Fusarium Wilt on Palm Trees

Fusarium Wilt

• Fusarium wilt is caused by forms of Fusarium oxysporum, a fungus that grows inside the xylem of palm trees. Xylem tissue consists of tubes that water flows through within the trunk, stems and leaf veins of palm trees. The fungus plugs up the tubes, resulting in wilting and eventual death of plant tissues. The disease is spread by contaminated pruning tools, transfer of infected soil where infected trees have grown, and perhaps by seeds from infected trees. The form of Fusarium oxysporum most common as a pathogen in the United States is f. species canariensis, first detected in California in the 1970s. It has also been found in Florida, Australia, Japan, Italy, Greece and France. It attacks primarily Canary Island date palms, although other palms are also susceptible.

Palms Infected by Fusarium

• Besides Canary Island date palm, Fusarium oxysporum f. sp. canariensis attacks date palms, Senegal date palms, wild date palms and California fan palms. Another strain of Fusarium wilt, Fusarium oxysporum f. sp. albedinis, is called Bayoud disease and infects only date palms--or Phoenix dactylifera--in Algeria and Morocco. In Central Africa and South America, oil palms of the genus Elaeis succumb to Fusarium wilt of oil palm, Fusarium oxysporum f. sp. elaeidis.

Symptoms

• Palm trees can have Fusarium wilt for months before they display symptoms. Palms have leaves attached directly to the crown of the tree by a stem or petiole, and leaflets, called pinnae, attach to the stem's sides to make the entire palm frond. A characteristic sign of Fusarium infection is one-sided wilt, where the leaflets on just one side of the frond wilt and die from the bottom up. A dark brown streak appears on the stem of the affected side. Fronds nearest the trunk usually die first. When the stem is cut open, the xylem vessels show a brown discoloration.

Diagnosis

• There are other diseases with similar symptoms. Two other fungi, Dothiorella and Gliolcadium, can cause one-sided wilt and xylem discoloration. To diagnose Fusarium wilt, tissue from diseased palms is taken to a laboratory for culture. The isolated disease organism is then subjected to molecular diagnosis. If Fusarium oxysporum f. sp. canariensis is identified, stringent control measures need to be taken.

Treatment

• Remove the infected tree to prevent further spread of Fusarium wilt. Dig out as much of the root system as possible. Incinerate the tree or remove it to a landfill. All equipment used--saws, gloves, shovels, heavy equipment--needs to be cleaned and disinfected immediately. Chain saws should be disassembled for thorough soaking in disinfectant. For maintenance pruning of established trees, prune any palm species that could be a potential host to Fusarium wilt with tools that are cleaned and disinfected between each tree pruned. Keep pruning to a minimum, especially for Canary Island palms. Don't plant susceptible palms back in an area where an infected tree has been removed because the fungus spores remain in the soil for a long time. Don't reuse or relocate infected soil. Seeds from infected trees should not be germinated because of possible contamination by spores. These seem like heroic measures, but palm trees are valuable commodities. It can cost over $10,000 to replace a large Canary Island date palm.