A newly released report from the Farm Journal Foundation (the farmer-centered, non-profit, nonpartisan organization created by Farm Journal, which owns The Packer) details the top 16 most significant pest and disease issues that U.S. growers face. Citrus greening, also known as huanglongbing (HLB), is prominently featured among the “Current Threats.”
HLB was first confirmed in the U.S. in 2005 in Miami-Dade County, Fla. The disease is caused by the Candidatus Liberibacter asiaticus bacterium, which the Asian citrus psyllid vectors. The psyllid was first found in the U.S. in 1998, setting the stage for the outbreak.
In the two decades since the disease arrived in the Sunshine State, orange production has dropped from 244 million 90-pound boxes in 1998 to a projected 12 million boxes for the 2024-25 season — a nearly 95% reduction.
Citrus greening has since spread to Louisiana, South Carolina, Georgia, Texas, Alabama, Mississippi, Arizona and California.
Florida growers have battled compounding issues like devastating hurricanes, which could move the psyllid further along in the state. Hurricane Wilma (October 2005) caused $180 million in damage; Hurricane Irma (2017) caused nearly $760 million; Hurricane Ian (September 2022) hit 375,000 acres and caused about $675 million; and Hurricane Milton impacted 166,000 acres and caused about $55 million in damage.
The Farm Journal Foundation’s “Mean 16” list calls for greater public investment in agriculture research and development. (Read the full report here.)
No Silver Bullet
The report notes that many of the crop pests on the list lack full and effective treatments. Researchers across the globe and country seek to provide both short- and long-term solutions to this devastating disease.
Tripti Vashisth, associate professor of horticultural sciences and citrus extension specialist with the University of Florida’s Institute of Food and Agricultural Sciences (UF/IFAS), says growers must manage irrigation, nutrition, plant-growth regulators, psyllid control and antibiotic injections for trees infected with citrus greening.
“For the growers, it becomes really challenging that they have to be on top of each of these things, because once the tree has an infection, it is not as forgiving as a healthy tree,” she says. “If you miss fertilization on a healthy tree, it’s way more forgiving, because it has the reserves to run on ... but when it is sick, it needs everything all the time. It has become cumbersome for the growers, and that’s their biggest challenge — that there is no silver bullet and there are many different things that they can do.”
Citrus greening-induced fruit drop is also problematic. Vashisth says prior to developing management strategies, growers could lose 40% to 50% of their crop due to fruit drop.
“After that research, now we have better tools for controlling fruit drop, and it is quite successful,” she continues. “There are two plant growth regulators that we can use to control fruit drop, and it works. The timing is the critical part of it.”
Megan Dewdney, associate professor of plant pathology and Extension specialist with UF/IFAS, says growers have a profound “mindset change” to manage the disease.
“They also had to sort of get their heads around going from that very gentle method of plant management to a much more aggressive, and that’s a very much a mindset change,” she says. “We’re talking about at the same time as a biological problem; we’re also talking about almost a sociological issue.”
Dewdney, who has been with UF/IFAS since 2008, says that while it looked like a rapid expansion across the state, she thinks it was likely a slower progression.
“One of the huge challenges with this disease is the fact that it is within the vascular system, but the fact that it can kind of hide there for a long time in an older, healthy tree,” she says. “So, a tree can look relatively healthy for three, four, five years before it starts to really succumb. And that whole time, if you’ve got psyllids around, they’re able to feed on it and potentially pick up the pathogen and move it along. And so, it’s sort of sitting there silently.”
While short-term management is crucial for survival, the long-term solution lies in research and development, a priority reinforced by the “Mean 16” report.
Manjul Dutt, assistant professor of horticultural sciences with a focus on citrus and subtropical fruit breeding and genetics at UF/IFAS, says that thanks to modern technology fruit breeding — which used to be a 20-year process — is now closer to 10. And his main focus for the future of the industry is to develop HLB-resistant and -tolerant rootstock and varieties.
“Genetic resistance or genetic tolerance to HLB and other diseases remains the only long-term solution,” he says. “We need all those strategies to ensure that the grower is able to have a profitable crop in the short term, but the bottom line is you need to have tolerance and, if you get very lucky, resistance.”
To learn more about the University of Florida’s work on citrus greening, read “How Florida Citrus is Fighting Back Against Greening Disease.”
