San Diego County

Citrus Tree-Killing Bacteria Found on Insects for First Time in SD County

The bacteria, which is not harmful to people or animals, was detected on insects in the North County community

adult Asian citrus psyllids
County News Center

State agricultural inspectors have detected bacteria which can cause a disease deadly to citrus trees during routine pest trapping in Fallbrook, San Diego County officials announced Thursday.

The bacteria, which is not harmful to people or animals, was detected on insects in the North County community.

A routine spot check by the California Department of Food & Agriculture on Dec. 28 collected a group of four adult Asian citrus psyllids from a citrus tree on residential property in the Fallbrook area carrying the bacteria Candidatus Liberibacter asiaticus.

These bacteria can cause a citrus disease called Huanglongbing. At this time, the disease has not been detected in citrus trees in San Diego County. Samples from trees on that property and the surrounding area were undergoing tests for the disease, which is fatal to citrus trees and has no cure.

Results should be available the week of Jan. 4. If the test results are positive on the foliage, then a five-mile quarantine for the disease will be triggered.

The disease is considered a major threat to San Diego County's $150 million annual citrus crop and can impact residential citrus tree growers with misshapen, bitter fruit and eventually kill the tree.

"Rapidly detecting and controlling the spread of the Asian citrus psyllids that carries Huanglongbing continues to be a priority for the County," said San Diego Agricultural Commissioner Ha Dang. "While ACPs are frequently found in our ongoing mitigation efforts, the bacteria have never been found locally before."

"We are working closely with our residents, growers, and industry partners to limit any potential impact and will keep everyone informed moving forward," she added.

The detection of the bacteria triggers additional sampling and testing of both citrus trees and the insects on residential properties in a 250-meter area surrounding the detection site. The county department of Agriculture, Weights and Measures and the state food and agriculture department will work with residents in the immediate area to arrange for treatment of citrus trees -- on a voluntary basis -- as a protective measure against the insects and Huanglongbing infestation.

County officials are also proactively notifying local citrus growers, plant nurseries and other related businesses. If the disease is detected in citrus trees in the area, agricultural officials will follow up with removal of the infected trees, additional treatment of nearby citrus trees, heightened trapping efforts and a quarantine to restrict the movement of citrus trees, fruit and foliage.

While this is the first time that the tree-killing bacteria has been discovered in San Diego County, the Asian citrus psyllids have been detected here before, in 2008. Surveys, insect trapping, tree sampling and other regulatory activities have been ongoing throughout the county since then. The bacteria has previously been confirmed in portions of Los Angeles, Orange, San Bernardino and Riverside counties.

The psyllids have been frequently found in San Diego, Imperial, Riverside, San Bernardino, Orange, Los Angeles, Santa Barbara and Ventura counties.

Huanglongbing is a bacterial disease that affects the vascular system of citrus plants. HLB-infected trees bear small, asymmetrical fruit that is partially green, bitter, and not fit for sale or consumption. The disease destroys the appearance and economic value of the trees and eventually causes their death, typically within a few years. Infected trees may have areas with mottled yellow leaves, generally seen in asymmetrical patterns.

Residents can take a number of steps to help ward off or contain disease including:

  • Not taking or moving cuttings from backyard citrus plants from one
    property to another;
  • Buying citrus trees only from reputable local nurseries;
  • Cooperating if county or state inspectors ask to place insect traps on their land; and
  • Reporting citrus trees and plants that seem to be sick or dying -- even though they also appear to be well-watered and well-maintained -- by contacting the San Diego Department of Agriculture, Weights, and Measures at 760-752-4700 or going to Residents can also call CDFA's toll-free Pest Hotline at 800-491-1899 or go to

Contact Us