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fact sheet Huanglongbing (HLB)

itrus greening or Huanglongbing (HLB) is a devastating disease of worldwide (Gottwald et al., 2007). HLB is particularly devastating because of its severe yield reduction in citrus Ctrees, followed by tree decline, the absence of resistant citrus varieties, and the limited control measures to prevent disease progression and pathogen spread by the vector, Asian citrus psyllid (ACP, Diaphorina citri). At its current rate of spread and impact on the economics of , HLB could destroy the U.S. citrus industry in our lifetimes. With current management technology, early detection is critical to the rapid response needed to slow the spread of the disease.

The disease was first identified in imperfect control measure that tends in 2005 and is now present throughout to slow the spread of the disease rather Florida citrus producing counties. The than stop it and only works when practiced causal agent is the phloem-limited bacte- in conjunction with scouting to identify rium, Candidatus asiaticus and remove infected trees. Unless an (Las). ACP was first discovered in 1998, effective, comprehensive eradication but it was too widespread to consider program is in place to kill the vector, an eradication program (Halbert (et al., infected psyllids will migrate to infect 2002). HLB was discovered in August new plants, especially when there are 2005, 7 years after the vector, and within abandoned groves of infected plants in a few months the disease was detected the area to serve as inoculum reservoirs. HLB image courtesy of ipmimages.org in several counties in South Florida. The In Florida, reducing disease spread by pathogen spread quickly throughout the vector control alone has had limited Florida citrus-growing regions and, as a effectiveness such that the statewide HLB enced an even greater drop, going from result, a mass tree removal to control the incidence is estimated at over 50 percent a peak of about 14 million trees to the bacterium was not considered a viable and nearing 100 percent in many areas. current approximately 5 million trees. option. ACP has since been found in six New tree plantings are at a historically other Southern states, Hawaii, and most The citrus industries in Florida and low level and are replacing only about recently in . The psyllid first California contribute more than $10 billion 50 percent of trees that are lost appeared in Southern California in 2008, to their states’ economies. Since its to HLB and other decline diseases. Citrus and HLB was detected in 2012 in a pum- introduction, HLB has had a devastating nurseries can supply only about 50 percent melo tree in a yard in Los Angeles County. impact on Florida’s citrus industry. of new trees required for replanting. Based ACP was recently reported in citrus Commercial citrus acreage has shrunk on recent observations, protecting replants groves in California’s Central Valley. to 524,640 acres as of the fall of 2013, from psyllid infection with systemic and a 30 percent decline from 748,555 acres topical insecticides has been only partially The HLB pathogen is a particularly difficult before the was successful. Economically sustainable organism to control. The bacterium is discovered in 2004. That’s the lowest production after trees show symptoms essentially inaccessible by chemical citrus acreage figure since the USDA began at age 4 or 5 has not yet been demonstrat- treatments because it is protected deep the survey work back in 1966. From a tree ed. In light of the Florida experience, the inside the plant’s vascular tissue. Las is perspective, the number of orange trees in citrus industry is gravely concerned that disseminated through grafting and insect the state has declined from about 80 HLB will have a similar impact in California. transmission by ACP (Halbert & Manju- million down to the current approximately continued >> nath, 2004). Vector control alone is an 60 million trees. has experi-

The National Plant Diagnostic Network (NPDN) provides a cohesive, distributed system to quickly detect and identify pests and pathogens of concern. To learn more about NPDN, visit www.npdn.org | NIFA invests in and advances agricultural research, , and extension and seeks to make transformative discoveries that solve societal challenges. Learn more by visiting www.nifa.usda.gov or following @USDA_NIFA on Twitter. | USDA is an equal opportunity provider and employer • May 2016 fact sheet: Huanglongbing (HLB) (continued)

The National Plant Diagnostic Network Graham, J. H. 1995. Root regeneration (NPDN) is a critical capacity resource for and tolerance of citrus rootstocks to root the biosecurity of the United States. rot caused by nicotianae. NPDN supplements the resources of plant Phytopathology 85, 111-117. diagnostic laboratories capable of providing diagnoses and screening for ACP and HLB. Graham JH, Johnson EG, Gottwald TR, In addition, the NPDN coordinates diag- Irey M, 2013. Pre-symptomatic fibrous nostician training in the most up-to-date root decline in citrus trees caused by methods for HLB diagnostics in coopera- huanglongbing and potential synergistic tion with USDA Animal and Plant Health interaction with Phytophthora spp. Inspection Service’s Plant Protection Plant Disease 97, 1195-9. and Quarantine. These services enable Halbert SE, Manjunath KL, 2004. rapid and accurate diagnoses for dealing Asian citrus psyllids (Sternorrhyncha: with this devastating disease. Psyllidae) and greening disease of citrus: A literature review and assessment of risk Literature cited in Florida. Florida Entomologist 87, 330-53.

Belasque J, Bassanezi RB, Yamamoto PT, Johnson EG, Wu J, Bright DB, Graham et al., 2009. Factors associated with JH, 2013. Association of ‘Candidatus control of huanglongbing in Sao Paulo, Liberibacter asiaticus’ root infection, : a case study. Proceedings of the but not phloem plugging with root loss Proceedings of the International Research on huanglongbing-affected trees prior Conference on Huanglongbing, 2008. to appearance of foliar symptoms. Orlando, Florida. in press.

Bassanezi, R. B., Montesino, L. H., Kant S, Bi YM, Zhu T, Rothstein SJ, 2009. Gasparoto, M. C. G., Bergamin Filho, A., SAUR39, a Small Auxin-Up RNA Gene, and Amorim, L. 2011. Yield loss caused Acts as a Negative Regulator of Auxin by huanglongbing in different sweet Synthesis and Transport in . Plant orange in São Paulo, Brazil. Physiology 151, 691-701. Eur. J. Plant Pathol. 130:577-586. Kim JS, Sagaram US, Burns JK, Li JL, Bové JM, 2006. Huanglongbing: Wang N, 2009. Response of Sweet A destructive, newly-emerging, century- Orange (Citrus sinensis) to ‘Candidatus old disease of citrus. Journal of Plant Liberibacter asiaticus’ Infection: Pathology 88, 7-37. Microscopy and Microarray Analyses. Da Graça JV, 1991. Citrus greening Phytopathology 99, 50-7. disease. Annual Review of Phytopathology Schneider H, 1968. Anatomy of 29, 109-36. Greening-Diseased Sweet Orange Shoots. Etxeberria E, Gonzalez P, Achor D, Albrigo Phytopathology 58, 1155-60. G, 2009. Anatomical distribution of abnormally high levels of starch in HLB- affected trees. Physiological and Molecular Plant Pathology 74, 76-83.