Lethal Yellowing

A tropical paradise is not complete unless you have swaying palm trees, right? Right!

Our island has thousands of coconut palms and, at one time in the past, coconuts were an export product that was sent to the U.S. from the island along with bananas and, I believe, pineapples.

Over the years the exportation of coconuts, pineapples and bananas from Guanaja has ceased when it was taken over by the big companies on the Mainland. We still have coconut palms but over the past few years we have become victims of Lethal Yellowing. Due to this disease, which seems to have no cure, the island has lost at least 45-50% of its coconut trees.

Lethal yellowing is a disease first noticed in the Caribbean region of North America about 100 years ago. However, it was not until the 1950s and a devastating outbreak in Jamaica and the Florida Keys that the economic consequences of lethal yellowing were recognized and intensive research begun. More recently, the disease has spread to other areas of Florida and into Texas. There is no cure for lethal yellowing although it can be controlled in valuable trees with regular injections (four times annually) of oxytetracycline.

While there is not, as yet definitive proof, the lethal yellowing micro-organism is most likely spread by an insect, the planthopper (myndus crudus). Again, research is continuing into the way in which this insect spreads the disease. Tests have demonstrated that insecticides can slow the spread of planthoppers and, with them, lethal yellowing. However, large-scale spraying using currently available chemicals is ecologically damaging and not economically viable. Another approach may be to develop a groundcover that discourages the insect, as young planthoppers feed on common grasses, but there have been no concrete results so far. I did read somewhere, however, that it is best to keep the ground cover down to a minimum and have the area around the palm trees kept clean. So, there is no definite outake on that it seems.

It is hard to know when a tree has the disease and usually by the time one sees the outward signs, it is too late. The tree that has the disease most likely will exhibit one or more of the following:

1. Coconuts, mature and immature, begin to drop from coconut palms and the fruit begin to drop from other varieties, a process called ‘shelling’.

2. Flower stalks (inflorescences) begin to blacken.

3. Palm fronds start to yellow (or, in the case of some species, turn greyish-brown), beginning with the older, lower fronds and progressing up through the crown.

4. The spear leaf collapses and the bud dies. By the time that this happens, the tree is already dead.

5. The entire crown falls from the tree leaving a forlorn ‘telephone pole’ stalk.

Through research and the shared information of friends, we purchased the oxytetracycline to inject our trees. Others had started their injections a year or two ago. Late last year we lost 3 palms on the beach and decided to finally take some preventive measures. We found a website where we bought the chemicals and they were shipped to us. The cost of this program is about $5.00 per tree per year (injecting them every 3 months).

First, a hole is drilled into the trunk of the tree. There must be trunk showing to accept the liquid via the container placed in the hole. Newer palms that are still sprouting fronds do not show a trunk and we by-pass them for the time being.

Into this hole, a "bullet" type object is placed. This has a foam core which accepts the needle of the syringe for the the liquid to be injected. The bullet is used twice; the first time it is pounded in only half way and then the liquid is injected. The second time (3 months later) it is removed and the hole drilled slightly deeper, reinserted and then the liquid can be injected.

The program does not always work as I mentioned before it is hard to tell if the palm tree has already become infected. We have lost about 5 trees since we started the program in January and we assume they had already been infected but no outward signs were evident.

We have about 65 palm trees and it takes about 1 1/2 hours (after the initial drilling has been done) to inject all the trees. We will continue this process in hopes that we can save our trees.

In the meantime, everytime we lose a palm, we replant a new one hoping that eventually we can beat this thing!