Ecology And Environment

Citrus Greening Disease



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Citrus Greening Disease has the US citrus industry terrified, and for good reason too. This bacterial infection threatens to obliterate entire groves of citrus, potentially wiping out the species altogether if left unchecked. Citrus Greening Disease is a bacterial disease first discovered in China in the 1800's. Since then it has been decimating citrus crops in Asia, Africa, and the Saudi Arabian Peninsula. In 2004 the disease was reported in Brazil; and, in 2005, in Florida. Although Florida is the only state so far infected with Citrus Greening Disease, the insect responsible for spreading the disease has been discovered in five other states, as well as Guam and Puerto Rico. There is no area of the world that is not fighting the onslaught of Citrus Greening Disease.



Citrus Greening Disease is also known as Huanglongbing, yellow dragon disease. It is transmitted by only one insect, the 3 millimeter long diaphorina citri - the asian citrus psyllid. This insect was first discovered in the US in 1998 in DelRay Beach, Florida. The outbreak of the disease wasn't discovered for another seven years. The asian citrus psyllid spreads the bacterium candidatus liberibacter asiaticus, by feeding on the liquid content of the citrus leaves. Once a psyllid eats from an infected plant, they carry the bacteria for life, bringing it to each plant that it subsequently feeds on. The bacteria attacks the vascular system of the citrus trees, stopping the transport of water and nutrients. The resultant is green, bitter, and inedible fruit, leaf discoloration, and yellowed shoots. After two or more years the plant completely dies. There is no cure for Citrus Greening Disease, forcing citrus farmers to cut down their infected crops.



In Florida Citrus Greening Disease has become a state wide epidemic. Once the psyllid was found in 1998, the state immediately implemented a state-wide quarantine. But due to the large number of psyllid hosts, including citrus, orange jasmine, and curry leaf plants, the populations established themselves anyway. The USDA and the state have been working together to fight the spread of the disease, doing everything they can to save the $9 billion dollar Florida citrus industry. The disease threatens to force citrus prices to soar. This alone could threaten the citrus growers, whose production costs have doubled since the arrival of the disease. Collectively they have formed the Citrus Health Response Programs, which works to set standards for regulation, oversight, and management of the disease. All of the disease host plants are quarantined by law, and all movement of potential psyllid host material is regulated. Regular surveys are conducted of citrus groves. It was in one of these targeted surveys that they discovered the first two Florida citrus trees with Citrus Greening Disease symptoms.



Once a tree is infected it is immediately cut down. Pesticides are used on commercial citrus crops as a preventative measure, although this can only save some of the plants. Researchers have been working on other ways to control and eventually to cure Citrus Greening Disease. Another partial solution is reducing the psyllid populations by introducing natural enemies into the citrus groves. The parasitic wasp tamarixia radiata has successfully had some result. Florida growers collectively invest 40% of their marketing budget into research, which comes out to $20 million dollars a year. It is due to the states diligent efforts at combating the spread of the disease that they have managed to save enough of their crops to sustain their citrus industry, but other states fear that they won't be so fortunate.



Florida grows 71% of all US citrus, mostly sold as juice. The asian citrus psyllid has been found in Texas, California, Louisiana, South Carolina and Georgia. California is the second largest grower of citrus in the US. They make up 27% of the market, primarily in fresh fruit. Also, a third of their product is sold overseas. They have been going to great lengths to protect their $1.3 billion dollar industry, regulating the Mexican border area and implementing heavy quarantines like Florida did. Other states, who don't have as much money to protect their citrus groves worry that if the disease spreads to their states, their crops will eventually be completely wiped out. Unfortunately, every area that they psyllid has been found in inevitably breaks out with Citrus Greening Disease.



This is ultimately a race against time. Researchers and scientists must find a way to combat the infecting bacteria before the outbreak spreads to an uncontrollable level. Meanwhile, the citrus industry is forced to spend millions to preserve their remaining healthy groves, and to protect new plants. With the risk of skyrocketing prices, the US citrus industry is vulnerable to collapse even before the yellow dragon disease can do its worst.



Sources:



http://www.doacs.state.fl.us/pi/chrp/images/Huanglongbing72.pdf



http://aggie-horticulture.tamu.edu/citrus/diagnostics/greening/greening.htm



http://mgonline.com/citrus_greening_disease.html



http://www.ipm.ucdavis.edu/NEWS/asiancitrus-news.html

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