Imagine arriving in Hawaii
and realizing that a majority of coconut trees in the islands have become extinct. That would be akin to discovering that flowers associated with Hawaii – hibiscus and orchids – have disappeared from the landscape of this remote tropical paradise thousands of miles from the Mainland, in the middle of the Pacific Ocean.
An insidious, devastating “cancer” is decimating coconut trees in Hawaii at an alarming rate – 15 percent of the trees have been destroyed by a deadly pathogen known as Phytophthora katsurae, which causes coconut heart rot.
What are the symptoms of Phytophthora?
Abnormal loss of small to nearly mature nuts has been a common early sign of the disease. Infected fruits have dark, mottled spots and rots. Irregular expansion of brown infected areas frequently creates circular green patches or islands of green tissue surrounded by diseased areas. Water soaking is also common on large immature fruits and appears as dark green, oily tissue bordering diseased areas.
Young diseased fruits less than three inches long are generally brown without mottling. Internally, the infected husk of older fruits is reddish to red-brown. The infected meat, or endosperm, is white, cream colored, or slightly brown. The pathogen may penetrate mature nuts by growing through germination pore at the stem end of the nut.
The first symptoms of young or mature trees are wilting, discoloration, and death of the youngest leaf. Unfurled spear leaves may also die early in the course of the disease. Dead fronds are bent abnormally, but remain attached to the trunk for a few weeks, drooping onto or between the older green leaves.
In the ensuing months, more leaves die and fall, leaving a few lower fronds. Roots and lower trunk tissue remain healthy and functional for many months, and continue to supply the lower leaves with nutrients and moisture.
Eventually all of the fronds drop, producing leafless trunks. Less frequently, older leaves die first, resulting in trees with only a few young, upright fronds. Because young leaves are vertically oriented, infected plants appear rigid. By the time leaf death is observed, internal heart rot is already at an advanced stage. These diseased trees have large rotted areas that involve most of the terminal bud.
Killing of the single growing tip ultimately causes the death of the palm. Diseased nuts and heart rots, followed by plant death, have been associated with a Phytophthora species. The pathogen of coconut produces abundant and distinctive sexual spores in host tissue. Each spore is produced in a mother cell that has distinctive blister-like swellings and a long base.
How to Combat the Pathogen
Once trees are infected, death from the disease appears to be inevitable, and several hundred trees have been lost throughout Hawaii since 1970. Because the host range of Phytophthora appears to be confined to coconut, eradication and exclusion are feasible control options. All infected trees and nuts should be destroyed by incineration or deep burial.
Prompt removal of diseased trees will reduce the probability of soil contamination with the pathogen. The sexual spores of most Phytophthora species are able to survive in soil without the host plant. Removal of diseased material will also prevent spread of the pathogen to healthy trees.
Many diseased trees have been observed in wet windward areas of Kauai, the Big Island and Oahu and Maui. Growers should avoid collecting coconut-planting material from these areas. Since mature trees may be infected, yet remain without symptoms for many months, careful selection of clean nuts and healthy seedlings and trees is necessary.
Stock plants or young seedlings should be grown in relatively dry areas to minimize establishment of the pathogen on new plants. Because of the epidemiology of the disease in Hawaii is not known, the exact means by which the pathogen spreads are not specifically known.
Based on studies of other Phytophthora diseases however, wind-driven rain, insect feeding and movement or activities of other small animals are probably important factors in the spread of the disease. Moisture strongly favors the growth, spore production, and spread of the pathogen, and disease development by Phytophthora.
Sexual spores of the pathogen occur in large numbers within diseased husks and trunks. These thick-walled resistant structures allow the pathogen to survive for long periods in a dormant state. The pathogen is seed-borne as sexual spores are common in the husk of the diseased fruits.
The removal of nut clusters and heavy leaf pruning of large trees have probably aided disease spread. Microscopic spores from diseased tissue will contaminate cutting tools and infect healthy trees during subsequent pruning operations. Furthermore, wounding the stem base by cutting off green fronds exposes highly susceptible plant tissue to pathogen infections.
When feasible, tree trimming should be done during dry weather. Tools should be cleaned, then immersed in a disinfectant after trimming operations on each tree are completed, especially at sites known to have the disease.
Fungicides such as Subdue 2E (metalaxyl), Dithane M-45 (mancozeb), Aliette (fosethyl-Al), and Truban (ethazole) are known to be effective protectants against other Phytophthora diseases, but they are ineffective for curing trees with advanced rots of the heart or terminal bud.
Limited control of the disease in the early stages may be attained by removing diseased fruits on trees that don’t have young dead leaves, then protecting the wound surface with a pruning sealant, thus preventing disease progression into the trunk. A good plan is to plant coconut trees more often. The life span of a coconut tree may be only 15 to 25 years with this disease in Hawaii, thus younger trees should be planted periodically.
