Weathering the HLB Storm

Specialty crop growers might be aware of the disease sweeping through Florida’s citrus industry. Its impact has been tremendous and has tested the survival of the state’s signature crop. This year will mark the 20th anniversary of the official confirmation of citrus greening disease (also known as huanglongbing or HLB) in Florida.

In the past two decades, the state’s output of citrus plummeted by about 90%. Yet the industry survives, and growers continue the fight to overcome the disease and restore the industry to a viable status. Some say the word “resilience” has become an overused term to describe farmers, but Florida citrus growers embody its meaning in the HLB fight.

The story of Southern Gardens Citrus tells the battle that the entire industry has fought over the past 20 years. Jim Snively, vice president of grove operations for the company, has witnessed the disease’s spread and has been a leader in the search for solutions.

Snively earned AgNet Media’s Citrus Achievement Award in 2008 for his service in various advocacy organizations and his efforts to sound the alarm about the disease and the need for aggressive research to address the problem.

He comes from a fourth-generation citrus-growing family, so the profession is in his blood. He joined Southern Gardens Citrus in 2002, only a few years before HLB was confirmed in Florida. At that time, the company was growing on about 21,000 acres and had its own juice-processing facility.

Today, that figure has fallen to about 1,000 acres, and the processing facility closed in 2019. The decline in acreage is attributed to more than just HLB, including citrus canker eradication, hurricanes, freezes and a state buyout of acreage for Everglades restoration. But HLB has been the persistent pest that has kept Southern Gardens Citrus and many other farms from bouncing back and rebuilding production.

BELIEF IN SCIENCE

Despite the challenges presented by HLB, Snively is convinced the industry will find a way to beat HLB or live with it in a sustainable way. He believes the solution will be delivered through a tree that is resistant or highly tolerant to HLB.

From the very early days, Southern Gardens Citrus led the way among growers in advocating for science to address the disease. The company established its own research program and worked closely with the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) and other institutions on the problem.

“We found out we had HLB in our groves in 2005. At that time, Tim Gast was working with me at Southern Gardens,” Snively says. “He had worked in China, so he had experience with HLB. He also knew Dr. Joseph Bové, who was the leading authority on the disease. I asked Tim to build an HLB-management program for our groves. He reached out to Bové for guidance on what to do.”

Bové’s program consisted of scouting groves for HLB, removing infected trees, controlling the Asian citrus psyllid (the disease’s vector), moving nursery plants under cover and planting disease-free trees. That was the original HLB program for Southern Gardens Citrus, and it served as the general guidance for the industry in the early days of the disease.

“Our numbers started out low. We would find 1% or less infected trees. We’d take those trees out,” Snively says. “But those infection numbers kept growing. We really got moving on our program in 2006, but by 2014, we stopped looking for HLB and removing trees. We had removed almost 50% of existing trees by that time and that was on 16,000 acres.”

Psyllid control continued along with an aggressive plant nutrition program to encourage tree health. But the path of tree removal was clearly unsustainable. Snively says even if the entire industry had been removing HLB trees, the disease was too far along for tree-removal to work, particularly because symptoms often do not express themselves until months after infection.

Southern Gardens constructed its own nursery in 2007 to ensure it was planting trees free of the disease. The company discontinued nursery production several years ago, but still owns the nursery, which is now leased to the state for the increase of promising HLB-tolerant varieties like Donaldson.

Convinced that a tolerant tree is the ultimate solution to the disease, the company began to research avenues in breeding.

“We knew that conventional breeding might work, but it could take 100 years to develop a resistant tree,” he says. “That’s when we began looking at the potential of genetically modified organism (GMO) trees.”

Southern Gardens Citrus consulted with a Brazilian company called Alellyx Applied Genomics to develop a GMO tree for Florida. Snively said that research was very complicated and got very expensive, very fast. So, the company funded local research with UF/IFAS that was seeking to develop a GMO HLB-resistant rootstock.

“Mike Irey, a scientist for Southern Gardens Citrus, was leading these early research efforts. He had a relationship with the late Erik Mirkov, a plant pathologist with Texas A&M, who had been working with genetically inserting the spinach defensin protein into trees to resist citrus canker. Dr. Mirkov believed this approach could also be applied to HLB resistance. So, we contracted with him to fund this research and move it forward.

“Mike also had a good working relationship with UF/IFAS plant pathologist Bill Dawson, and they began working on the idea of delivering the spinach defensin gene into the tree via a benign form of the tristeza virus. That’s called viral vectoring, and it gets you around any stigma associated with GMOs. That research goes back as early as 2008.”

Southern Gardens views all of the private research and collaboration with institutions like UF/IFAS and Texas A&M as critical to the survival of the industry. Some of those experiments have stopped, and some continue, but they helped lay the groundwork for ongoing research. The UF/IFAS Crop Transformation Center was established a couple of years ago, and its first target is delivering an HLB-resistant tree via all the technological tools available like transgenics, and CRISPR.

NEW HOPE

Besides developing a resistant tree, there have been many different approaches aimed at keeping HLB-infected trees as healthy and productive as possible. Snively is a strong believer in providing his citrus trees with a good nutrition program, even before HLB.

Growers throughout the industry have developed their own programs to try to maintain and improve tree health, but declining yields and quality have indicated those practices can only sustain an HLB-infected tree for so long before the inevitable decline occurs.

The introduction of trunk-injection therapies in 2022 was met with much excitement, because it could help the industry hold on until a resistant tree is developed. Two formulations of oxytetracycline (OTC) were registered for use in citrus. These products kill the HLB bacteria inside the tree, which is an advancement over pumping trees up with enhanced nutrition.

Snively says he reached out to TJ BioTech, which manufactures ReMedium TI^®, to evaluate the product’s performance in improving tree health. He has injected all his trees twice now. The label allows one injection per season. The results were significant after the first injection.

“After the first injection in 2023, our yield increase on the total crop was 180%,” he says. “There was a 157% increase on our early-mid varieties and a 202% increase on Valencia. Here is the caveat: We were recovering from Hurricane Ian that had caused some fruit loss in 2022, so we would have seen an increase anyway because of the storm recovery. We had a 40% to 50% fruit loss from that storm. So, I don’t believe OTC created that kind of yield increase, but there is no question it helped because the trees looked fantastic after we made that first injection.”

Snively speculates that the OTC might have improved yields by 30% to 50%, but that’s just a hunch based on experience. He also adds that trees are in what many consider to be the sweet spot for responding to OTC therapy. The trees range from 6 to 10 years old. It is important to note that the yield increases are coming from historically low production numbers. After the first injection, juice quality was not improved. Snively says higher rates of OTC seem to have greater impacts on healthier trees.

“This season, after the second injection, I am projecting a 9% decrease in the crop. That was before Hurricane Milton, where we lost fruit in the early-mids (about 20%). Most of the projected decline is in Valencia (not related to Milton). Perhaps that is because they are an alternate-bearing variety. We’ve lost track of what is an on or off year due to HLB. So, maybe it’s an off year with Valencia. We know it is not from post-bloom fruit drop.

“But these trees look so good after the second trunk injection. There are really no visible symptoms of HLB. The leaf expansion looks like pre-HLB. Leaves are green, and the canopy is dense. I just believe that with the trees looking so good, the yield and hopefully the quality must be coming. It is going to take more than a couple of treatments to turn around 20 years of decline.”

Snively says trunk injection is hopefully the therapy the industry has been waiting for to bridge the gap between when science delivers a tree tolerant or resistant to HLB.

Sponsored Content