Lethal Yellowing of Coconut Palms Arrives in San Pedro

(By Dr. Roger Ashburner - Centro de Investigacion Cientifica de Yucatan, Mexico - and Lizandro Quiroz - Ministry of Agriculture and Fisheries.)

It is now apparent that lethal yellowing of coconut palms is present in San Pedro. This is grave news for the community since it threatens to kill the majority of the coconuts on the caye, leaving bare trunks and depleted tourist dollars in its wake. Coconut palms are symbolic of tropical island paradise and foreign visitors expect them to be present when they arrive in the tropics. The image of paradise is now at risk in San Pedro due to the arrival of lethal yellowing disease from the mainland. To prevent the loss of San Pedro's coconut palms and its attractiveness to tourists, community action is now required.

Many of the readers may be familiar with the effect that lethal yellowing is having on the mainland coconuts, particularly in Corozal, Belize and Stann Creek Districts. Lethal yellowing of coconut palms was first detected in northern Belize in 1992. Since then, it has destroyed more than 95% of the tall coconut palms in Corozal, has moved to Orange Walk and has caused serious losses in the Belize District. Since its detection in Stann Creek a year ago, it has infected a great portion of the susceptible palms in Dangriga Town and its outskirts. It is estimated that around 50% of the tall coconut palms in Belize have been infected by the lethal yellowing and its spread is considered rapid.

Lethal yellowing is a fatal disease of coconut and other palms that has killed millions of palms in the Caribbean region over the past 40 years. The disease has swept through the coconut growing regions of Jamaica, Cuba, the Cayman Islands and Florida, and is presently destroying palms in the Yucatan Peninsula, Honduras as well as mainland Belize.

The disease is caused by a small virus-like organism called a phytoplasma and is spread by small plant-sucking insects known as plant-hoppers. There is no effective cure for the disease and, the palm will die within 3 to 6 months after the appearance of the first symptom. The first visible sign that a coconut has been infected is the dropping of all of its fruit, irrespective of their size. Over the next two months or so, the new flowers produced by the palm wither and blacken. Then the leaves progressively yellow and hang, starting from the lower leaves and finishing with the top leaves. Once the top leaves have gone, the palm is dead and all which is left is something resembling a telephone pole.

The disease occurs in discrete areas known as foci. These foci slowly grow larger, gradually taking in more palms. Once lethal yellowing becomes established in an area, most of the coconut palms will die within the next 3 years. The disease may also jump over several kilometers to establish new foci.

Even though there is no cure for lethal yellowing, the disease can be controlled. Short-term control can be effected by injecting the coconut palms with the antibiotic, oxytetracycline. This control method prevents the death of the palm in the short term but is also quite expensive. A more long-term and cheaper solution to the problem is to plant resistant coconut varieties and palm species. It is recommended to use the two control methods in conjunction to keep the old coconut palms alive until the new resistant ones have grown up sufficiently.

Oxytetracycline can be used to prevent coconut palms from catching the disease, but is more often used to keep them alive once they have acquired it. To do this, oxytetracycline has to be injected into the trunk approximately every three months, costing around BZ $60 - $70 per palm per year. For details of how this can be done and where to obtain the necessary equipment and oxytetracycline, contact the Belize National Plant Protection Service at Central Farm (092-2131). This is a short-term solution only.

Resistant coconut and other palm species are the only long-term solution to lethal yellowing. For the replanting of coconut palms, two varieties are currently recommended: Malayan Dwarfs and Maypan (or Mapan) hybrids. There are already Malayan Dwarf palms growing in San Pedro. They can easily be recognized by their short stature and their fruit's yellow or golden colour. Seeds taken from these palms should breed true-to-type and can be used for replanting purposes. However, the Dwarf palms grow very slowly and won't form tall graceful stands of coconuts for some 40 years.

The alternative is to plant the faster-growing Maypan Hybrids. This variety is produced in special seed-gardens by crossing the resistant Malayan Dwarf variety with the medium-resistant Panama Tall variety. Since these hybrids are special crosses, they can only be bought from limited suppliers and are relatively expensive. Recently quoted prices range between BZ $2 and BZ $5 per ungerminated seeds and more for seedlings and established palms. These hybrids are presently available from SACRAC S.A., Apartado 229, Centro Coion, 1007 San Jose, Costa Rica, telephone + 506 2552121 and fax +506 2551348; and from Coconut Industry Board, P.O. Box 204, Kingston 10, Jamaica, telephone +809 9261770 and fax +809 9681360. As from March 1997, these same hybrids will be available from Central Farm.

Some other palm species are susceptible to the disease, the more common ones being, Canary Islands Date Palm, Date Palm, Fiji Fan Palm, Thurston Palm, Windmill Palm, Manila Palm, Footstool Palm, Cabada Palm and Latan Palm. However, still other palm species have been shown to be resistant to lethal yellowing, including all the native palms of the Yucatan Peninsula, such as the Royal Palm, those native to Belize such as the Cohune Palm and still others such as the African Oil Palm.

As well as lethal yellowing disease, red-ring disease of palms is also present in San Pedro. This diseases is caused by microscopic worms known as nematodes. The symptoms of this disease are very similar to those of lethal yellowing and can only be distinguished by the presence of a red ring in the trunk when the palm is felled. No direct control measures are available for red-ring and no resistance has been found. However, it can be controlled by controlling the insect that spreads it, the American palm weevil.

Control of the palm weevil is made by felling affected palms, cutting them into lengths and burning them completely. This will kill any eggs or larvae of the weevil. Damaging healthy palms with machetes and the like should be avoided as they provide breeding sites for the weevil. Trapping systems should also be used to lower the numbers of weevils in the area. These basically contain an attractant, either chemical or fruit such as papaya or pineapple, and an insecticide such as malathion. Details of how to construct these traps can be obtained from Central Farm.

A co-ordinated effort is required in all of these measures in order for the campaign to be successful. Therefore, it is now time to organize community action to save the coconut palms of San Pedro.

For more information on lethal yellowing and how it can be controlled, call the Belize National Plant Protection Service at Central Farm on 092-2131.

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