Scientists Get Creative to Come up with Manageable Solutions to Citrus Disease
There’s no cure yet for citrus greening, or Huanglongbing (HLB), but researchers are learning a lot more about managing the disease spread by the Asian psyllid.
“We really don’t have a solution as of yet. We have some great management tools,” says Dr. Jackie Burns, director of the Citrus Research and Education Center run by the University of Florida’s Institute of Food and Agricultural Services (IFAS). “That ultimate solution is still being actively sought with everything we have.”
“Things we didn’t have a clue about two years ago we’re starting to understand,” says Dr. Harold Browning, chief operating officer of the Citrus Research and Development Foundation (CRDF) in Lake Alfred. “We haven’t crossed the finish line. We just got around to the last lap and we’re in pretty good shape. I feel really good about it as a scientist.”
While no “silver bullet” is expected to end the plague, Dr. Browning says researchers are close to “manageable solutions.” They involve controlling the psyllid with chemical sprays and natural predators, boosting trees’ health with nutritional measures that will enable them to withstand infection better, developing more HLB-resistant root stalk, developing antimicrobial therapies, protecting vulnerable young trees, and adjusting pesticide-use rules to maximize effectiveness. Although treating plant vascular disease with therapy is unproven, they are making good progress, he says.
Some 500 scientists from across the globe gathered in Orlando last month to share what they are doing to eradicate HLB, a disease that has cost an estimated $4.5 billion since it was discovered in 2005, according to UF economists. They were impressed with a sense of urgency to find something to keep the Florida citrus industry alive until a cure is found.
Afterward, the mood was encouraging. Mike Sparks, executive vice president and chief executive officer of the Lakeland-based grower cooperative Florida Citrus Mutual, the conference’s host, gave the event an “A+” rating. “The breath and the depth of knowledge was there,” he says. “We really challenged the researchers.”
While U.S. citrus utilized production was down slightly for 2011-2012, Florida supplied 65 percent of the total 11.7 million tons and California supplied 32 percent, according to a Florida Citrus Statistics report released March 1 by the U.S. Department of Agriculture (USDA) National Agricultural Statistics Service. Florida production was up three percent from the previous year’s 166.1 million boxes, the report shows, while other states show a decline.
Polk County was Florida’s top producer, with 31.2 million boxes, according to the data. Highlands County was the second largest producer with nearly 23.7 million boxes. Together they accounted for more than half of citrus production statewide. Commercial citrus acreages in Florida climbed to 941,471 in 1970, but dropped to 531,493 in 2011-2012, the report shows. Polk topped the list for commercial citrus acreages, with 82,572, followed by DeSoto County with 64,258 of the state’s acres.
“We are losing too many acres to this disease. Fortunately, the recession has slowed down some of the urban encroachment,” says Dr. Calvin Arnold, horticultural research lab director for the USDA in Fort Pierce. Greening is not totally responsible for the reduced acreages. “All of that is not due to HLB and pests and diseases,” Sparks explains. “Mother nature has really not been kind to the industry for the last decade and half.”
Despite hurricanes, canker and now HLB, growers are managing. “Now is probably one of the most challenging times they’ve ever been through. But the glass is still half full,” Sparks says.
Growers believe in the research, which is why they have funded it with $60 million in private dollars in the last five years. “They know research is what’s going to get us out of this,” Sparks explains.
Scientists are attacking the HLB problem on three fronts:
• By learning more about the trees and their ability to resist the disease;
• The deadly bacteria;
• And its carrier, the psyllid.
“Long term, we know we need resistant trees, but that takes time. We’re working very hard on that,” Arnold says, referring to research at UF and Texas A&M University. The disease apparently may appear in the roots in the early stages, which explains why some treatments may not be working very well, Dr. Burns says.
If they can find the gene responsible for causing the disease, it can be repressed. Along the same line of thought, Arnold adds, “We know how to silence the genes. If we can find a gene in the citrus DNA sequence that strengthens its immune system, we can regulate that gene and make it stronger.”
“Science moves pretty slowly and it’s a methodical pursuit,” Dr. Browning explains. “The problem with that is it’s slower than people would like it to be.”
The conference encouraged innovative thinking – like putting a clear plastic cover over the trees to kill the bacteria. Think of it like a giant baggy placed over a group of trees and then moved and hydraulically lowered over another group.
“We hope some type of heat therapy might be deployed,” Arnold says. “It doesn’t require regulatory approval. That’s one of the things that excites us about it.” He says they’re trying to encourage entrepreneurs, especially those with an engineering background, to figure out how to use the plastic cover idea commercially.
The conference was a cooperative effort of CRDF, USDA, the UF’s IFAS, and Florida Citrus Mutual. A recap was presented to growers at the Lake Alfred IFAS Center earlier this month.
In spite of positive strides, growers are still playing a waiting game as fruit drops prematurely from the trees.
“It isn’t a pretty picture. Everybody is worried,” Dr. Browning says. “The industry is starting to feel the effect of the disease.”
Dr. Burns adds, “This is a very very serious time for the industry. We need a solution now. They’re working hard every day” to find one.
story by CHERYL ROGERS
psyllid photo by DAVID HALL