I have written about Citrus Greening a number of times on this blog. With it being the most serious of Citrus diseases out there, the Citrus Guy would be totally remiss in not bringing it to your attention. Well, there have been some updates, both good and bad.
Let me bring you up to date very quickly on this disease in case you haven't heard about it.
Citrus Greening, also called Huanglongbing or yellow dragon disease, is a very serious disease of citrus. This bacterial disease is thought to have originated in China in the early 1900s. There are three strains of the bacteria, an Asian, an African version, and a Brazilian.
The Asian strain, Candidatus Liberibacter asiaticus was found in Florida in early September, 2005.
The most characteristic foliage symptoms of Citrus Greening are the blotchy mottling of leaves and leaf yellowing that may appear on a single shoot or branch. The disease may also cause small, narrow leaves and short stems that give plant growth a bunched appearance. Other symptoms include twig dieback, poor flowering, and stunted growth. Fruit from diseased trees is small and often misshapen. Typically, some green color remains even on ripe fruit. Affected fruit tastes bitter, medicinal, and sour. Seeds usually abort, and fruit set is poor. The tree may survive for several years, but death is inevitable.
The disease has been found in two parishes in Louisiana, and in two counties in South Carolina. The entire states of Georgia and Florida are under quarantine. There are also a number of Mexican states listed. The list of quarantines for the Asian Citrus Psyllid, the transmitter of the disease, seems to be getting longer every day. It includes: Alabama, Arizona, California, American Samoa, the Northern Mariana Islands, Florida, Georgia, Guam, Hawaii, Louisiana, Mississippi, Puerto Rico, South Carolina, Texas....Got the point? This thing is spreading.
On April 21, 2010, the Animal and Plant Health Inspection Service (APHIS) confirmed the first detection of citrus greening, in plant tissue samples collected from Key Lime trees located at a local agricultural experiment station near St. Croix, U.S. Virgin Islands. In addition, plant tissue samples of Key Lime from nearby residential properties also tested positive for the disease. Based on recent surveys, the insect vector responsible for transmitting this disease, Asian Citrus Psyllid, is also present.
Okay, had enough bad news? Here is some good news.
A team of scientists from the Agricultural Research Service and the University of Florida’s Indian River Research and Education Center have turned an ornamental plant into a tool for combating this bacterial disease.
Periwinkle, (Catharanthus roseus), has proved to be an effective screening tool or treatments to control Huanglongbing, according to Yong-Ping Duan of the ARS, U.S. Horticultural Research Laboratory in Fort Pierce, Fla.
Duan and his colleagues have found that periwinkle performs well as a stand-in for citrus, becoming quickly infected with HLB bacterium, and responding well to antibiotic compounds tested to reduce infection. The researchers used HLB-infected lemon trees to infect periwinkle plants and then ran greenhouse experiments to find the optimal nutrient and soil treatments for regenerating periwinkle with high infection rates.
Duan emphasized that the results are limited to greenhouse settings and that the chemical compounds, must still be evaluated in field trials and approved for use by regulatory agencies before commercial use is possible.
Untold millions of dollars are being spent on finding ways to combat this disease. There are more than 130 projects and studies going on, according to Peter McClure of Evans Properties and the 2009 Citrus Achievement Award winner.
One of these studies that is going on, basically, will develop a vaccine that we can give to a sick Citrus tree so that it will produce antibacterial compounds to protect itself.
As a hobby Citrus grower and lecturer, I find this very exciting. We can put people on the moon, make huge pieces of metal fly and float, but we can't make a sick Lemon tree well?! Hopefully soon this disease will be just a footnote in the history of citriculture!