Should it appear in California, there might be no stopping it: citrus greening, or huanglongbing. The fearsome citrus-killing bacterium, first seen in China in the early 1900s, has spread steadily across the continents. It recently hit Brazil and is now wreaking devastation on the orchards of Florida, where some magnates worry that the $9 billion industry could become commercially defunct within several years. Now farmers and government scientists in California are scrambling as they prepare for — and hopefully deflect — a similar invasion.
The local alarm comes with good reason. Huanglongbing travels via an insect vector — the otherwise relatively harmless Asian citrus psyllid, or Diaphorina citri — and last June, this little insect appeared in Tijuana. Three months later a psyllid was found in San Diego, in an insect trap in a lemon tree near the Sweetwater Reservoir, south of Lemon Grove. Since then, hundreds have been detected near the reservoir and to the east, in Jamul, Ocotillo, El Cajon, Tecate, and Dulzura as well as Imperial County and south of the border, though the insects have all tested negative for the bacterium and the disease has not yet been seen in trees.
“But that doesn’t mean it’s not already here,” says Bob Blakely, director of industry relations with California Citrus Mutual, a trade organization.
Such uncertainty derives from the quiet nature of the disease, Blakely explains; once huanglongbing infects a tree, it lurks for a latent period of several years — often five or six — before symptoms appear. “Once you see the symptoms, the disease has usually spread all through the orchard.”
There is no cure for citrus greening, making the presence of the huanglongbing bacterium in combination with a psyllid infestation a recipe for disaster.
“So we really have no choice now but to act under the assumption that the disease is already here,” says Earl Rutz, who grows 20 acres of Valencia oranges in the Pauma Valley. “Basically, we have to control the psyllid.”
Huanglongbing spreads when an infected psyllid gnaws into the leaves or bark of a tree to feed. The insect also lays its eggs on the tree, and while the progeny of an infected psyllid will not carry the huanglongbing bacterium, the nymphs are likely to be hatched into a tree upon which the parent insect has fed; thus, the next generation picks up the bacterium. As they mature and move outward, the insects can spread the disease literally as fast as the wind blows. The first symptom to appear is an irregular yellow blotchiness that spreads over the leaves of a single branch. The discoloration moves to the trunk of the tree and advances to other limbs. The fruits develop into oblong irregular shapes and eventually turn blotchy green. They take on a taste of kerosene or turpentine, according to anecdotal reports, and an infected orchard is good for literally nothing — not even fruit juice. By the time a tree is found to be infected, adjacent trees have almost certainly been attacked as well. The only remedy for a sick tree is to uproot and burn it along with its neighbors.
Vast groves in Florida have come to such ruin. According to the Florida Department of Agriculture and Consumer Services, the Asian citrus psyllid appeared in Florida in 1998, presumably introduced from Brazil, where the insect was already well established. Symptoms of citrus greening were first seen in Brazil in 2004 and a year later in Florida, which produces 70 percent of the United States’ citrus crop. Most of the fruit is juiced. Since 2005, huanglongbing has destroyed roughly 16 percent of the state’s trees, reducing acreage from 750,000 acres to 650,000 today. Some reports have suggested that as many as 100,000 more acres could be infected.
The unfurling disaster in Florida has cast a dark shadow over California’s citrus industry, where some 4000 growers produce a quarter of the United States’ citrus crop and most of the nation’s fresh fruit. Ted Batkin, president of the Citrus Research Board, based in Tulare County, says that his organization has had to put several projects on the back burner, including development of improved irrigation and harvest techniques, fertilizing methods, and consumer-research studies, in order to focus entirely on fighting the Asian citrus psyllid and huanglongbing.
Earl Rutz, who sits on the Citrus Research Board as chair of the disease committee, calls the situation in California an “emergency” and says that the state faces two particular challenges. First, the latent period of the huanglongbing bacterium after infection makes locating the disease in its early stages impossible, though the bulk of the Citrus Research Board’s current work is aimed at early detection. One potential solution would be a sensory apparatus fixed to a robot that travels through an orchard, “sniffing” each tree for organic compounds released by the bacterium.
