In 1965, while on assignment for the magazine, John McPhee visited the University of Florida’s venerable Citrus Experiment Station, where the staff spent much of its time counselling citrus growers suffering from bad luck, waterlogged soil, or one of a host of pests and diseases: exocortis, psorosis, rust mites, red mites, six-spotted mites, mealy bugs. One of the worst citrus afflictions was spreading decline, caused by a nematode that feeds on tree roots. “When people in Florida are feeling depressed and miserable with some unspecific malady, they sometimes tell one another that they have the spreading decline,” McPhee wrote.
Almost fifty years later, citrus growers are contending with a malady that is both more specific and more severe—and the counsel is far less comforting.
In 2005, Experiment Station researchers were unnerved to learn that a bacterial disease called citrus greening had arrived in Florida citrus groves. Citrus greening, also called huanglongbing or yellow dragon disease, is carried by an insect called the Asian citrus psyllid. It cannot, as yet, be cured; while infected trees may not show symptoms for months or years, they eventually begin to produce yellow foliage and misshapen, bitter fruit that drops prematurely to the ground. Researchers consider greening a mortal threat: it is so damaging to fruit crops that in 2003, the U.S. classified the bacteria that causes it as a bioterror tool.
Greening, thought to have originated in Africa or South Asia, has been identified in more than forty countries—including Brazil, Florida’s main rival in the global orange-juice business. But the 2005 Florida cases were greening’s first appearance in the United States. “We had to put everything else in the freezer, quite literally,” Michael Rogers, an entomologist at the Experiment Station who had been planning to research Australian mites, said. “All our funding and all our attention suddenly went to greening.”
Eight years on, citrus researchers have few answers. The bacteria that causes greening in Florida, Candidatus Liberibacter asiaticus, has never been successfully grown in a lab, so researchers can’t examine it closely enough to learn its vulnerabilities. Introductions of Asian wasps that prey on the psyllid have so far been of limited use, and antibiotic and heat treatments are still in the experimental stage.
For now, Rogers and others advise growers to monitor their groves, immediately remove any infected trees, and apply pesticides repeatedly and aggressively. Pesticides are a familiar weapon in Florida citrus groves: when McPhee visited, he saw crews battling pests with “a liquid arsenal ranging from a fine mist of petroleum to parathion, a deadly nerve gas developed by German scientists during the Second World War.” But in the case of citrus greening, pesticides are unreliable protection at best. Psyllids reproduce at a feverish pace, and it only takes one insect to infect a tree. Some growers, hoping to avoid the high cost of pulling up sick trees and replacing them with those grown in insect-proof facilities, have resorted to dosing infected trees with extra nutrients in hopes of prolonging their lifespan, a controversial strategy that researchers fear may contribute to the disease’s spread.
So far, greening is thought to have shrunk commercial citrus production in the state by about a third, from eight hundred and fifty thousand acres under production in 2002 to five hundred and twenty thousand today. (During the state’s real-estate collapse, some growers discouraged by the spread of greening and unable to sell their land simply abandoned their groves, leaving psyllids to multiply unchecked.) This spring, greening is being blamed for an unprecedented “fruit drop,” in which eighteen million boxes worth of oranges and grapefruit fell prematurely. Growers have hired extra pickers to try to save some of the fruit, but losses are estimated at a hundred and thirty-eight million dollars, and more are expected as Valencia oranges continue to ripen in coming weeks.
Some citrus experts predict that unless greening is contained, Florida citrus crops will be gone within five years. “Among the many diseases of citrus that have invaded or could invade Florida, greening represents the greatest threat to the industry,” a National Academy of Sciences panel wrote in 2010. And the damage won’t be limited to Florida: the disease has now been identified in California and Texas, and Arizona is watching for its first case.
Southern Gardens Citrus, which supplies not-from-concentrate Florida orange juice to major brands, is betting on genetic engineering as a long-term defense against greening, and has invested more than six million dollars in research on greening-resistant trees. “Some things are motherhood, and Florida orange juice is one of them,” the company’s president, Rick Kress, said. “We’re going to find a solution.”
Back at the Citrus Experiment Station, the entomologist Michael Rogers and his colleagues aren’t so sure. The station has dealt with all manner of fruit plagues during its ninety-six-year history, but greening is the most destructive yet. “At this point, we’re just trying to sustain the industry until we can dramatically slow down the disease,” says Rogers. He drinks three to four gallons of fresh orange juice every week, and he prefers to squeeze his own. He hopes to be able to do so for a long time to come.
Photograph by Francois Perri/REA/Redux