California officials continue to find more Asian citrus psyllids (ACP) where their discoveries have either been limited or non-existent. While the finds generally continue to be one adult here and there in mostly urban settings, citrus industry officials believe more can be done to control the pest.

The California Department of Food and Agriculture reports yet another single adult psyllid was caught in a trap in an urban Bakersfield (Kern County) neighborhood. That is the second adult psyllid caught in a Bakersfield trap within a one-month period.

Probably of keener interest is the “breeding population” discovery of psyllids at two locations in the Bay Area city of San Jose.

The San Jose find is far-removed from the rest of the psyllid discoveries in California, which thus far has only been seen in counties several hundred miles south of the Bay Area. The closest discovery of psyllids to San Jose remains San Luis Obispo County on the Central Coast.

“The San Jose find may be an introduction through an airport or a hitchhiker that manifested itself into a large population,” said Joel Nelsen, president of the California Citrus Mutual, a commercial trade association. “We just don’t know.”

While citrus industry officials concede that southern California psyllid populations are well-established in counties from Los Angeles, southward, it’s the single finds in the southern San Joaquin Valley that raise more questions than answers.

“You can make the argument that the Ventura and San Luis Obispo discoveries show a northward progression of the psyllid, but I think there’s more to it than that,” said Nelsen.

Nelsen does not believe that the latest find in San Jose necessarily means that the ACP has migrated on its own from the Mexican border to the Bay Area in less than 10 years. The ACP was first discovered in California in 2008 and until the San Jose discovery, had been found only as far north as San Luis Obispo County and southern Fresno County.

Movement by man

Nelsen suspects the invasive pest is likely being introduced throughout the state by the movement of citrus plants, fruit and commercial harvesting equipment, though he does not discount the introduction through the illegal importation of citrus materials through international airports and parcel shipments.

That citrus plants and trees are more common in urban yards in California than they are in commercial settings, and that these plants go largely untreated for pest and disease by homeowners only increases the likelihood that the tiny pest can easily spread.

Citrus officials fear the pest because it is responsible for spreading a bacterial disease called Huanglongbing (HLB), or citrus greening. The disease only affects citrus and is not known to be a human health risk.

So far only one case of citrus greening has been confirmed in California. That happened in 2012 in a suburban Los Angeles neighborhood.

CDFA Public Affairs Director Steve Lyle says HLB testing continues on samples taken from trees throughout the state. With an increase of reported ACP finds in Tulare and Fresno counties, an HLB survey is currently under way in the two citrus-producing counties.

Nelsen believes the biggest culprit to the psyllid’s expansion has been mankind.

Because of the close proximity of citrus groves in the heavily-infested counties of Riverside and San Bernardino to regions like Ventura, San Luis Obispo and Kern counties, Nelsen believes that psyllids have successfully hitchhiked to other commercial growing regions on citrus equipment.

“I would argue that the industry still needs to be more diligent in cleaning harvesting equipment before moving it,” Nelsen said.

Nelsen and others in the citrus industry point to psyllid discoveries on traps at or near citrus packing sheds as examples of how the pest is being transported by commercial transport trucks throughout the state.

Kern County

The Bakersfield discoveries are significance because of the location of citrus south and east of the city.

While Kern County’s citrus region is separated from infestations in southern California by a small mountain range, it is connected by well-traveled transportation routes that make it easy for psyllids to migrate on citrus harvesting equipment, big rigs hauling citrus fruit, and quite possibly in the vehicles of growers traveling back and forth from their southern California citrus groves.

Ironically, Kern County has not had the large number of confirmed sightings of the psyllid that neighboring counties like Ventura or Tulare have seen.

Nelsen does not discount the movement of citrus plant materials by homeowners and others for the urban spread of the psyllid. According to Nelsen, it was the movement of a psyllid-infested tangerine tree from southern California to Dinuba that led to the discovery of a significant breeding population on a small tangerine tree in a residential neighborhood there.

“We either got lucky with that find or it proves our programs work,” Nelsen said of the Dinuba psyllid discovery. “It’s frightening to think what could have happened if we didn’t find that tree.”

Nelsen suggests that the reason California officials are finding the pests is due in part to the heightened awareness of them. While disconcerting, this is evidence that state programs to keep the ACP from commercial citrus groves is working.

Nelsen does not believe the ACP is spreading elsewhere in California as fast or effectively as it did across southern California, though he is nevertheless concerned about the pest.

Still, Nelsen remains confident that programs implemented in California have slowed the progression of the psyllid, and that other state efforts, including laws that control nursery stock, have prevented a rapid expansion of pest and disease throughout the state’s citrus growing region.

Officials admit that California has benefitted from watching the spread of the ACP and HLB in states like Florida and Texas. Through lessons learned in those states California has adapted its protocols to help slow the ACP in an effort to prevent HLB from infecting commercial citrus.

According to Nelsen the numerous international transportation access points in California where plant and fruit materials can be imported, allowing for invasive species to gain a foothold, only compounds California’s efforts to control the pest.

There appears to be effective buy-in by urban residents and the various regulatory agencies to help control the psyllid in California, Nelsen says.

California citrus producers currently contribute $750,000 per year towards public outreach programs to help urban residents understand the importance of controlling the ACP and why preventing HLB is important to urban and commercial citrus growers alike.

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