, which can help to spread the disease. The fungus, unfortunately, persists in the soil even after the palm is removed, so infected palms should be replaced with other types of plants.

A small, relatively newly formed conk.

Frustratingly, the disease is difficult to predict. There do not seem to be any conditions that favor the disease in particular – it has been observed on otherwise healthy plants as well as stressed ones, and on naturally growing palms as well as those that have been transplanted. Still, keeping plants of any sort as healthy as possible can help them to resist pests and diseases, so fertilize, irrigate, and prune palms properly.

Evan Anderson

Walton County Horticulture Agent