Blight Threatens California’s Citrus Trees

University of FloridaAn Asian citrus psyllid feeding on liquid inside a citrus tree.

In a worrisome development for citrus growers in California, or anybody there who has a beloved lemon or orange tree in the yard, the citrus disease huanglongbing, or citrus greening, has been found in southeastern Los Angeles County, the California Department of Food and Agriculture reports.

It’s the first time the disease, one of the most serious scourges of citrus, has been reported in the state.

“It’s a gut shot,” Joel Nelsen, president of industry group California Citrus Mutual, said in a telephone interview. “We’ve been looking for this, and unfortunately we’ve found it.”

University of FloridaCitrus greening causes yellow mottling on the leaves of citrus trees.

The disease is caused by a bacterium that is thought to have originated in China and is spread by the Asian citrus psyllid, a pest that feeds on citrus trees and other plants. Thebacteria attack the trees’ phloem, or vascular tissue, preventing the transport of nutrients. Once infected, trees die within about five years; despite years of research, there is no known cure or treatment for the disease.

Found in Florida in 2005, the disease has already killed millions of trees and devastated growers throughout the state. The University of Florida estimates that citrus greening has caused the loss of 6,600 industry jobs and erased $3.6 billion in revenue.

Mr. Nelsen said he and others connected to California’s $2 billion citrus industry were “very worried.”

State officials removed the infected tree, a lemon-grapefruit hybrid, from a yard in the Hacienda Heights section of Los Angeles County and haveannounced measures to help prevent the spread of the disease like setting up a local quarantine zone, creating traps for infected insects and selectively spraying insecticide. No citrus plants or nursery stock may be removed from the area.

The greatest immediate threat may be to the homeowners of Los Angeles County, 60 percent of who have a citrus tree in their yard, said Elizabeth Grafton-Cardwell, an extension specialist and researcher at the University of California, Riverside.

Homeowners in the county and throughout Southern California are urged to report potential symptoms like yellow mottling of leaves and misshapen, bad-tasting fruit. There’s even an iPhone app for reporting potential instances of disease called Save Our Citrus.

The Asian citrus psyllid made its way into California from Mexico four years ago. Quarantines are in place where the flying plant lice have been reported within eight counties in the southern part of the state. The pest is not a huge menace by itself although it can quickly spread the bacteria responsible for citrus greening.

The majority of the state’s citrus crop is found is in the San Joaquin Valley about 120 miles north of Hacienda Heights, Mr. Nelsen said. The nearest commercial groves are about 40 miles away, in Riverside; psyllids can travel about six miles a day on their own, he said.

The citrus greening bacteria probably spread from the cutting of bud-wood illegally brought in from outside the country, Dr. Grafton-Cardwell said. Similarly, Mr. Nelsen suggested that the likely culprit was a local hobbyist who started new citrus trees from imported cuttings.