Keep it Green, by Michael Womack
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Saturday, August 4, 2001

Inspect for palm yellowing disease

Lethal yellowing has been confirmed in Corpus Christi date palms. Although we knew there were trees that appeared to be afflicted along the Corpus Christi bayfront, there was reason to believe that the dieback might have a different cause. Unfortunately, that wasn't the case.
   Trunk tissue samples collected from Canary Island date palms near Ocean and Hewit drives were sent to Dr. Nigel Harrison, plant pathologist at the University of Florida.
   Harrison uses a genetic screening procedure to test for the organism responsible for lethal yellowing. Preliminary tests have found PLOs similar to those that cause lethal yellowing.
   Further tests are being conducted to see if it is the same strain responsible for lethal yellowing in Florida coconut palms.
   Richard Maxwell of TreeSaver, Inc. in Royal Palm Beach, Fla., has been working with the disease for 24 years.
   Maxwell noted that different strains of the disease-causing organism have been detected, sometimes making it difficult to get positive identification of the disease.
   Planthopper attack
   The disease-causing organism is spread by planthoppers, tiny brown insects that suck the juices from young palm leaves. The organism that causes the disease must be ingested by the insect in order to be transferred from tree to tree.
   As the insect begins feeding on a new plant, it injects juices from its stomach, including the organism that causes lethal yellowing.
   It would seem logical that controlling the insects would prevent the disease. But planthoppers are extremely small and difficult to detect. They also tend to feed on young leaves of palms that are often over 30 feet tall.
   It appears that area date palms were probably infected several months ago. The recent spike in temperatures combined with limited rainfall have stressed the palms and caused rapid progression of symptoms. Infected palms have shown considerable frond dieback in the past two weeks.
   Incurable disease
   Unlike most diseases, it cannot be spread though pruning tools.
   Once a tree is infected, there is no cure. Repeated treatments of the antibiotic oxytetracycline hydrochloride (OTC) will usually result in remission of symptoms if applied in the early stages of the disease.
   These injections must be repeated every three to four months or the symptoms will return. OTC is actually considered to be more effective as a preventative measure in regions where lethal yellowing has been identified.
   The Treesaver injection process was specifically developed to effectively deliver antibiotics to plants such as palms. Maxwell, owner of Treesaver, Inc. informed me that Pest Fog is the only company in the Texas Coastal Bend currently using his system.
   Ocean Drive disease
   Date palms that are currently showing symptoms of severe frond dieback may already be too far gone. It may be better to simply remove trees in areas where the disease is apparent and confirmed, which is only Ocean Drive area at this time. Visual inspection of date palms in surrounding areas including western Nueces County, Flour Bluff, North Padre Island, Port Aransas, Portland and Corpus Christi Beach showed no sign of lethal yellowing.
   It is important that all precautions are made by landowners to minimize the spread of the disease through preventative injections of trees in infected regions and through timely tree removal of dead palms.
   If the disease isn't controlled quickly, we could be facing a similar fate as the lower Rio Grande Valley. Dr. Marvin Miller, a Texas A&M University plant pathologist in Weslaco noted that most of the old, majestic Canary Island date palms are now dead due to the outbreak of lethal yellowing in Brownsville in the early 1980s.
   With a little luck and the timely action of local homeowners, we will hopefully minimize the impact of this disease and keep the statuesque beauty of these palms in our community.
  
  

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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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