From Genesis to Epidemic Proportions
Coconut trees had been relatively disease free in Hawaii, prior to the discovery of Phytophthora katsurae in 1971 by Dr. Minoru Aragaki from a specimen collected at Wailua, Kauai, according to the University of Hawaii College of Tropical Agriculture and Human Resources (CTAHR) in Honolulu. Infected trees died within one year. Aragaki and Dr. Janice Uchida worked on the disease over the years.
During the 1980s, Phytophthora was found on Oahu, Maui and the Big Island as well. Interisland movement of nuts, seedlings, and large trees, as well as tree trimming operations, probably contributed to the disease escalating to epidemic proportions.
Fearful that a centuries-old icon in Hawaii could become extinct in the not too distant future, experts here have launched a concerted effort to combat coconut heart rot. Philippe Visintainer, owner operator of Hawaii Coconut Protectors on Maui, is leading the battle against Phytophthora with unabashed zeal.
“The University of Hawaii started research on Kauai in the late 80s,” Visintainer says. “Hurricane Iniki hit Kauai in 1992 and destroyed the research plot. Nothing was done to control the disease in the environment until I took over the project in the late 90s. I was managing a tropical plantation on Maui. I planted lots of coconut trees on properties, and I noticed that some of the trees were dying. I was concerned about it, so I talked to the University of Hawaii, the Department of Agriculture and other pathogen specialists.”
Visintainer invited experts from around the world to Maui to assist in establishing research plots. They experimented with different formulas to combat the pathogen. Visintainer has been on the board of directors of the Maui Farm Bureau for about six years.
As part of the board of directors, he advocated a bill in the Hawaii State Legislature in 2000, to extend research on coconut heart rot. The bill was passed and $10,000 was appropriated for the project. Visintainer realized that research on Phytophthora would be stymied, if he didn’t wage an all-out war against the pathogen.
Making a Commitment
“I stopped working at the plantation and started a company called Hawaii Coconut Protectors,” Visintainer says. “We’ve been airing a video on public television on all the islands, outlining the spread of coconut heart rot and what we are doing to combat it. Our approach was to educate the public about the pathogen. We met with people in the landscape industry in conjunction with the University of Hawaii. We conducted research. We offered an injection program statewide that protects coconut trees from the pathogen. Other than that, we’re promoting eradication. In the next few years, we want to implement an eradication program through a federal government grant. We haven’t applied for a grant yet, because it’s not a good time to be asking for money.”
The injection formula has been successful, according to Visintainer. He has been working with hotels, resorts, condos and private owners in Hawaii. Visintainer is also trying to get Maui county to take action against the pathogen. His company developed a formula based on phosphorous acid.
Visintainer refers to it as the nutrient augmentation approach. The injection promotes the general health of a coconut tree, and fertilizes it. At the same time, it creates an environment in the heart of the palm that repels the pathogen.
“We inject trees at about chest high, and the formula is systemic, so the tree will carry the formula to the top of the leaves and back down into the heart of the palm in about two to four weeks, depending on the tree,” Visintainer says. “We’ve achieved a 95 percent success rate with healthy trees. We’re not certain how the pathogen spreads, whether it’s by way of rodents, tree trimming, or insects. It appears that wind-driven rain is a major factor. It moves around with the wind and rain, and gets into the crown of the tree, and works its way into the heart of the palm.”
Visintainer usually saves five to 15 percent of infected trees. Most of the time, by the time he examines the trees, and people have realized that they have a problem, the trees are rotten. There’s nothing Visintainer can do at that point. There are 350 species of the pathogen worldwide, and it has invaded numerous different plants, ranging from pineapples to oak trees.
Visintainer speculates that the pathogen arrived in Hawaii when travelers brought plants and materials here. At this point, the pathogen is unique only to coconut trees in Hawaii. It started on the windward side of the islands, but has spread to the leeward side of the islands. Visintainer has identified infestations at golf courses. He reasons that maintenance crews provide volumes of water to keep courses green, so coconut trees receive volumes of water too.
Educating the Public
“This encourages the spread of the pathogen, because it thrives on moisture,” Visintainer says. “In Hawaii, we have high levels of moisture and humidity. People would care about the pathogen, if they were aware of it. We’re talking about probably tens of thousands of coconut trees. If you have a tree dying from the pathogen, it’s only one tree out of perhaps a grove of 50 trees, so it’s often difficult to recognize the pathogen and its potential to infect more trees. By the time the tree is sick and dead, tree trimmers may come along and cut the tree down. There are still 49 coconut trees, so it doesn’t appear that there’s a serious problem. However, you don’t wait until 30 percent of the population is infected with AIDS, to recognize the problem. By then, you’ve lost the battle.”
