In the past 12 years, one pest has single-handedly tripled production costs and cut yields by 25% for the Florida citrus industry.
Huanglongbing (HLB), also known as citrus greening, is a disease complex that uses the citrus tree as the host. Candidatus Liberibacter asiaticus is the specific bacterial pathogen, and the vector is the Asian citrus psyllid. HLB was first found in Florida in 2005. The first trees found infected with HLB were just west of Miami. That left most in the industry to conclude the disease came through the Port of Miami. The new disease showed up in the midst of another challenging battle that was underway.
“In 2005, our industry was in the middle of battling canker,” explains Andrew Meadows, communications director at Florida Citrus Mutual. “When greening showed up, it was like a guy was stealing third while another player was stealing second.”
HLB destroyed China’s citrus production more than 100 years ago. Before coming to the U.S., it had started to cause dramatic declines in Brazil’s citrus industry. The psyllid had been found in Florida since 1998.
“It’s a lesson in never being comfortable with where you are, and you’ve always got to be on the lookout for potential threats,” says Mike Roberts, division manager of Griffin Fertilizer, Frostproof, Fla. The company is part of Ben Hill Griffin Inc., and serves all areas of citrus production across the state.
“Some employees and customers headed to Brazil immediately to learn as much as they could. But from where we started with this, no one understood the potential,” Roberts explains. “There’s a latency period from infection to symptoms, so it was much further down the road than we suspected at first. It had probably been here longer than we thought and spread further than we knew.”
The University of Florida released a study estimating that $900 million annually was lost due to HLB from 2006 to 2012. And in those five years, growers lost an estimated $1.66 billion. Meadows, with Florida Citrus Mutual, says those numbers have likely doubled since 2012.
“It’s devastating,” says Brent Sutton, president of Growers Fertilizer in Lake Alfred, Fla. “Every grove has it, and production is 25% of what it used to be. Since we’ve gotten greening, what used to be a check has turned into a bill.”
All Hands On Deck. There is no known cure for HLB-infected trees.
“We are working with a population of trees that is nearly 100% damaged or infected by the pathogen,” says Jim Graham, a retired soil science professor at the University of Florida, who spent the last 10 years of his career researching HLB at the Citrus Research and Education Center.
In 2016, the University of Florida reported orange acreage was down 26%, and total yields had decreased by 42% since HLB was first identified in the state. To combat the disease, grower organizations have put more than $100 million toward research, and $150 million has either been spent or appropriated by the state.
“The infection is variable in a field and across fields,” explains Kate Donaleshen, a researcher with Alltech. “Right now, it’s assumed if a tree is moved outside of a greenhouse, it will get infected.”
Changes To Business. “Every bit of our citrus selling is related to HLB,” Roberts says. “Effectively every acre is infected, so all decisions–fertility, pest control–all of it has to do with managing HLB.”
The initial approaches in fighting HLB were scouting and spraying for the psyllid and also removing infected trees. Still in place are Citrus Health Management Areas (CHMA), which are voluntary programs to scout, manage and spray for the Asian citrus psyllid. The CHMA consists of a group of neighboring growers that coordinate applications to minimize movement of the psyllid.
At the peak of using psyllid sprays as the main tactic, application costs per acre often exceeded $2,000.
In recent years, the strategy has changed. Once infected, the bacteria attacks the tree’s phloem, which is responsible for distributing all energy in the tree. The hypothesis is that if a tree can be maintained as healthy as possible below and above ground, then it’ll have a better chance of fighting off greening. There are no known resistant varieties.
At Growers Fertilizer, Sutton estimates that production costs have risen threefold. “A lot of things have changed in how we grow citrus, and in turn, we are trying a lot of things to stay productive,” Sutton says. “More so than ever before, if a grower isn’t spraying and fertilizing properly, the tree is going to die.”
In the enhanced nutritional management strategy, growers no longer pursue an aggressive tree removal program. They still attempt to reduce psyllid populations, but the focus is placed on a foliar nutritional program in an attempt to mask the symptoms of the disease. The University of Florida’s Institute of Food and Agricultural Sciences estimates that this approach increases grove maintenance costs by $200 to $600 per acre per year.
“It’s all about getting as much life out of the tree as we can,” Roberts says. “For young trees, we used to make applications every six weeks, and now we may be in the grove applying insecticides for psyllids every three weeks–just trying to keep the tree healthy and get it to the fruit-bearing age. If the tree gets stunted early, it’ll never support a crop.”
Multiple Therapies. Additionally, a lot of focus has been directed to the quality of water used to irrigate trees.
“Over a period of three seasons, we were able to see a reduction in the impact of high bicarbonates in the irrigation water on HLB-damaged root systems with acidification treatments that dropped soil pH from 6.5 to 6.0. Importantly, this soil pH adjustment increased uptake of calcium, magnesium, zinc, manganese and iron,” Graham says.
He explains that HLB damages the fibrous roots in infected trees. Initially, root density declines by 30% to 50%, so much of his research has focused on root health. As Graham explains, researchers and growers have been learning on the fly about managing root health for this disease.
“There have been some novel approaches to fighting greening,” Graham says. “For example, there are recent studies of the benefits of different types of artificial and green mulches installed around newly planted trees. There have been multiple antibacterial therapies applied as sprays and soil drenches, including thermal heating of the tree’s canopy. Reduction of water and nutrient stresses has produced positive recovery of declining trees.”
Roberts says his agronomy team is looking at everything.
“We take one step forward and two steps back. Greening is a worthy opponent,” Roberts explains. “We’re trying multiple fertilizer applications, including multiple dry applications, injections and foliar feedings. The idea is a constant feed of plant nutrients so the tree wants for nothing. And we work to stay focused on sound agronomy.”
Water timings have been adjusted, and microsprinklers may be irrigating every other day–up from two times a week.
Focus On The Long Game. One challenge with the production changes is the nature of the crop–oranges are perennials. Trees aren’t expected to yield fruit for five years.
“The changes we make today may not manifest themselves for a whole year,” Roberts says. “We’re trying to support the tree but not break the bank. We’re keeping these trees alive but losing the production game.”
That’s the game plan retailers are implementing with growers today–keep the trees in production for as long as possible.
“The resilience of the Florida grower is tremendous today,” says Steve Olson, product manager with Bayer. “Those who have the resources and are committed to sustaining production have been somewhat successful. They know they are fighting to be sustainable long term and continually sharpen their pencil to make it work for their operations.”
Moving Forward. Farmers and retailers continue to battle greening, without a clear end to the war.
“We have a way to go, but they have found root stocks more tolerant and resilient to greening. However, it will take time to propagate, grow and plant replacement trees,” Graham says.
Industry stakeholders are eager to see emerging technologies applied to solve HLB, such as RNA interference or gene editing, such as CRISPR.
“The holy grail will be at some point to block the vectors’ transmission of the bacterium into the tree,” Graham says.
To be more than a cautionary tale, members of the Florida citrus industry want to share their stories to help other agricultural industries avoid facing this kind of setback.
“The California and Florida industries are working together to help California citrus growers apply the lessons learned in the Florida,” says Bayer’s Olson. “One key lesson is that growers, retailers, University Extension and all stakeholders collaborate and work together. When they find an invasive species or new pest they need to be ready to act quickly.”