Insect that can be deadly for citrus plants detected in San Mateo County

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An invasive insect recently detected in areas of Redwood City and Foster City have prompted officials to set traps and establish a quarantine regulating the movement of all citrus trees and citrus plant materials in affected areas.

Two Asian citrus psyllids known to carry and spread a deadly plant disease known as Huanglongbing to citrus trees and plant materials were confirmed in Foster City on Wednesday, Jan. 23, and in Redwood City on Friday, Feb. 1.

“Huanglongbing disease is not harmful to humans or animals, and though unappetizing, citrus fruit infected with the disease is safe to eat,” county officials said.

In response, the San Mateo County Agricultural Commissioner and California Department of Food and Agriculture (CDFA) are beginning a survey and treatment program. Traps throughout the area will be set to determine the presence and extent of a larger breeding population, and citrus host plants within 50 meters of the site where the insect was trapped will be treated. 

“Residents within the treatment area will be notified in advance and community outreach meetings are being planned,” the county said.

To prevent further movement of the insect, the CDFA is establishing a quarantine. Homeowners are asked not to move citrus trees, citrus plant parts, or foliage of citrus trees outside of the Asian Citrus Psyllid Regional Quarantine. A map of this quarantine can be found here and here.

Huanglongbing is also being eradicated in areas of Los Angeles, Orange and Riverside counties. Researchers are searching for a cure for the disease, which killed enough citrus plants in Florida from 2005 to 2012 that it caused the loss of over 6,600 jobs and $3.6 billion in economic activity in the state. With California being the second-largest citrus producer in the nation, the county says it’s important to manage the pests.

“The Asian citrus psyllid combined with Huanglongbing disease is a lethal combination for all citrus,” said San Mateo County Agricultural Commissioner Fred Crowder. “With the community’s support, our goal is to eradicate Asian citrus psyllid.  This both protects our state’s vital citrus industry, as well as our mature backyard lemon, orange, mandarin, lime and other mature, fruit-producing citrus trees grown at family homes throughout the region.  Working together as a community we can protect and save our citrus trees.”   

Residents who think they may have seen the pest are urged to call the Pest Hotline at 800-491-1899.  For more information, visit: or