Sign up for the iWire to get breaking news, event info and the species spotlight.

Go Back | Printer Friendly Fact Sheet

Candidatus Liberibacter asiaticus

Citrus Greening (Huanglongbing)

Class: Alpha Proteobacteria
Order: Rhizobiales
Family: Phyllobacteriaceae

Photographer: Hilda Gomez, USDA


Huanglongbing (HLB) in Chinese literally translates to Yellow Dragon Disease and it is caused by phloem-limited bacterium. That means that this bacterium attacks the phloem system of plants which is like the circulatory system in animals. This bacterium is carried to host plants by an insect vector, for Huanglongbing it is the psyllid insect Diaphorina citri.

Establishment and Symptoms of Citrus Greening on
Leaves of newly infected trees develop a blotchy mottle appearance. On repeatedly infected trees, the leaves are small and exhibit asymmetrical blotchy mottling. Fruit from HLB-infected trees are small, lopsided, poorly colored, and contain aborted seeds. The juice from affected fruit is low in soluble solids, high in acids and abnormally bitter. The fruit retains its green color at the navel end when mature, which is the reason for the common name citrus greening disease. This fruit is of no value because of poor size and quality. Please look at the USDA Flickr page for various pictures showing the symptoms of Citrus Greening

If you believe you have Citrus Greening in your citrus trees, please report this species.


Host(s): Citrus (lemon, lime, orange, grapefruit, kumquats etc.) In Texas, we are most concerned about the threat to Citrus plants both in our backyards and those used for commercial production.

Ecological Threat: There are three forms of greening that have been described. The African form produces symptoms only under cool conditions and is transmitted by the African citrus psyllid Trioza erytreae, while the Asian form prefers warmer conditions and is transmitted by the Asian citrus psyllid Diaphorina citri. The American form (discovered first in Brazil) originated in China, so symptoms show under warmer conditions and it is transmitted by Diaphorina citri. HLB is known to occur in Florida, Louisiana, South Carolina, Texas and Georgia. HLB has caused a loss of 100.000 citrus acres in its first year (2005-2006) in Florida alone. For Florida, almost the entire state has established infection of Huanglongbing. As of 2021 in Texas, this disease has been detected in several areas throughout the state. The Texas Department of Agriculture (TDA) has instituted citrus quarantines to prevent the spread. Quarantined areas include: counties throughout Coastal Bend, Laredo, Rio Grande Valley and Gulf Coastal areas including Houston metroplex. For more information on the Asian Citrus Psyllid (Diaphorina citri) click here

Biology: The psyllid Diaphorina citri, transmits the bacteria when they feed on an infected plant and then feed on an uninfected citrus plant. The bacteria can be acquired by the insects in the nymphal stages and the bacteria may be transmitted throughout the lifespan of the psyllid.

History: HLB is one of the most devastating diseases of citrus and since its discovery in Florida in 2005, citrus acreage in that state has declined significantly. In April 2012, after about a week of testing, the California Department of Food and Agriculture (CDFA) removed a pumelo tree with a lemon graft from Los Angeles County after the tree and an Asian citrus psyllid found on the tree both tested positive for Huanglongbing. In late 2012, the presence of HLB was confirmed in south Texas, where some orchards are now quarantined to prevent the infection from spreading. In just 7 short years this disease has spread to 7 states, including Texas, California and Florida that are crucial for the citrus industry.

The Texas Department of Agriculture has quarantined Aransas, Brazoria, Brooks, Calhoun, Cameron, Fort Bend, Galveston, Harris, Hidalgo, Jim Hogg, Kenedy, Kleburg, Montgomery, Nueces, Starr, Webb and Willacy Counties.

U.S. Habitat: Where citrus trees grow, in states that are subtropical and maintain humidity levels above 50%.


Native Origin: Southeast Asia

U.S. Present: CA, FL, GA, HI, LA, SC and TX

Distribution: Now the Texas Department of Agriculture has quarantined 17 counties throughout the state. Quarantined zones include Rio Grande Valley, coastal Bend and Gulf Coastal counties including the Houston area.


The yellowing of leaves can also be caused with over-watering of Citrus. However, if fruit production becomes asymmetrical and sour that is a strong indicator of Citrus Greening.


Informed citizens who adhere to citrus quarantines are necessary to stop the spread of Citrus Greening and Asian Citrus Psyllid to more counties throughout our state.

TISI has a Citrus Greening and Asian Citrus Psyllid education program. We are providing educational workshops on symptom detection, psyllid trapping services, in-field citrus greening detection and molecular analyses of samples. PLEASE click here to contact us for more information. Yellow "sticky card traps" are placed in citrus trees in residential or commercial properties, both the color and the pheromones on the trap attract the psyllids to it. If the Asian citrus psyllid is found on a tree the next step is to analyze the populations for Huanglongbing. Thankfully, both adults and nymphs are also susceptible to insecticides.

Asian citrus psyllid populations in Florida have many generalist predators such as spiders, lacewings, hover flies and minute pirate bugs. Two lady beetles, Olla v-nigrum and Harmonia axyridis, are the most important predators of Asian citrus psyllid nymphal populations in Florida. They consume the nymph stage of the psyllid and interrupt the insect 's lifecycle altogether.


Google Search: Candidatus Liberibacter asiaticus
Google Images: Candidatus Liberibacter asiaticus
NatureServe Explorer: Candidatus Liberibacter asiaticus
Bugwood Network Images: Candidatus Liberibacter asiaticus


da Graça, J. V.; Kunta, M.; Sétamou, M.; Rascoe, J.; Li, W.; Nakhla, M. K.; et al.(2015). Huanglongbing in Texas: Report on the first detections in commercial citrus. Journal of Citrus Pathology, 2(1)

Duan, Y., Zhou, L., Hall, D. G., Li, W., Doddapaneni, H., Lin, H., ... & Gottwald, T. (2009). Complete genome sequence of citrus huanglongbing bacterium, Candidatus Liberibacter asiaticus obtained through metagenomics. Molecular Plant-Microbe Interactions, 22(8), 1011-1020.

Gottwald, T. R. (2010). Current Epidemiological Understanding of Citrus Huanglongbing*. Annual review of phytopathology, 48, 119-139.

Louzada, E. S., Vazquez, O. E., Braswell, W. E., Yanev, G., Devanaboina, M., & Kunta, M. (2016). Distribution of Candidatus Liberibacter asiaticus Above and Below Ground in Texas Citrus. Phytopathology, 106(7), 702-709.

Manjunath, K. L., Halbert, S. E., Ramadugu, C., Webb, S., & Lee, R. F. (2008). Detection of Candidatus Liberibacter asiaticus in Diaphorina citri and Its Importance in the Management of Citrus Huanglongbing in Florida. Phytopathology, 98(4), 387-396.

Data Source

Last Updated: 2024-02-01 by Ashley Morgan-Olvera, Texas Invasive Species Institute