The second challenge is presented by the thousands of backyard citrus trees in San Diego alone that could harbor the Asian citrus psyllid. To educate residents about the importance of identifying and eliminating the insect, the Citrus Research Board has hired Nuffer Smith Tucker, a San Diego public relations firm, to conduct outreach, and a website — californiacitrusthreat.org — has been launched to portray images of the insect and infected trees to the public.
Since September, a quarantine in San Diego and Imperial counties has restricted transportation of leaves, branches, and other tree parts known to host the insect, but the concern among officials and industry reps is that people may unknowingly transport the psyllids on fruits harvested from trees in their yards. Officials with several government bodies are working to involve backyard citrus-tree owners in eradicating the pest. Steve Lyle, spokesman for the California Department of Food and Agriculture, says that approximately 327,000 flyers have been dispersed strategically through parts of Imperial and San Diego counties. State employees are also conducting door-to-door extermination work. Nearly 4000 backyard trees have been sprayed to date.
Most of the psyllids found so far have been caught in traps or vacuumed off citrus leaves near Highway 94 and Interstate 8, and inspectors are currently looking at trees one by one between San Diego and Calexico, applying insecticides to all citrus trees within 400 meters of detection sites. As of March 31, nearly 1300 insects had been discovered at 173 sites in San Diego and Imperial counties. In some cases, single trees contained hundreds of adult insects, constituting what Rutz terms “a mature infestation.”
“That means you’ve got a full life cycle and that they’re breeding,” he says.
Meanwhile, a similar eradication effort is underway in northern Baja California and Sonora, where the U.S. Department of Agriculture is assisting Mexican authorities as they place traps and spray suspect trees. A total of 280 psyllids have been found just south of the international border since last June. The United States has supplied $1.2 million to the Mexican extermination project, and on April 29 and 30 officials from Mexico’s citrus industry will meet in San Diego with United States industry stakeholders to discuss further cooperative strategies that might stop the spread of the Asian citrus psyllid. Officials have pointed out that only a collaborative effort can prevent a disaster.
According to Lyle, commercial citrus operations are expected to address their own infestation problems, but the two most effective pesticides — Merit and Tempo — pose a dilemma for farmers like Al Stehly. Stehly manages 200 acres of certified organic oranges, lemons, and grapefruit near Valley Center, and a single application of either pesticide to his trees will result in withdrawal of certified organic status by the United States Department of Agriculture.
“Maybe what this means is that we’ll no longer have organic citrus in California,” says Stehly, who plans to wait until absolutely necessary to treat his orchards.
Currently, Stehly practices “integrated pest management,” a system designed to eliminate most harmful insects, but not all.
“The idea is to knock them down and allow the beneficial insects to prey on the remainder, but citrus greening is a new one for agriculture,” he explains. “It only requires a single insect to transmit the disease, so you can’t leave 5 percent of the psyllids for other insects to eat. Just one psyllid can kill your entire orchard if it’s got the bacteria.”
Developing disease-resistant citrus varieties would be ideal, says Stehly, but not if it took genetic modification to get there.
“Again, that would mean organic farmers couldn’t use it.”
The Citrus Research Board’s Batkin says that isolating a variety of citrus naturally tolerant of the huanglongbing bacterium is a very likely possibility — but not an answer.
“The goal is not to find a tolerant variety, but to find a solution that we can apply to all the trees to save all the varieties.”
Finding a disease-resistant lime, for example, would not save the orange industry, Batkin points out.
Batkin, too, is an organic farmer, and he concedes that the Citrus Research Board and other investigators have made little to no progress in developing organic sprays effective against the Asian citrus psyllid.
Stehly says that in the worst-case scenario, he and other farmers — organic or not — might have to invest in new crops.
“I’d be lying if I said I wasn’t already looking at alternatives to citrus. Wine grapes are a possibility out here. And houses. That would be a good crop.”
In spite of the quarantine levied against San Diego and Imperial counties last summer, 17 Asian citrus psyllids were discovered in early March near Niland, in northern Imperial County. The quarantine zone was subsequently edged northward to include part of Riverside County, but this abrupt jump reveals just how easily a moderate breeze could dash all efforts to control the psyllid. Exactly how the insect first arrived in Tijuana and San Diego no one knows, but the likelihood is very real that the disease is already here. That would give the industry several years before the first branches turn yellow and the first fruits go blotchy green.