Citrus Greening Ravages Production
It sounds like the premise of a bad science fiction movie (or maybe a pretty good one in the hands of, say, Ridley Scott). A tiny invader produces a deadly poison that leads a species to the brink of extinction. But that’s exactly what could happen to the citrus industry right here in Florida if efforts to control citrus greening aren’t successful.
Researchers at the University of Florida’s (UF) Institute of Food and Agricultural Sciences (IFAS) say that the Sunshine State ― a place long identified and branded by its oranges―has lost approximately 100,000 acres and $3.6 billion in revenue to the ravages of huanglongbing (HLB), or citrus greening, since 2007. The result: today (Dec. 9) the USDA forecast was revised down further to 69 million boxes of oranges in 2015 ― the lowest since 1964 and a big drop from July estimates for 96.7 million boxes. Earlier 2015 forecasts predicted upwards of 102 million boxes.
The culprit is the Asian citrus psyllid (ACP), an insect native to Southern Asia which feeds on leaf sap and creates Candidatus Liberibacter asiaticus (CLas), a bacterium that starves citrus trees of nutrients. Infected trees produce fruit so green and misshapen as to be unsuitable for sale or juicing. Most trees eventually die.
Time is short if citrus is to rebound, according to Florida Commissioner of Agriculture Adam Putnam. “This industry is too important to our state and too important to our nation to let it slip away,” he said at a hearing with the Florida Senate Agriculture Committee and citrus growers at Sebring in November.
Control Strategies
To try and keep citrus yields from dropping further, the nonprofit Citrus Research and Development Foundation (CRDF) was created in 2009 as a Direct Service Organization of UF. It has an annual budget of $14 million to $18 million to fund a research portfolio of 105 projects, including those for field testing and delivering HLB solutions to growers.
Dr. Harold Browning, chief operating officer of CRDF, says that several methods are being explored to control citrus greening. These include pesticides targeting ACP to slow the spread of disease to uninfected trees, biological control, and attractants and repellants such as reflective metallized mulches under new plantings.
“We’re also targeting the CLas bacterium itself by testing thermal and chemical means by which infected plants can resume normal growth and production,” said Browning. The Environmental Protection Agency is close to approving three products designed to combat CLas. Once given the green light, growers could be using them in 2016.
The CRDF’s other strategy for HLB intervention takes place at the plant level. Research has uncovered best methods for irrigating and feeding plants before or after becoming infected. Growth regulators and other treatments have also been applied to help trees produce and retain fruit, and plant breeding teams are producing and releasing new HLB-tolerant rootstocks.
In addition to CRDF’s work, researchers with UF’s IFAS have developed genetically modified citrus trees. They’ve demonstrated enhanced resistance to greening and the potential to resist canker and black spot. However, commercial availability of these trees is still several years off.
According to Browning, each approach to combat HLB has shown some benefit. “Progress is being made.”
A Long Road Back
As noted in an article earlier this year in The Atlantic, control efforts are costly. A grower must now spend up to $2,250 an acre to grow trees whereas prior to greening it was $850 an acre, according to industry association Florida Citrus Mutual. Some growers, particularly the smaller operations, have already quit trying. USDA estimates there were 126,000 acres of abandoned groves in Florida in 2014 and 7,300 acres of forested areas with abandoned citrus. This only makes the problem worse, as ACPs migrate from abandoned groves to healthy ones nearby.
“We’re way past losing hobby growers at this point,” said Putnam at November’s Florida Senate Agriculture Committee meeting in Sebring. “(…HLB) is impacting the heart of the industry.”
If efforts to control or eliminate HLB are successful, it may be awhile before the industry can rebound to near pre-disease levels.
“Gradual adoption of solutions that prolong or preserve tree health have an immediate impact,” said Browning. “But rehabilitation of mildly to moderately injured trees could take several seasons and the more chronically declining trees may be beyond saving.” Replanting groves with HLB-resistant trees is time consuming, with 5 to 8 years needed before the new plantings reach full fruit production.
Successful management of HLB is vital to the survival of a $10.7 billion industry. The long-term stability and future of Florida citrus will depend on further reduction of ACP insect populations, preservation of healthy trees and ongoing development of disease-resistant plant stock. The big battle against a tiny invader and the killer poison it leaves behind rages on.
Photo Credit: Top image by T.R. Gottwald and S.M. Garnsey / USDA Agricultural Research Service.