Ornamental palms vulnerable to disease

Considered the princes of the plant world, palms are unlike many plant families in the fact that they provide both food and shelter to people, while at the same time are admired and collected for aesthetic reasons. But according to plant pathologists with The American Phytopathological Society (APS), the same genetic structure that gives the palm so many wonderful attributes is the same structure that makes them susceptible to lethal and destructive diseases.

According to Monica Elliott, plant pathology professor at the University of Florida’s Fort Lauderdale Research and Education Center, the palm’s anatomy is more similar to that of a corn plant than that of an oak tree, with each stem having a single bud or heart. Once that tissue is damaged, death is likely. “Palms cannot repair injuries to their stems, and diligent effort must be made to prevent injuries that create opportunities for insect or pathogen invasion of the trunk,” she said.

Ganoderma butt rot and Phytophthora bud rot are just two of the most problematic diseases of palms. Ganoderma butt rot, caused by the fungus Ganoderma zonatum, is prevalent in Florida, where it has been found on more than 50 palm species. “Ganoderma butt rot is always a lethal disease of palms,” said Elliott. “By the time symptoms develop, usually more than half of the lower trunk has been killed by the fungus,” she said. In Florida, palm trees of 58 species have died from this fungus and no effective controls are known for this disease.

Phytophthora bud rot can be caused by several species of Phytophthora, and occurs in most places where palms are grown. This pathogen has been reported on palms from more than 20 countries as well as from California, Florida, Hawaii, and Puerto Rico. In total, the species of Phytophthora have a broad host range and have been reported to attack more than 25 palm species. “Bud rot is always fatal to coconut trees, but other smaller palms like parlor palms have been saved by application of metalaxyl to prevent pathogen establishment,” said Janice Uchida, plant pathologist from the University of Hawaii. Uchida’s laboratory is currently screening new chemicals to control Phytophthora diseases.

More on this subject, including factors leading to infection, symptoms, and disease management strategies, is available in The Compendium of Ornamental Palm Diseases and Disorders published by APS PRESS (http://www.shopapspress.org/newandonsath1.html). Additional information on palm disease can also be found in this month’s APS feature article at http://www.apsnet.org/online/feature/palm.

The American Phytopathological Society (APS) is a non-profit, professional scientific organization leading the fight against plant diseases for a healthier world with 5,000 members worldwide.