Keep it Green, by Michael Womack
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Saturday, July 21, 2001

Palm disease may be culprit in Ocean Drive tree deaths

Palms at risk High RISK: The Canary Island date palms Moderate Risk True date palms (P. dactylifera) Windmill palms (Trachycarpus fortunei) Slight Risk: Senegal date palms  (Phoenix reclinata) Wild date palms  (P. sylvestris) Chinese fan palms  (Livistona chinensis)

Lethal yellowing is a devastating plant disease that can strike palms, including the stately Canary Island date palm. This week, palm trees near the intersection of Hewit and Ocean drives have shown symptoms of the disease. Although the trees haven't yet been diagnosed with the disease, Coastal Bend homeowners can benefit by learning about the symptoms and treatments of lethal yellowing.
   Lethal yellowing is caused by a single-celled organism that is transferred from palm to palm by a flying planthopper that feeds on palm sap.
   The organism can only be spread by the insect. Lethal yellowing cannot be transmitted through pruning equipment. The first symptom is fruit or nut drop followed by browning and death of the fruiting structures. In infected Canary Island date palms, the brightly colored orange branches that are usually covered with dates eventually die.
   In the next stage, date palms show browning and drying of lower leaves that quickly progress until all of the leaves are dead. These symptoms in date palms are slightly different than the characteristic yellowing of leaves in coconut palms. About halfway through the this stage, the crown or growing point will die. At that point, the palm is dead.
   'Closed-umbrella'
   The dead leaves will initially collapse against the tree trunk producing a "closed-umbrella" effect. Later, they will fall, leaving only the trunk of the trees as they enter the final, "telephone pole" stage. The entire process typically takes three to six months. Once a tree is infected, there is no cure. Repeated treatments using a special antibiotic (oxytetracycline hydrochloride, or OTC) will cause symptoms to go into remission, but only if it is injected into the palm during early disease stages. Injections must be repeated every three to four months or the symptoms will return. As soon as injections are terminated, infected palms will die within six months.
   Prevent spreading
   OTC is actually considered to be more effective as a preventative measure in regions where lethal yellowing has been identified.
   Once the disease is discovered in an area, it usually progresses until it kills all the susceptible palms in the vicinity. Removing infected palms also helps to avoid the further spread of the disease.
   We do not yet know if lethal yellowing has struck the Nueces County area as it has in parts of Florida. The Nueces County Agricultural Extension Service is awaiting lab results.
   Lethal yellowing was first reported in Jamaica about a century ago in coconut palms. It entered the U.S. through Key West and had a significant presence in mainland Florida by the mid 1950s. Lethal yellowing was introduced into Brownsville in 1979, probably on infected palms shipped in from Florida. It killed a significant number of Canary Island date palms (Phoenix canariensis) and true date palms (P. dactylifera) in the Rio Grande Valley before it was brought under control in the 1980s.
  
  

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Michael Womack is a horticulturist with the Texas Agricultural Extension Service. Got a question? Michael Womack will answer landscape and gardening questions. Call 886-4648, category 3025 to record your question. Write Keep It Green, Corpus Christi Caller-Times, P.O. Box 9136, Corpus Christi, TX 78469 or email wm-womack@tamu.edu

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