Tuesday Talks with Dr. Patterson

January 20, 2015

Citrus Greening and Future Challenges

There is a growing appreciation of the challenge to increase food production for a growing world population.  It should also be appreciated that this challenge will likely be even more challenging given the likely outcome of scarcer production resources (land and water), production systems that are disrupted by climate change, and new diseases afflicting plants, animals, and man.  The disease the citrus industry now faces, known commonly as citrus greening, is a good example of the types of disease pressures we will face in the future.  The industry’s response to this disease may also provide a model for future disease challenges.  

Citrus greening is the common name given the disease Huanglongbing (HLB).  It is a disease caused a bacteria that infects citrus trees.  It is transmitted by an insect, the Asian Citrus Psyllid.  It is described as citrus greening because fruit on infected citrus trees fails to mature and ripen and remains small and green and as a result is inedible.  The disease infects the phloem of the tree and moves into the roots.  Root function is compromised by the disease as the roots degrade and die.  The foliage on the infected trees is a pale green and is not as dense and full as healthy trees.  The fruit yield declines and ripening fruit is dropped prematurely.  The disease was first identified in China in 1919, though it was not fully understood at that time.  Since then, it has spread through Asia, Africa, and South America.  It was reported in Brazil, a major global orange producer, in 2004.  In 2005 it was found in Dade County, Florida (Miami area).  Since then, it has spread to infect all citrus producing counties in Florida and is now reported in Texas and California.  At present, there is no cure for this disease.  There is no effective antibacterial agent and there are no commercially viable disease-resistant varieties or root stock.  Root stock is important because all citrus trees are grafted onto root stock. (University of Florida) 

The impact of citrus greening is dramatic.  Once the tree is infected, yields begin to drop and the tree weakens as the disease progresses.  Eventually, the weakened tree may succumb to other diseases and die.  It must then be removed or is sometimes abandoned.  Since its appearance in Florida, the number acres of bearing orange trees has dropped from 491 thousand in 2005 to 429 thousand in 2012.  While other factors have contributed to this declining acreage (e.g. urbanization, freezes), citrus greening has played a significant role in reducing acreage and production.  In 2005, Florida produced 147.7 million boxes of oranges; in 2012, production was only 133.6 million boxes (USDA).  In addition to reducing yields and production, citrus greening has raised production costs, as farmers try new management strategies in an attempt to control the disease and the other diseases that take advantage of weakened, infected trees in an effort to extend the useful productive life of the tree. 

In 2009, the Florida Department of Citrus asked the National Academies of Science to assist in developing a strategic plan to combat citrus greening and keep the Florida citrus industry competitive.  One of the Academies’ recommendations was to form a single organization to oversee and coordinate research and development, resulting in the formation of the Citrus Research and Development Foundation, a nonprofit corporation (CRDF).  Florida citrus growers are directing the check-off funds designated for research to the Foundation’s work and have redirected some of their marketing funds to this effort.  Currently, Florida citrus growers are contributing over $4 million per year.  The Foundation is also receiving support from juice processors.  Congress has also pledged $25 million a year through 2018 to support research addressing citrus greening (Agri-Pulse).  The Foundation is working with a global network of scientist to develop a solution to this disease problem.  

The citrus greening disease is possibly an example of the types of disease problems we will face in the future that enter the United States and other countries as invasive species.  It could happen to plants or animals.  The soybean rust problem that spread through the Southeastern United States a few years ago was a similar incident.  However, we had an effective treatment (fungicide) available.  Careful monitoring and treatment of this disease has helped reduce its spread.  Future diseases may have no cure or treatment. 

The Citrus Research and Development Foundation may also be a good model for addressing future disease problems.  A single organization that coordinates research and development in partnership with producers, processors, and government bodies, including colleges of agriculture and experiment stations, may be more effective at marshaling the required resources and coordinating strategic research efforts.  CRDF was the first research foundation ever formed to address an agricultural disease.  In some ways, CRDF is similar in operation to some of the foundations leading health research efforts.  More of these kinds of efforts may be needed to address future disease problems facing agriculture.  For some industries, it may be a matter of maintaining their viability in the future. 



Agri-Pulse.  “U.S. Citrus Growers Seek to Turn the Tide on Greening Invasion.”  Agri-Pulse Newsletter, January 7, 2015, pp. 5-6. 

Citrus Research and Development Foundation, Inc.  About.  (Accessed January 19, 2015): http://citrusrdf.org/about 

University of Florida, IFAS Extension.  Citrus Greening (Huanglongbing).  (Accessed January 19, 2015):  http://www.crec.ifas.ufl.edu/extension/greening/index.shtml. 

U.S. Department of Agriculture, National Agricultural Statistical Service.  Florida Agriculture Statistical Bulletin 2014.  (Accessed: January 19, 2015): http://www.nass.usda.gov/Statistics_by_State/Florida/Publications/Annual_Statistical_Bulletin/fasb14p.htm


Dr. Paul Patterson is Associate Dean for Instruction for the College of Agriculture and Professor of Agricultural Economics.