Virtual meeting addresses Asian citrus psyllid finds in Fallbrook

A Jan. 12 virtual meeting addressed the finds of Asian citrus psyllids in Fallbrook.

The meeting was hosted by the state's Citrus Pest and Disease Prevention Program, which is funded by California growers and administered by the California Department of Food and Agriculture. Citrus Pest and Disease Prevention Program liaison Sandra Zwaal provided an overview and gave the presentation on an Asian citrus psyllid testing positive for candidatus liberibacter asiaticus, a bacteria which causes huanglongbing disease.

Karina Chu and Keith Okasaki from CDFA discussed HLB regulations. Jason Schwartze and Travis Elder from the County of San Diego's Department of Agriculture, Weights and Measures addressed updates from the office of the County Agricultural Commissioner. Monique Rivera from the University of California, Riverside provided updates on Asian citrus psyllid and HLB research.

The Asian citrus psyllid is a vector of the bacteria candidatus liberibacter africanus, candidatus liberibacter asiaticus, and candidatus liberibacter americanus. The bacteria can cause HLB, and an Asian citrus psyllid can transmit HLB from an infected tree to a healthy one.

The first ACP find in San Diego County was in 2008, and the first find in North County was in Valley Center in 2009. The first known case of HLB in California was in Los Angeles County in 2012. Currently there have been no cases of HLB in San Diego County.

"Citrus trees are routinely surveyed," Zwaal said.

An ACP find results in analysis. "Those samples are then taken to the lab and tested for CLAs," Zwaal said. "When CLAs are confirmed in adult ACPs, it sets up other actions."

On Dec. 28, a routine inspection in a Fallbrook residential neighborhood by Fallbrook High School found four Asian citrus psyllids. Subsequent testing revealed that the psyllids had candidatus liberibacter asiaticus.

All citrus trees within 250 meters of the find were surveyed. "It's good news that we have no commercial sites within that 250 meter area," Zwaal said.

A commercial site is defined as one with at least 25 trees regardless of whether the produce is actually sold at market.

The follow-up determined that there was no bacteria in the plant tissue itself. "Next time we may not be so lucky," Zwaal said.

"Sampling will continue throughout the adjacent sites," Zwaal said. "It is important that citrus growers stay diligent."

Orchards will be monitored for psyllids. "It's important to apply your ACP treatment," Zwaal said.

HLB is not spread evenly throughout the tree, so part of an infected tree might test positive while another part of the tree would test negative.

"Once HLB hits an area, it starts progressing fairly quickly," Zwaal said. "It is a positive tree that would trigger an HLB quarantine."

A quarantine would apply for a five-mile radius around any infected tree. Citrus can be transported out of a quarantine area if mitigation methods have been undertaken. The mitigation options include spraying and harvesting, post-harvest treatment, and field cleaning by machine. "Grate cleaning is an alternative mitigation method," Chu said.

Grate cleaning involves cutting short the stems and dumping the fruit on the grates. Gravity will roll the fruit so that the leaves and stems drop through the grate, and rolling the fruit also causes the psyllids to dislodge from the citrus.

The process for approval of a grate cleaning system begins with submission of a written proposal to the county agriculture commissioner, who will review the proposal along with CDFA staff. Grate special instructions may be added to the compliance agreement. Approval also includes county agriculture department and CDFA inspections.

An ACP-free declaration form must be submitted to the county agriculture commissioner no less than 72 hours prior to harvest, and a copy of the declaration form must be provided to the receiving packer or processor upon delivery. If the citrus is shipped to another county that county's agricultural commissioner must receive a copy of the declaration form at least 24 hours in advance of the shipment.

"There should be no stems and leaves in the fruit at the market," Okasaki said.

"It's an arduous process, but it's streamlined," Schwartze said.

Transport from a quarantine area requires the fruit to be completely tarped or in a fully enclosed vehicle.

Nursery growers can enter into a pre-quarantine agreement. "It is an optional agreement," Elder said.

Such an agreement would only cover trees or other stock which is fully enclosed. "Everything that's outdoors you'll have to think of something to do with it," Elder said.

The cost of the agreement is estimated at between $1,000 and $2,000. "Some people see it as an insurance policy," Elder said.

The lifecycle of an Asian citrus psyllid through the egg, larvae, pupae, and adult process is approximately two months. An Asian citrus psyllid can travel approximately 2,500 feet over a 12-day period. "They mostly do short flights," Rivera said.

"The less psyllids you have the less chance you have for your grove to succumb to the pathogen when it develops," Rivera said. "That's the only way at this point that we can truly prevent this spreading."

A recently-funded project seeks to determine the relationship between the psyllids and HLB. "The goal of this project is to determine the percent of HLB positive psyllids," Rivera said.

"It's critical to understand how many of these HLB positive psyllids are out there," Rivera said. "This is going to help us answer some of the questions about risk."

The research will also attempt to determine the percentage of color morphs in the field. Asian citrus psyllids have blue-green, grey, and orange morphs. "The orange are more susceptible to infected diets," Rivera said.

The study plans to analyze 13,680 insects from 15 sites in San Diego, Riverside, San Bernardino, and Ventura Counties over a two-year period. "If you're going to sample insects you need to do it consistently over time," Rivera said.