With the coconut trees, experts have an opportunity to manage the pathogen before it’s beyond control, according to Visintainer. He has received support from many people. “We charge a fee for injections, which is $20 per coconut tree, and if there are 50 trees or more, we charge $15 per tree,” Visintainer says. “There is much more awareness today than there was five to 10 years ago. There’s a good possibility that we’ll win the battle.”
A Word from the Research Community
Dr. Jeri Ooka, plant pathologist, Department of Plant and Environmental Protection Sciences, College of Tropical Agriculture and Human Resources (CTAHR), University of Hawaii at Kauai, began working on the disease during the 1982 through 1985 epidemic and recognized the fruit rot phase of the disease.
Ooka demonstrated pathogenicity with isolates of the pathogen. During the mid 1980s, Drs. Aragaki, Uchida, Norman Nagata and others in Uchida’s group confirmed pathogenicity of Phytophthora katsurae on fruits and young plants. These experiments were the first that identified the causal agent, as pure cultures of the pathogen were placed on healthy hosts, which became diseased.
Molokai has not been surveyed well, but it appears to be free of the disease on the leeward side of the island, according to Ooka. It’s certain that bud rot caused by pathogen was here in 1971. It’s probable that the disease was here in 1966. Moving trees around during the last 30 years has spread the pathogen faster than it would have spread naturally. The value of the trees has made the disease more noticeable. Each tree is worth more than $1,000 and the trees are extremely difficult to replace.
“From 1982 through 1992 several field trials were implemented to test various fungicides for control of the disease,” Ooka says. “Early trials involved placing copper-based fungicides in the leaf whorl of the tree. Later trials were generally with different rates of the systemic fungicides metalaxyl and fosethyl-Al as sprays, drenches or injections. Potassium phosphite was the last compound to be added to trials. The last formal trial I conducted was in 1992. This trial was abruptly terminated by Hurricane Iniki. All trials were inconclusive with fosethyl-Al and potassium phosphite showing the best promise and metalaxyl the least.”
The formula to inject coconut trees was derived from South African, American, European and Australian publications reporting use of metalaxyl, fosethyl-Al, injectable fosethyl-Al and potassium phosphite for control of diseases caused by Phytophthora, according to Ooka. The disease is known to landscapers familiar with coconut trees.
Tree trimmers almost always know of the disease, but not necessarily its details. Homeowners, condominium association boards of directors, hotel grounds keepers, and golf courses greens keepers become aware of the disease as it affects their trees. Ooka notes that bud rot will never eliminate all coconuts in Hawaii.
Ooka explains that Hawaii is a dynamic biological system with many factors affecting the balance between pathogen and host, which results in the presence or absence of disease. There are biological, economic, cultural, and aesthetic reasons to preserve coconut trees. Cocos nucifera is the only remaining species in its genus.
It’s a traditional economic plant for the low land tropics, which provides many of the raw materials for survival in oceanic or tropical subsistence systems. For industrial economies, coconut oil was at one time an important raw material for manufacturing products. It has gained cultural importance in societies that depend on it.
“It’s an important ornamental, which identifies Hawaii and other such places as a tropical paradise to tourists,” Ooka says. “The pathogen will never be completely eradicated. In that sense, we can’t win a war against it. As the host changes, so do pathogens. Sometimes the environment is allied with the host, other times with the pathogen. Our objective is to keep disease severity and occurrence at an economically tolerable level.”
Application of the principals of public health goes a long way towards doing this, according to Ooka. There are things that people can do to prevent the pathogen from spreading, such as starting plants from clean seed, collected from healthy trees grown in a dry environment.
Ooka recommends germinating the seed in a good container mix, amended with disease suppressive compost. Once they’re planted in the field, plants shouldn’t be excessively fertilized watered. Trees from wet, cool areas that have a higher likelihood of being infected, shouldn’t be used for transplanting.
“Don’t plant trees in inappropriate sites,” Ooka says. “For example, don’t plant trees in an environment suitable for disease and unsuitable for coconuts. This would include most sites more than 1,000 feet high, or with more than 100 inches of rain yearly, on the windward side of the island. If you plant in such areas, the tree will survive no more than 20 years. In endemic bud rot areas, trees will probably succumb to the disease in 10 to 15 years. In dry areas suitable for coconuts, nitrogen fertilizer and watering should be monitored to avoid creating too many tissues susceptible to the pathogen.”
If Visintainer, other experts, and the community in Hawaii can successfully wage a war against Phytophthora – and win – then their commitment to protect and preserve coconut trees in the islands will be worthwhile. The arduous process of educating the public about the disease, as well as raising the level of awareness and concern, is a good start. Meanwhile, another coconut tree dies with each passing day – leaving one less symbol of Hawaii for future generations.