Hawaiian gardens include hundreds of species of rare palms. As far as the U.S. is concerned, even the coconut palm can only be grown here and the southern tip of Florida. When it comes to species of palms in the world, there are thousands with more discovered each year. They come from the high mountains like the Andean wax palms that live at 13,000 feet above sea level to equatorial rainforest species like those from the Amazon.
Desert palms are another large group, but none is quite so close to our Hawaiian hearts as the coconut palm. The coconut palm group is composed of scores of varieties including some dwarf types that should be used more in Hawaii. Not only are they shorter and easy to harvest, they are resistant to a devastating disease referred to as lethal yellowing. Our endemic loulu palms (Pritchardia species) are very prone to this disease.
Palms here have few serious diseases at present. Hawaii’s palms may be affected by bud rot or stem bleeding disease that is often caused by physical damage such as unsanitary pruning equipment or climbing spikes. Most palms showing yellow or stunted growth have been found to be suffering from lack of fertilizer or water. For example, a recent report came from concerned citizens calling about the dead and dying trees around Kona. The trees simply need a balanced fertilizer plus minor elements, applied three to four times per year, and regular irrigation. All these problems are correctable, but if lethal yellowing ever gets in Hawaii, there’s no practical way of stopping destruction of our island’s palms. Not only would the coconut palm be destroyed, but over 100 species of native and exotic palms would also die.
To realize the full potential threat of lethal yellowing, picture the streets of Waikiki and Kahala with tens of thousands of dying coconut palms in all stages of the disease, from the early brassy yellowing of the lower fronds through the collapsing of the crown and the final “telephone poling” when there is nothing more than a naked trunk.
This disease, originally thought to be a disease exclusively of coconut palms, occurs in the West Indies, Florida, Texas, Mexico and Africa. A similar disease occurs in the Philippines.
Lethal yellowing hit Key West, Florida, in the middle 1950s. After a number of years and killing, 3/4 of the coconut palms, it stopped. In the early 1970s, it was found in the greater Miami area. Since the Jamaica tall coconut palms are the one that had been planted almost exclusively in Florida, the disease ran rampant. By 1980, most coconut palms in South Florida were dead.
Research at the Coconut Industry Board in Kingston, Jamaica showed that all varieties of coconuts are susceptible to lethal yellowing. The degree of susceptibility has been the point for developing varieties that are resistant. The dwarf types are least susceptible.
When lethal yellowing hit the mainland of Florida, it was discovered that many other palms were also susceptible to the disease in varying degrees. According to the University of Florida Lethal yellowing Research Station in Fort Lauderdale, hundreds of other palms are susceptible like the manila palm, fishtail palm, loulu palm, date palm, oil palm and many others.
Mycoplasma-like organisms, that occupy a niche between a virus and bacteria, are the cause of lethal yellowing. Mycoplasma-like cells were found in tissues of all diseased palms examined by the University of Florida scientists at the research station in Fort Lauderdale. They appeared to be transmitted by a leafhopper. Remember, neither the disease or leafhopper have been found in Hawaii.
Hawaii is fortunate to be far from disease affected regions, but it is vital that we don’t introduce this and other plant plagues. It is important to cooperate with the Hawaii and Federal Departments of Agriculture and follow all the rules of inspection.