Lethal Yellowing Can Cost You the Green
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 even 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, a tetracycline used for the treatment of infections.
But wait – we have some good news: palms native to Florida are generally resistant to lethal yellowing.
Symptoms of Lethal Yellowing
Lethal yellowing gets its name from the yellowing and drooping of palm fronds beginning with the lower fronds and advancing up through the crown. Unless treated, the tree dies within three to six months of the first symptom.
The progression of lethal yellowing is typically as followed:
- Coconuts, mature and immature, begin to drop from coconut palms and the fruit begin to drop from other varieties, a process called shelling.
- Flower stalks (inflorescences) begin to blacken.
- 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.
- The spear leaf collapses and the bud dies. By the time that this happens, the tree is already dead.
- The entire crown falls from the tree leaving a forlorn “telephone pole” stalk.
The Cause of Lethal Yellowing
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 Spreading of Lethal Yellowing
While there is no definitive proof as of yet, the lethal yellowing microorganism 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 if Your Tree is Suffering from Lethal Yellowing
There is no real 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 tree care company in Palm Beach County for additional advice regarding the cost and lethal yellowing 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)
- Royal Palm (Roystonea regia)
- Paurotis Palm (Acoelorraphe wrightii)
- 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)