The Silent Struggle of the Citrus Industry
Throughout the world, there are a number of afflictions that can plague plants of all shapes and sizes. As time continues to pass, plants continue to change. Each change will often lead to an evolution that will potentially combat their native threats. But, there is one plant family that seems to be increasingly in danger with each passing year, that time and evolution can’t protect.
The citrus family.
Last month we took a deep dive into what makes the two most powerful citrus states in the U.S. move. Now, we’re going to take you into the constant struggles these states face, as they combat a disease that has almost all but wiped out the global citrus supply.
This month, we’ll be talking about Huanglongbing (HLB), also known as Citrus Greening Disease. This disease has been responsible for compromising every citrus species throughout the globe. With an immense workforce behind the industry, it wouldn’t just be our countertops that could be left empty if the fruits simply disappeared, but also the stomachs and wallets of the millions of people it employs.
So, What is Citrus Greening?
Citrus Greening Disease, or Huanglongbing (HLB), is a far-reaching citrus disease that has impacted the entire world of citrus growing. Once a tree has contracted the disease, its fruit will appear misshapen and green, while having a bitter taste. Within a few years of the disease infecting the tree, it will die.
The name Huanglongbing means “yellow dragon” and pays tribute to the yellow offshoots that the tree will develop as a response to the disease. The name also recognizes the yellowing and greening effects that the disease will have on the fruits.
While the disease is not contagious to human beings, the threat that this disease presents is a threat to the citrus family itself. It is currently identified that Citrus Greening has the capacity to infect every type of citrus on the planet.
The disease is believed to have first emerged in 1919 in the Southern part of China. [1] From there the disease will continue to spread all the way to the United States by 2005 when it is first identified in Florida.
Since its arrival, “citrus greening has been responsible for a 90% reduction to the production of Florida’s most valuable crop” [4].
The active bacterium that infects the citrus plant is the Candidatus Liberibacter asiaticus (Las). Through the Asian citrus psyllid (Diaphorina citri), the bacterium is spread infecting citrus plants or contracting the disease themselves.
Once the psyllid has contracted the bacterium for the disease from an infected tree, it will then infect healthy trees with the disease-causing their decline and the spread of Citrus Greening.
With few treatments available for the disease and no proven cure, conversations that surround Citrus Greening often focus on slowing the disease, and the extent of the damage that it has caused.
Measuring the Impact of the Disease
The impact that the disease has had on citrus trees has been overwhelming and dismal. In 2016, the USDA National Institute of Food and Agriculture released a Fact Sheet that recognizes that as a direct result of Citrus Greening, we could see the destruction of the citrus industry within our lifetime.
Most severely hit, is perhaps the citrus state of Florida where they’ve seen a decrease in orange trees by 20 million, since 1966. In addition to oranges, the grapefruit trees have also drastically declined, to roughly a third of the 14 million that they used to be.
With a recognized impact of serious proportions, the USDA and citrus community fear that the devastation the disease can cause to California, would be just as grave.
California produces 80% of citrus fruits sold throughout the United States.
In response to the seriousness of Citrus Greening, regulatory efforts surrounding the citrus communities have amplified in hopes of slowing down the spread, and prolonging protection against it for those who have yet to be exposed.
The states that have confirmed Citrus Greening are: California, Florida, Georgia, Louisiana, Puerto Rico, South Carolina, Texas, and the U.S. Virgin Islands.
The states that have confirmed the presence of the psyllid are: Alabama, American Samoa, Arizona, California, Florida, Georgia, Guam, Hawaii, Louisiana, Mississippi, Northern Mariana Islands, Puerto Rico, South Carolina, Texas, and the U.S. Virgin islands. [3]
So far the types of citrus that are identified to be at risk from the disease are: Chinese box-orange, Curry leaf, Finger-lime, Grapefruit, Key Lime, Kumquat, Lemon, Lime, Limeberry, Mandarin Orange, Mock Orange, Orange, Orange Jasmine, Pomelo, Sour Orange, Sweet Orange, Tangerine, and Trifoliate Orange.
But…Not All Hope Is Lost
With the disease continuing to spread and ravage the industry, citrus giants are beginning to see signs of hope through developments against the disease that could just possibly save their entire way of life.
While we previously mentioned that there is no known cure for the disease, we couldn’t bring anything to your attention, at this time, that didn’t come alongside a hopeful ending.
