Phytoplasma Diseases of Palms in the USA
Robert R Krueger1 and Brian W Bahder2
1USDA-ARS National Clonal Germplasm Repository for Citrus & Date, Riverside, CA
2Dept of Entomology & Nematology, University of Florida Fort Lauderdale Research & Education Center, Davie, FL
Phytoplasmas are plant pathogenic bacteria that lack cell walls and have reduced genomes. Their taxonomy has historically been based upon 16S ribosomal gene sequences. Since they have not been cultured to date, they are classified as Candidatus Phytoplasma spp. Phytoplasmas of various taxonomic designations have been associated with or shown to cause diseases in a wide range of cultivated and wild plant species. In recent years, long-established and newly reported declines or diseases of palms have been associated with phytoplasmas. Although there are reports of phytoplasma-associated diseases of palms in both the Eastern and Western Hemispheres, this brief review will focus on reports from the United States.
The earliest reported disease of palms that was later associated with Phytoplasma infection was Lethal Yellows (LY). LY is a disease which attacks and kills coconut palms (Cocos nucifera). LY was first reported in Jamaica in 1891 and much later (1972) associated with a phytoplasma (Tsai and Harrison 2003), which was later identified as being in the taxonomic sub-group 16SrIV-A (Harrrison et al. 2002a). An epiphytotic of LY occurred in southern Florida in the 1960's to 1970's (Tsai and Harrison 2003). During this outbreak Phoenix spp., which in Florida were planted as ornamentals or present in germplasm collections or botanic gardens were also shown to be susceptible. This was evidenced by the presence of mycoplasma-like bodies observed in tissues via electron microscopy (Thomas 1974, 1979; Howard et al. 1979). Phoenix dacytlifera was more susceptible to decline than other Phoenix spp., being equivalent in this regard to C. nucifera (Howard and Barrant 1989), although the symptomology was distinct compared to that in C. nucifera (McCoy et al. 1983). The vector of LY in Coconut palm was demonstrated to be the planthopper Haplaxius crudus van Duzee, and this was assumed to be the vector transmitting LY to Phoenix spp. as well (Howard et al. 1983, 1984).
There's a lot more to this story: https://ceventura.ucanr.edu/Com_Ag/Subtropical/?newsletteritem=100493
Foliar yellowing symptoms of Lethal Yellows on Coconut palm. Photo credit: NA Harrison
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Palm trees are commonly seen in California, making some think about the tree-lined streets of Hollywood, or sitting by the pool somewhere. These tropical or subtropical trees are beautiful and varied, with many different types of palms, each adapted for different growing conditions and each with specific disease-causing pathogens that can attack it.
Palm trees, like other plants, are susceptible to pathogens that can weaken or even kill the tree. Diseases such as diamond scale, pink rot, Fusarium wilt, and others can reduce the leaf canopy, discolor leaves and trunk, and cause distortion, stunting or death.
If you have palm trees or care for palms as part of your work, it's important to identify and know about these diseases and maintain healthy trees so they don't succumb to these potentially lethal issues.
Learn more about disease identification, selecting the right palms, and management for palms in UC IPM's recently updated Pests Notes: Palm Diseases in the Landscape by Donald Hodel, Environmental Horticulture Advisor with the University of California Cooperative Extension, Los Angeles County.
What's different in this version? Many new photos have been added along with a new section with information on petiole and rachis blights and tips to maintain healthy, vigorous palms.
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[From the August 2016 issue of the UC IPM Green Bulletin]
The South American palm weevil (SAPW), Rhynchophorus palmarum, was recently discovered in a Canary Island date palm in San Ysidro, southern San Diego County.
Twenty additional Canary Island date palms in the San Ysidro area appear to be infested, but have not yet been confirmed.
Weevil Biology
The biology of SAPW is similar to the red palm weevil that was eradicated from Laguna Beach, Orange County, between 2010–2012.
The SAPW, native to Mexico and Central and South America, destroys the apical growth of the palm by feeding on the growing tissue in the palm crown, eventually killing the palm (Figure 3). This differs from the symptoms of fusarium wilt which causes dying of lower branches.
Symptoms and Signs
Signs of the pest include accumulated frass (insect excrement) at the base of the leaves and pupal cases on the ground near the tree. Holes and tunneling can also be found at the base of palm fronds.
In addition to Canary Island date palms, the South American palm weevil is also known to attack coconut palms, date palms, and the king sago palm in the cycad family.
It is believed that the spread of this pest can be delayed with the fast detection and removal of infested trees. Chipping (Figure 4), burning, and burying infested material deeply can reduce the likelihood that SAPW will emerge and escape from infested palms.
Report a Find
-Jennifer Pelham, UCCE Area Environmental
Horticulture Advisor UCCE San Diego & Orange counties,
jlpelham@ucanr.edu;
-Tracy Ellis, Agricultural Entomologist, County of San Diego, Tracy.Ellis@sdcounty.ca.gov
/h2>/h2>/h2>/span>- Author: Jeannette E. Warnert
Reporter Michael Cabanatuan spoke to Donald Hodel, UC Cooperative Extension advisor in Los Angeles County, about the trees' suitability for the Bay Area's fog, wind, salt air and water. The Bay Area climate, Hodel said, is not unlike that of the Canary Islands. The palms are well suited to grow in the San Francisco-Oakland area.
"But because of their quintessential look, it's hard for some people to get over the fact that palms are not just for the tropics," he said.
CalTrans senior landscape architect Clive Endress said the trees make a connection from the bridge to the shore.
"We decided we'd do it with trees to emphasize the start of the bridge and the end of the bridge," Endress said.