New discoveries of Asian citrus psyllids are cause for heightened concern in California groves, but the San Joaquin Valley's climate may help insulate it from the pest and the destructive disease it carries. 

The California citrus industry will not soon forget the week of Aug. 24.

First came the revelation that a handful of Asian citrus psyllids had been found in Santa Ana, nearly 100 miles north of the only other finds of the pest in the U.S. The following day, the California Department of Food and Agriculture confirmed another find farther north in metropolitan Los Angeles.


Both announcements came a week after confirmation from the Mexican government that the bacterial disease huanglongbing had been confirmed on the Yucatan peninsula.


Just mentioning the psyllid sends shudders down the spine of the California citrus industry because the pest is the only known carrier of the disease.

Huanglongbing is terminal for all citrus varieties, and there is no known cure.


That the psyllids seem to be moving rapidly north came as no surprise to at least one leading California researcher.


“We’ve been expecting this because the animal went through Florida very fast,” said Beth Grafton-Cardwell, a Tulare County-based integrated pest management specialist and a faculty member of the University of California-Riverside.


At week’s end, CDFA revealed an inspection dog in Sacramento identified a package containing guava and curry leaves shipped from Texas contained about 100 psyllids.


It is that type of movement that most concerns the industry and Grafton-Cardwell.


“The big battle is the volume of people and plant material that gets moved around the state on a daily basis,” she said.


Making matters more difficult is that there are thousands of host trees and plants in the southern half of the state.


“Sixty percent of homeowners in Southern California have citrus trees in their yards,” Grafton-Cardwell said.


The prognosis for the California citrus industry is not good.


“The disease will march its way across Mexico and ultimately into California, and then the psyllid will start running with it,” Grafton-Cardwell said. “I would guess it will take five to 10 years.”


At the same time, she believes there’s a strong probability HLB already is in California in a citrus tree or in a plant brought from Asia.


“Someone brought in some plant material, grafted it, created a tree in the backyard, and the disease is just sitting there waiting for the psyllid to find it,” Grafton-Cardwell said.


A limited silver lining


HLB has forced Florida growers to destroy or abandon 200,000 acres of citrus. Even if the disease gets a foothold in California, it may not be a death sentence for the state’s citrus industry, Grafton-Cardwell said.


“I don’t think it necessarily means the entire citrus industry will shut down,” she said. “Some areas of California will be worse off than others.”


The psyllid will struggle to survive in the summer heat and the winter cold of the San Joaquin Valley, Grafton-Cardwell said.


“But it will do very nicely in Southern California and along the coast,” she said. “It certainly will be more expensive to produce the fruit and more of a struggle. We just have to hope researchers can come up with tools to manage the psyllid and the disease.”


A small consolation


The Asian citrus psyllid was first discovered on the Pacific Coast in June 2008 in and around Tijuana, Mexico.


Within weeks, another infestation was identified in the San Diego suburb of Chula Vista, about 10 miles from the U.S.-Mexico border. Still other finds followed about 100 miles east of San Diego in Imperial County, another border county.


The finds in Santa Ana and Los Angeles were tempered by confirmation that none of the psyllids found in Santa Ana was carrying HLB, just as none of the pests found in San Diego and Imperial counties was a carrier.


The citrus industry will not be alone in feeling the effects of HLB should infestations take hold. Urban dwellers are going to lose the citrus trees in their yards, Grafton-Cardwell said, and “the industry is going to have import trees from heaven knows where to be able to recover.” 


Another guardedly positive note is that there have been no psyllid finds through Aug. 20 in the commercial citrus growing region of northern San Diego County, said Bob Blakely, director of grower services for California Citrus Mutual, Exeter. The psyllids somehow jumped from the border to urban areas of Orange and Los Angeles counties.


“It could have come up on plant material, hidden in someone’s car or even been carried on the winds that circulate around the Channel Islands and back to land,” Blakely said.


On Aug. 28, CDFA placed Orange County under a quarantine regulating the movement of citrus and other potential host plants. Treatments in the Santa Ana neighborhood where the psyllids were trapped were under way. Similar treatments continue in San Diego and Imperial counties.


“The treatments have been fairly effective in reducing the numbers to such low levels that they can’t find it again after the treatments.”  Grafton-Cardwell said. “If we can keep it in Southern California as long as possible, that’s the best we can do.”


California’s annual citrus production averaged 3.2 million tons 2006-08, according to the Economic Research Service of the U.S. Department of Agriculture.


The state produces 80% of the nation’s fresh-market oranges and 87% of the nation’s lemons, according to the service.

For more information on citrus greening, visit The Packer’s sister publication The Grower,  which has an online citrus greening resource center.