Asian citrus psyllids feed on citrus leaves and stems. The species was discovered around Daly City, Pacifica and South San Francisco. (Courtesey Citrus Pest & Disease Prevention Program)

Destructive citrus tree pest found in Peninsula

San Mateo County officials are urging residents to refrain from transporting citrus trees out of Daly City, Pacifica or South San Francisco after confirming the presence of an invasive insect species that can carry a citrus crop-destroying disease.
The Asian citrus psyllid is a type of jumping plant louse that carries Huanglongbing — a bacterial tree infection for which there is no cure. Infected trees can produce misshapen and bitter fruit. While the affected fruit is harmless to humans and it’s possible for an infected tree to be asymptomatic, all infected trees eventually die.

Officials also advise against transporting cuttings or green waste from citrus trees.

San Mateo County Agricultural Commissioner Fred Crowder said the county uses collection traps throughout the Peninsula to monitor for the presence of potentially harmful insects. Asian citrus psyllids were found in Daly City Oct. 28, and in Pacifica Nov. 6.

The quarantine zone includes everything within a five-mile radius of each collection site, Crowder explained, so South San Francisco is also included.

Crowder noted although San Mateo County has no citrus industry, trees growing in neighborhoods are vulnerable to the psyllids. Orange, mock orange, lemon, lime, grapefruit, sapote and pomelo are among the varieties attacked by the insects and the bacteria they carry.

Beyond San Mateo County, the stakes are high for California’s citrus farmers. The Asian citrus psyllid and Huanglongbing have gained footholds in all of Florida’s citrus-producing counties, costing that state an estimated 6,600 jobs and $3.6 billion in economic activity.

California growers are concerned, Crowder said, because the Asian citrus psyllid has become established in Southern California, and Huanglongbing has been detected there. And both could spread to the Central Valley, Crowder noted.

California Department of Food and Agriculture spokesman Jay Van Rein noted citrus is a $2 billion annual crop in California, with the industry directly employing about 10,000 workers, and indirectly supporting another 12,000 jobs in related fields and packing houses.

“All of that is at risk with a disease like this, because there is no known cure or treatment,” Van Rein said, “Trees that get the disease will decline and die within a few years.”

Fortunately, Huanglongbing cannot spread by itself. Without the presence of the insects that carry the disease, tree-to-tree infection is not possible. But bad decisions by humans can help both to spread, Crowder said.

When Huanglongbing was detected in the Southern California city of Hacienda Heights in 2012, authorities believe the culprit may have been a resident who brought tree cuttings home from a trip to Asia and grafted them onto a privately owned tree.
“If you graft infected cuttings onto a local tree, it becomes infected,” Crowder said.

Huanglongbing has not limited itself to the Hacienda Heights quarantine zone, Crowder said, noting earlier this year, it was found in San Gabriel.

Unlike the Mediterranean fruit fly, which devastated California crops in the 1980s, the Asian citrus psyllid’s eggs and larvae are not found inside fruit. Citrus fruits themselves can therefore be transported without risk of spreading the insects.
Branches, leaves and cuttings can easily harbor the bugs and their eggs, however, and Crowder noted the creatures are so small during some parts of their life cycles, they might be hard to detect visually.

Pacifica, Daly City and South San Francisco residents should therefore refrain from having branches or leaves from citrus trees hauled away, Crowder said. Instead, the county recommends keeping the green waste and composting it on-site.

For more information, visit http://californiacitrusthreat.org.

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