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UGA Citrus Greening Survey Results (Spring 2019)

Figure 1. Map of Georgia counties where citrus samples have been collected and tested for CLas. Grey indicates counties surveyed in 2019 with no CLas-positive samples, while CLas-positive samples have been detected in counties shown in red. (Note: Chatham Co. not surveyed in 2019, but previous USDA testing indicated CLas-positive trees.)

Survey Information:

In Spring 2019, a team of UGA extension specialists and agents initiated a survey of select residential and commercial citrus sites in southern and coastal Georgia to investigate the prevalence of Candidatus liberibacter asiaticus (CLas), the bacterium that causes citrus greening disease. Citrus leaf samples were collected during May through August 2019 and submitted to the UGA Plant Molecular Diagnostic Laboratory in Tifton. In total, 94 samples were tested for CLas from 8 commercial and 21 residential sites in 11 Georgia counties (Table 1; Figure 1). In total, 8/94 (9%) samples tested positive for CLas , with 4/11 (36%) counties and 5/29 (17%) sites having at least one positive sample. Three of the counties where CLas positive trees were detected in 2019 (Lowndes, Pierce, and Bryan) had not been previously known to have CLas positive trees. The eight samples testing positive for CLas came from five non-commercial sites. These consisted of four residential sites and one public school site.

Citrus Greening:

Citrus greening disease (Figure 2) or huanglongbing (HLB) is caused by the bacterium Candidatus liberibacter asiaticus (CLas). This bacterial species is vectored by the Asian citrus psyllid (ACP), an invasive species first found in residential citrus in southern Florida in 1998. CLas inhibits the flow of nutrients throughout the tree, causing premature fruit drop, lower fruit quality, and higher tree mortality. Since first being detected in 2005, HLB has spread throughout Florida, where it is estimated that over 80% of Florida’s citrus trees are currently infected. This has led to a more than 70% decline in citrus production. If greening were to establish in Georgia, it would become a grave threat to Georgia’s fledgling citrus industry. Though Georgia is currently under USDA-APHIS quarantine, extensive HLB surveys have not been conducted. Prior to 2019, small surveys have indicated the presence of HLB in Camden and Chatham counties, but only in residential trees, not commercial citrus. The psyllid vector has been previously found in all coastal counties in Georgia (Figure 3), and was found in Lowndes and Charlton counties in 2018.

Figure 2. Citrus greening symptoms in Camden County, GA. Photo by J. Oliver.

Figure 3. Asian citrus psyllid in Camden County, GA. Photo by J. Oliver.


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About Jonathan Oliver

Dr. Jonathan Oliver is an Assistant Professor and Extension Specialist in the Department of Plant Pathology at the University of Georgia. He has a 75% research and 25% extension appointment. Dr. Oliver started in his current position at the University of Georgia in mid-2017 as an extension fruit pathologist at the Coastal Plains Experiment Station in Tifton, Georgia. His responsibilities include research and extension activities focused on pathogen biology and disease management in fruit crops grown primarily in the southern part of Georgia, including blueberries, blackberries, citrus, and other emerging fruit crops. Dr. Oliver obtained a BS degree in Plant Pathology and Microbiology & Cell Science from the University of Florida in 2005, and a PhD in Plant Microbe Biology from Cornell University, New York State Agricultural Experiment Station in Geneva, NY in 2011. In addition, he has also been postdoctoral researcher at Kansas State University and Auburn University. At Auburn, he characterized the interactions between the emerging bacterial pathogen, Xylella fastidiosa, and its blueberry plant hosts. He currently serves as a Plant Pathology Section editor for the Southeast Regional Blueberry Integrated Management Guide.