Until recently, Hawaii's palm trees have had relatively few serious pest and disease problems. Unlike Florida and the Caribbean, Hawaii was spared the ravages of deadly yellowing disease, which killed most coconut palms in the region during the 20th century.
The key to avoiding the deadly yellows disease here was to have strict regulations and penalties on the importation of palms from affected areas. With inspection of imported plants by the Hawaii Department of Agriculture and the USDA, plus assistance from the University of Hawaii Tropical Studies and Hawaii Landscaping Industries, we have avoided many other diseases and pests.
Unfortunately, we are now threatened by a new problem that could devastate our environment: the coconut longhorn beetle, which could kill not only coconut palms but many other species as well, including the very rare endemic Pritchardian palm that evolved here.
This large horny beetle is found on the Big Island of Hawaii and can easily be spread by humans. For example, green waste containing larvae and adults is often composted and used as mulch by local gardeners. At this point, we should carefully inspect the mulch, compost, and palm trees we transport. This beetle also damages sugarcane and pandanus or hara plants. The beetle measures about 2 inches. The larvae can grow up to 4 inches before pupating. They first attack palm buds, which emerge with the new leaves wounded. If you think you have found an infested palm, beetles, or larvae, please visit crbhawaii.org to report the sighting and get more information.
Why is this so important? When we think of the tropics, the first trees that come to mind are the coconut palms that adorn the white coral sand beaches. In fact, these palms have been transported by humans throughout the tropical world for thousands of years. Taxonomists, botanists, and anthropologists have tried to figure out the origins of this precious tree, but no one is sure. One theory is that the species evolved in the Australian region hundreds of thousands of years ago, as some of the oldest records suggest. It may have even evolved when the interior of Australia was an ocean.
Either way, coconut palms are one of our favorite trees for scenery, food, and shelter. There are hundreds of palm species around the world, most of which live in tropical and subtropical regions. Some grow in desert environments, others in moist rainforest areas. But some are found in cold mountainous regions like the Andes and Himalayas. Some of these may even grow as far north as Seattle, Washington.
Hawaii's gardens are home to hundreds of rare palm species. There are hundreds of palm species around the world, with new discoveries every year. They range from high mountain species like the Andean wax palm, which lives 13,000 feet above sea level, to equatorial rainforests like the Amazon. There are also desert palms, a large group, but none are as familiar to Hawaiians as the coconut palm. The coconut palm group has numerous varieties, including dwarf species that should be used more in Hawaii. Not only are they short and easy to harvest, but they are also resistant to the devastating lethal yellowing disease.
Palm trees here have historically been relatively free from serious pests and diseases. Hawaiian palms can suffer from bud rot and trunk bleeding disease, caused by physical damage from unsanitary pruning equipment or vines. Most of the palms that are yellowing or stunted are found to be lacking in fertilizer and water. All of these problems are fixable, but if the deadly yellowing were to reach Hawaii or if the coconut beetle were to become infested, there would be no realistic way to stop the destruction of the islands' palm trees.
When the deadly yellows disease hit mainland Florida, many other palm species were found to be susceptible to the disease to varying degrees. Florida embarked on a two-phase program of replanting; over 500,000 dwarf coconuts were imported. Not only were dwarf coconuts highly resistant to the disease, they also had the advantage that their fruit was easily harvested, without the need for costly removal of fruit and leaves as was the case with the taller varieties.
Hawaii is fortunate to be far from disease-hit areas, so it is crucial that we prevent the introduction of this and other plant pests. With regard to the coconut beetle, we need to support research efforts such as biological control and insecticide management to contain this pest. Fortunately, there are several nurseries, such as Sutin and Jeff Marcus' Floribunda, that collect palm seeds from around the world for parks and gardens, but Jeff and Sutin warn that it may be too late to prevent mass losses of palms.
To keep your palm trees free of disease and pests, it’s important to be vigilant and work with the Hawaii State and Federal Departments of Agriculture to follow all inspection regulations.
Norman Bezona is Professor Emeritus in the School of Tropical Agriculture and Human Resources at the University of Hawaii.
