Arlington, Va. — The citrus industry and the U.S. Department of Agriculture are uniting to defeat citrus greening, but victory against the bacterial disease that first appeared in Florida in 2005 is still years away.
A workshop at the USDA Agricultural Outlook Forum on Feb. 21 looked at citrus greening and the future of the citrus industry, and panelists said Huanglongbing (citrus greening or HLB) has had a rapid and destructive effect in Florida. The disease has spread to other citrus growing regions of the country, but it has not had as devastating an effect on other areas.
While some believe the Florida citrus industry could be in serious peril of collapse within a few years because of HLB, researchers said finding genetically modified citrus trees immune to the disease could take a decade before commercialization.
Citrus greening was first identified Florida in August 2005, said Ed Stover, researcher with USDA Agricultural Research Service, and up to 70% of the state’s citrus trees are now infected. Within a few years of infection, many citrus trees become weak, have poor quality fruit, and heavy fruit drop, he said. Eventually infected trees may die or become useless, Stover said.
Florida’s citrus output has dropped from about 30 million field boxes in 2000 to about 15 million boxes in 2013-14, he said.
“It is getting worse all the time,” he said.
While there was optimism a few years ago that nutritional solutions could provide an answer, that optimism is slipping away, he said.
Some reports indicate up to 40% of the Florida citrus crop dropped from trees before harvest last season. Yield losses pinned on citrus greening in Florida have been pegged at $300 million annually. Growers are spending $500 per acre to fight citrus pests, said Prakash Hebbar, with the Citrus Health Response Program with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service,
Panelists said the solution to citrus greening — spread by the Asian citrus psyllid — could involve either genetically modified insects or genetically modified citrus trees, researchers said, but other short- and medium-term solutions also are being pursued.
“I think there will be a series of solutions that will evolve over time,” Stover said. “In terms of transgenics there is a group of trees that have two different spinach genes produced by Erik Mirkov of Texas A&M University that are out in field trials that are reported to have significant levels of resistance,” Stover said.
It could take ten years or so for that solution be available to growers, he said.
If the modified variety is indeed the answer, Stover said it will time to approve the trees by federal regulators and the limited amount of resistant trees will take time to propagate, he said. “It is a fairly slow process to go from having a dozen trees to having enough bud wood for 500,000 acres.”
The workshop did highlight the heavy investment by industry and government to fight the disease.
“We cannot manage or control this disease without a team effort,” said Marylou Polek, vice president of science and technology for the Citrus Research Board, Visalia, Calif.
Chavonda Jacobs-Young, associate administrator for national programs of the USDA’s Agricultural Research Service, said the farm bill authorized $25 million per year through 2018 for the Emergency Citrus Disease Research and Extension Program.
Prakash Hebbar, with the Citrus Health Response Program with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, described the Citrus Health Response Program, a public-private partnership between the agency, university researchers, state departments of agriculture and industry scientists.
Hebbar said medium-term strategies from APHIS include epidemiological studies that will help develop models that can determine or predict the incursion and spread of HLB and other diseases. APHIS has also established public and/or private sector partnership to develop biological control technologies for the Asian citrus psyllid, he said.
Long term, Hebbar said researchers are looking to develop resistant/tolerant citrus trees, maintain bearing citrus trees even if they are infected with HLB, early detection methods for the citrus greening disease and methods to trace infectious psyllid populations and limit encroachment into citrus production areas.
Polek said researchers are trying to release parasitic wasps inside field tents in citrus groves.
However, Polek said the wasps have been attacked by Argentine ant populations because the ants try will protect the psyllids because they feed on their sticky secretions.
The spread of the Asian citrus psyllid could threaten organic farms, and researchers have a dilemma about how to devise treatment programs for both conventional and organic growers. Polek said chemical treatments in urban areas isn’t sustainable, so the wasps will be used.
For now, Stover said Florida citrus growers are pretty much committed to living with the disease. Growers are looking for new ways to combat psyllids and develop resistant trees, he said.
California has psyllids in Los Angeles and other areas of Southern California, but not in major citrus areas. Only one HLB-infected tree has been detected so far. The focus in California is psyllid-monitoring and management, communicating with citizens, and diagnostics for early detection. Stover said Texas has widespread psyllids but only three groves have HLB. Texas has similar goals as California in psyllid biocontrol in residential areas. Arizona had a few psyllid finds that were controlled, Stover said.