The Asian citrus psyllid is an invasive species carrying a bacterial infection, known to kill any citrus tree that becomes infected. (Courtesy Photo)

Second confirmation of citrus-destroying pest reported in San Mateo County

San Mateo County officials are expanding mitigation efforts after again detecting an insect that carries a disease lethal to citrus trees.

The Asian citrus psyllid is an aphid-like invasive species that can carry a bacterial infection called Huanglongbing, which is harmless to humans, but kills any citrus tree that becomes infected.

The second confirmation of an Asian citrus psyllid in Pacifica happened about a mile from the original detection site in Daly City. If the insects are found at just one site in a given area, the county treats every citrus tree within a 100-meter radius with insecticides, according to San Mateo County Agriculture Commissioner Fred Crowder.

But, Crowder explained, the detection of psyllids at two locations so close together has triggered the next level of mitigation, which calls
for every citrus tree within 400 meters of the detection sites to be treated.

San Mateo County officials instituted a quarantine and treatment program when the insect was detected in Daly City in late October and in Pacifica earlier this month.

The quarantine, as previously reported by the San Francisco Examiner, affects Pacifica, Daly City and South San Francisco. Crowder also said parts of Colma, Brisbane and San Bruno are quarantined.

Some southern parts of San Francisco bordering Daly City are also affected by the quarantine, but San Francisco Agriculture Commissioner Miguel Monroy could not be reached for comment.

The Asian citrus psyllid has also been found in Southern California, and could threaten the Central Valley’s citrus industry.

San Mateo County officials have asked residents to observe the quarantine by not transporting citrus trees or citrus tree cuttings in or out of the affected cities. Crowder urged residents to closely inspect their citrus trees and alert county officials if they find signs of infestation.

The agriculture commissioner added the insects are very small, and can be hard to detect with the naked eye.

Fruit from treated trees is safe to eat once the chemicals have dried, Crowder said, but he recommended washing the fruit prior to consumption.

To preserve bee populations, no spraying is done when the pollinators are present, Crowder noted, and monitoring equipment ensures air and soil quality aren’t unduly affected by the treatments.

It’s possible the psyllids have been in the area longer than authorities had believed, Crowder said, because multiple detection sites so close together could be evidence of a more longstanding presence.

“This indicates they may not be a recent arrival,” Crowder noted.

The county has been inspecting local nurseries and obtaining compliance agreements from vendors who sell citrus trees.

Home Depot has stores with garden centers in Daly City and Colma. Spokesman Matthew Harrigan said the chain only works with growers and suppliers who are proactive about combatting the Asian citrus psyllid.

“We work closely with our citrus growers to ensure the products we receive are compliant,” Harrigan said, “All our trees are tagged to show origin and handling.”

Fortunately, the Huanglongbing bacteria need the psyllids to spread, so tree-to-tree infection is impossible without the bugs.

Crowder suspects the climate in Pacifica and Daly City has prevented the psyllids from thriving, but he stressed that’s speculation on his part.

“The coast may be too cold for the psyllids to build a large population,” Crowder said, “The concern is if they migrate to the warmer bayside or some other warmer microclimate.”

The insect and bacteria have also been a major problem for citrus growers in Florida, costing the state thousands of jobs and billions of dollars in economic activity.

For information on protecting your citrus trees, visit http://californiacitrusthreat.org.

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