So, here’s the good news:
Researchers around the country have been working non-stop for years to examine every possible avenue that can expedite the discovery, management, and treatment methods for Citrus Greening.
At the University of Florida (UF) researchers have discovered that citrus trees grown “under oak canopies or alongside Oak (Quercus) trees, are healthy” [4]. Whereas the citrus that is grown a few rows away from this structure often show signs of HLB.
This observation led to further interest from scientists and researchers that brought them to identify the affect that Oak (Quercus) leaf extracts have as a combatant against the bacterium Candidatus Liberibacter asiaticus. Their findings identified that the leaf extracts from the Oak (Quercus) restored the leaves of the HLB infected citrus trees within their physiological parameters. This new discovery could quite possibly mean effective methods against the disease and perhaps greater longevity for the infected trees.
But, these discoveries and advancements haven’t come without a cost, and their own shortcomings. In August of 2019, the UF published an article that back pedaled the long believed “silver bullet” approach of antibiotic spray to fight against HLB.
They acknowledged that the practice of spraying oxytetracycline and streptomycin solutions may not be as effective as originally believed in combating HLB. But, what they did find was that trunk injections of the bactericides resulted in access to the cellular structure of the trees and their fruit that allowed the oxytetracycline to effectively combat the HLB.
But this isn’t all of the good news, finally, as we close out our article, we have one more amazing development against this deadly citrus disease. The first effective treatment, capable of controlling Citrus Greening.
On the west coast, in Riverside California, University of California at Riverside (UC Riverside) has developed the first ever treatment method with curative properties through the use of antimicrobial peptides.[5]
The peptides derive from a molecule extracted from the Australian Finger Lime. Through 2 years of grueling research Dr. Hailing Jin was able to identify the relationships between the citrus variety’s resistance to the disease and combative properties needed to be successful in other citrus varieties.
Through the project’s successful trialing and development, UC Riverside has entered an exclusive, global licensing agreement to bring this treatment to market with the company, Invaio. The peptide treatments are needed a few times throughout the year, providing a cheaper and more effective solution in combating HLB than any other approach in the industry.
Looking to the Future
While developments continue, and there are no guarantees of success, it is important to acknowledge how this disease came to be so difficult. While there were a number of variables that couldn’t have been controlled, there were a number of variables that could have.
The important takeaway from this disease is that while the challenges have been great, our efforts make a difference both in prevention and in treatment.
As a plant lover, grower, protector, or admirer, it is our responsibility to ensure that our plants are being protected, and are protecting other plants.
When purchasing plants, be sure to ask what treatments your plant may have received before purchasing. Check to see if the plant is an invasive species to your region. And ALWAYS keep a watchful eye for signs of pests and disease.
Diseases like HLB aren’t just won and lost in a single battle in contributing to its spread. The war is won through continuous combined efforts of regulatory compliance, and company’s like Plant Sentry stepping up to do the right thing.
We’re always looking for new friends willing to do the right things for growers, consumers, and ultimately themselves. If you think you know one, or may be one of them, be sure to reach out to us below and tell us more about yourself!
Citations:
[1] Bové, J. (2006). HUANGLONGBING: A DESTRUCTIVE, NEWLY-EMERGING, CENTURY-OLD DISEASE OF CITRUS. Journal of Plant Pathology, 88(1), 7-37. Retrieved September 30, 2020, from http://www.jstor.org/stable/41998278
[2] Citrus Greening FAQ. (n.d.). Retrieved September 30, 2020, from https://gardeningsolutions.ifas.ufl.edu/care/pests-and-diseases/diseases/citrus-greening-faq.html
[3] Citrus Greening. (n.d.). Retrieved September 30, 2020, from https://www.aphis.usda.gov/aphis/resources/pests-diseases/hungry-pests/the-threat/citrus-greening/citrus-greening-hp
[4] Koestoyo, Posted:, 22, S., 23, J., 25, G., 22, A., . . . 18, E. (2020, February 12). Oak trees may hold antibacterial to help infected citrus trees. Retrieved October 01, 2020, from http://blogs.ifas.ufl.edu/irrec/2020/01/21/oak-trees-may-hold-antibacterial-to-help-infected-citrus-trees/
[5] New tools in the fight against lethal citrus disease. (2020, August 25). Retrieved October 02, 2020, from https://news.ucr.edu/articles/2020/08/10/new-tools-fight-against-lethal-citrus-disease