EPLP-012 6/14

Date Palm Lethal Decline in Texas Landscapes

Molly Giesbrecht, Extension Associate1 Greta Schuster, Professor2 Kevin Ong, Associate Professor and Extension Plant Pathologist1

In the late 1970s, a lethal disease of palm trees first presence of the disease, since other diseases and stress appeared in the Rio Grande Valley. The symptoms factors can cause many of the same symptoms. resembled those of the phytoplasma-caused lethal yel- 1. Typically, the first symptom on mature, lowing disease already well-documented in Africa, the fruit-bearing trees is the dropping of most or all Caribbean, and Florida. Electron microscopy showed of their fruit within a few days (Fig. 1). phytoplasma cells in the phloem (vascular) tissues of 2. A red to brown necrosis (death of the plant the infected palms, which led to the presumption that tissue) of the oldest leaves can occur simultane- the disease was caused by the lethal yellowing phyto- ously or follow next, progressing from leaf tips to plasma. the base of the leaves. In 2001, many palms in the Corpus Christi area 3. On Phoenix palms, after the first set of oldest exhibited the same symptoms and began declining. leaves die, the central spear leaf dies. This is the In 2002, the disease was identified as a phytoplasma most indicative symptom associated with this distinct from, but related to, the lethal yellowing disease. phytoplasma. Now known as date palm lethal decline (DPLD), Texas Phoenix palm decline, or lethal decline, it is the only known phytoplasma disease of palms in Texas. It affectsPhoenix spp., Syagrus romanzoffiana, and Sabal palmetto palms and is present in Bexar, Cameron, Harris, Hidalgo, Kleburg, Nueces, and Wil- lacy counties. Phytoplasmas are a specialized group of bacteria that infect only plants. They belong to the class Molli- cutes, have no cell wall, and cannot survive outside of a living host. Phytoplasmas cause disease on a wide range of plant hosts and are typically transmitted by leafhop- per and planthopper insects. The specific vector (the insect that transmits the bacteria) or vectors for this disease have not been determined. Symptoms The disease symptoms progress in a chronological order. Both the combination of symptoms and their progression are important in evaluating the possible

1. Texas A&M AgriLife Extension Service, The Texas A&M University System 2. Texas A&M University–Kingsville Figure 1. Loss of fruit from a Phoenix canariensis. 4. Although it may often go unnoticed, moderate Management to extensive root necrosis and decay typically Sample and test symptomatic host trees. If a tree is occurs by this time, sometimes to the extent that positive, report the results to the Texas Department of the tree can be rocked back and forth by push- Agriculture and remove the tree. To prevent infection ing on the trunk. Trees affected by this patho- in areas known to have had the disease, healthy trees gen have more extensive root decay than trees can be treated with trunk injections of oxytetracycline affected by the lethal yellowing phytoplasma. HCl. To remain effective, repeat the applications every 5. The remaining leaves will continue to die pro- few months for the remaining life of the tree or as long gressively from the lower crown upward (older as there is a threat of infection. leaves to younger leaves) (Fig. 2). Quarantines are established in areas where the dis- 6. The tree will die completely within a year. ease is prevalent and around confirmed infected trees Phoenix canariensis, P. dactylifera, P. sylvestris, to restrict moving susceptible host tree species out of P. reclinata, P. roebelenii, Sabal palmetto, and Syagrus these areas. As of May 2014, all of Cameron, Hidalgo, romanzoffianapalms can host this disease. In Texas, Nueces, and Willacy counties are under quarantine as the most frequently affected species is P. canariensis well as sections of Bexar, Harris, and Kleburg counties. because it is widely used in landscape plantings and is Quarantine regulations require that susceptible to this disease. • Susceptible trees within a 1-mile radius of an Nurseries can monitor quarantined palms grown infected tree remain stationary for 6 months and in Texas and coming from out of state. Sample sus- treated with insecticides for vector control for 3 pected trees according to the protocol TPDDL WI 2.47 months after the quarantine begins. Sampling Palms for Phytoplasma Detection and send • Susceptible host trees within 2 miles of a con- the sample to the Texas Plant Disease Diagnostic Lab firmed infected tree must also be treated with for testing. The laboratory uses molecular methods to insecticides for vector control for 3 months determine the presence of phytoplasma.* before the tree can be moved. They also must be treated within 48 hours before being moved and inspected for disease symptoms within 24 hours after being moved. • Susceptible host trees outside of the 2-mile radius around the infected tree(s) but within the estab- lished quarantine zone must be treated for vector control for 6 weeks before being moved, treated within 48 hours of being moved, and inspected within 24 hours after being moved. Visit the websites below for more detailed informa- tion on regulations regarding this disease. http://www.texasagriculture.gov/Regulatory Programs/Quarantines.aspx http://www.texasagriculture.gov/Regulatory Programs/PlantQuality/PestandDiseaseAlerts.aspx

*For sampling protocols and/or further information regarding this Figure 2. Death of the lower leaves of a Sabal palmetto disease, contact Kevin Ong at the Texas Plant Disease Diagnostic infected by date palm. Photo by Jorge Lozano. Laboratory at (979) 845-8032.

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