What is Lethal Yellowing?
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. The good news is that palms native to Florida are generally resistant to this disease.
Lethal yellowing gets its name from the yellowing and drooping of palm fronds beginning with the lower fronds and advancing up through the crown. The disease characteristically has the following progression:
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.
Unless treated, the tree dies within three to six months of the first symptom.
The cause of lethal yellowing is believed to be a bacteria-like organism called a phytoplasma. Phytoplasmas are not yet well understood but, like bacteria, they can be controlled with antibiotics, in this case, oxytetracycline.
The Spread of the Disease
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.
What To Do
There is to date no cure for lethal yellowing. Quarterly injections of oxytetracycline can keep the disease in check and this may be an option for extremely valuable residential landscape palms. Check with your local tree care specialist for advice regarding the cost and procedure in your area. The best option in combating lethal yellowing is to plant palms resistant to the disease.
Popular Native Palms Resistant to Lethal Yellowing
Cabbage Palmetto (Sabal palmetto)
Florida Thatch Palm (Thrinax radiata)
Key Thatch Palm (T. morrisii)
Common Imported Palms Resistant to Lethal Yellowing
Alexandra Palm (Archontophoenix alexandrae)
Carpentaria Palm (Carpentaria acuminata)
Yellow Cane Palm (Chrysalidocarpus lutescens)
Pygmy Date Palm (Phoenix roebelenii)
MacArthur Palm (Ptychosperma macarthurii)
Solitaire Palm (Ptychosperma elegans)
Mexican Washingtonia (Washingtonia robusta)
Foxtail Palm (Wodyetia bifurcata)
Queen Palm (Syagrus romanzoffianum)