The End of Citrus Greening? New Product Is Offering Hope
September 19, 2023 In 2004, the USDA estimated that Florida produced 242 million boxes of all varieties of oranges. A year later that figure dropped to just under 129 million boxes and continued to decrease to 41 million boxes in 2022. While there are a number of causes for the decline, none has been more in the news than citrus greening. While multinationals and other crop protection chemical companies are searching for a solution, a new product is bringing a first step to countering citrus greening. Invaio announced the Florida Department of Agriculture & Consumer Services (FDACS) approved the first registration of the company’s Trecise technology to deliver Invaio’s ArborBiotic for the suppression of citrus greening in oranges.
David Gerrard, Head of Commercial U.S., Invaio Sciences, says, “The antimicrobials that we’re using right now do not eliminate the bacteria from the tree. They suppress it.”
That suppression may help restore an industry that has cost growers around the world billions of dollars.
Citrus greening, also called HLB (Huanglongbing – yellow dragon disease) is spread by the Asian citrus psyllid (Diaphorina citri), which carries the Liberibacter bacteria that invades a tree’s vascular system. According to USDA Animal and Plant Health Inspection Service: “Symptoms of HLB-infected trees include blotchy mottle leaves, stunted growth, reduced fruit size, premature fruit drop, corky veins, and root decline. HLB eventually causes tree death.”
According to USDA, the disease was first detected in Florida in 2005 and has spread through the state’s citrus-producing areas reducing production by 75% and more than doubling the cost of production.
In 2008, HLB was detected in Louisiana, and in 2009, the disease was detected in Georgia and South Carolina. In 2012, HLB was detected in Texas and residential areas of California. Citrus greening has also been found in many citrus producing countries around the world including Brazil, China, eastern and southern Africa, the Indian subcontinent, Mauritius, the Saudi Arabian peninsula, and southeast Asia.
Finding a Solution
As millions of dollars have been invested in researching an effective treatment, the difficulty lies in studying the Liberibacter bacteria, that causes the disease.
“It can’t be grown in a dish because the dish isn’t similar enough to the phloem environment,” says Dr. Kurt Ristroph, Assistant Professor, in Purdue University’s Department of Agricultural and Biological Engineering. To date the most effective solution has been to remove infected trees.
Invaio’s treatment, Trecise, can be used on both bearing and non-bearing trees with a scion diameter of 0.4 – 6 inches.
Unlike conventional injection treatments, the treatment uses a minimally invasive system to inoculate young trees with small amounts of active ingredient to be delivered directly into the tree’s vascular system.
“It’s not a crazy idea anymore,” Gerrard says. “It’s what people are expecting. And the reason is, we’re not eliminating the bacteria from the tree. We’re just managing it right now with the active that we have.”
Invaio’s research in bearing trees shows trials of the injection have an average yield increase of 30% compared to control after just one treatment. Yields are expected to increase further after consecutive treatments, as the tree continues to recover from the effects of HLB. In the second year of a 2-year trial, research showed an average yield increase of 115% compared to control. Treated trees also produced 22% more harvestable fruit and 19% less fruit drop, and a 5% average higher brix content (a measure of total sugars).
Arcadia, FL-based TriYield, has been using Aqua-Yield’s nanoliquid solution to treat infected trees with zinc and indole acetic acid, which resulted in less fruit drop.
“Thanks to our partnership with TriYield, our distributor in Florida, we have growers that are nearing a decade of use with our technology,” says Landon Bunderson, Chief Science Officer for Aqua-Yield. “Year in and year out those growers are using the technology to drive good fruit set, and regular healthy flushes, by improving calcium and potassium uptake as well as other nutrients like phosphorus and nitrogen.
“For fighting the infection directly, Aqua-Yield technology has been shown to improve the uptake of oxytetracycline which acts directly on the bacteria to stop its growth and spread,” he continues.
Future Treatment
The pervasiveness of the disease means treated trees will most likely be reinfected and require additional injections, the Invaio solution is expected to require regular injections.
“Even if you kill all the bacteria in a particular tree, it’s still probably standing in a grove of diseased trees where the citrus greening disease is endemic,” Ristroph says. “Even if you cure all the trees in the grove, it could still come and potentially reinfect a tree. Multiple treatments are probably necessary over years.”
Ristroph does highlight another reason it has been difficult to treat this disease.
“The disease lives deep inside these trees, so getting through all the physiological barriers to reach the site of infection with an antibiotic is a major challenge,” he says.
Ongoing Research
Research on the treatment has been ongoing since it was first discovered in 1919 in China. In August 2017, Bayer began a partnership with the Citrus Research and Development Foundation (CRDF) which brought together academic researchers and the private sector. That team was awarded a $10 million grant from USDA National Institute of Food and Ag Emergency Citrus Disease Research and Extension to fund a two-year study with an additional $5 million available for a third year.
Other research is happening in California. While the disease has yet to be found in a commercial grove in California, in 2020, Hailing Jin, a researcher at the University of California Riverside (UCR) discovered a peptide that suppresses the effects of the disease in infected trees. UCR is working with Invaio’s injection system to treat the disease.
The U.S. citrus industry is valued at more than $3.3 billion. The Emergency Citrus Disease Research and Extension Program, a division of USDA, developed a $22 million grant program for fiscal year 2023 through which approved research projects could range between $350,000 and $15 million. In fiscal year 2022, the program funded 13 different research projects.
The program funds three types of projects:
- Standard Projects (SP): These support targeted problem-solving efforts that are narrower in scope.
- Coordination Networks (CN): These facilitate greater sharing of HLB research results nationally, at the state level, and internationally.
- Coordinated Agricultural Projects (CAP): These address national-scale efforts by coordinating research and extension efforts across multi-state/multi-institutional teams.
Florida might be the epicenter for citrus greening, but it’s certainly not the only citrus producing area reeling from the disease. According to Fundecitrus (Citrus Defense Fund), a private, São Paulo, Brazil based organization, that country has seen a 56% growth of citrus greening in its main orange producing regions – parts of the Sao Paulo and Minas Gerais states – and now infects 38% of trees.
The disease was first identified in 2004 and the government issued a directive in 2008.
“According to Normative Instruction No. 53, published by the Ministry of Agriculture in October 2008, the producer must inspect and eliminate plants with greening,” according to a notice from Fundecitrus. “Inspections must be carried out at least every three months and the results sent to the State Department of Agriculture and Supply through biannual reports. Plots with an incidence of more than 28% of plants with symptoms must be completely eliminated.”
Eliminating infected trees has been one of the few solutions for limiting the diseases impact. Researchers continue to investigate new solutions and offer new approaches to battling the disease.
For its part, Syngenta suggests a two-pronged approach.
The company has been encouraging growers to alternate between soil-applied neonicotinoids and foliar applications of insecticides using different modes of action. The neonicotinoids, like Syngenta’s Platinum 75 SG insecticide, use the active ingredient thiamethoxam and should be applied every six weeks.
In addition, the company recommends implementing a root health treatment program with Ridomil Gold SL fungicide. Ridomil Gold has direct fungicidal activity against the Phytophthora root rot disease. Roots rapidly absorb the fungicide, which is then translocated throughout the root system, promoting root health and crop development.
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