Asian citrus psyllid study: Vigilance urged but ‘no cause for panic’

The Asian citrus psyllid is the insect vector for the bacterium that can cause huanglongbing disease. Photo credit: UC Regents

Preliminary results indicate 3.5% of ACP collected showed signs of bacterium that can cause huanglongbing

An ongoing study in the commercial citrus groves of coastal Southern California is looking at whether Asian citrus psyllids – the insect vector of huanglongbing “citrus greening” disease – are carrying the bacterium that can cause HLB.

Thus far, the project has tested more than 3,000 adult ACP collected from 15 commercial citrus sites across the region, of which 138 – just over 3.5% – had some level of the bacterium present, according to researchers from UC Agriculture and Natural Resources, UC Davis, UC Riverside and the University of Arizona, Tucson.

“While the results are a cause for concern, the situation in California is much better than in Florida and Texas, where ACP carrying the bacterium make up the majority of the population and HLB is widespread in commercial citrus,” said Neil McRoberts, a UC Davis plant pathologist and UC Integrated Pest Management program affiliate advisor. “The results indicate that there is no room for complacency, but also no cause for panic.”

Yellowing leaves can be one sign of huanglongbing, which has devastated the Florida citrus industry. Photo credit: UC Regents

Since the first HLB-infected tree in California was found in 2012, nearly 4,000 infected trees have been detected and removed from residential properties in Southern California, mainly in Orange and Los Angeles counties. According to McRoberts, “to date, no HLB has been found in commercial citrus” in California.

He stressed, however, that the aforementioned ACP study – funded by the HLB Multi Agency Coordination Group and managed by USDA-APHIS – does not involve any testing of trees for HLB and focuses only on looking at the insect which spreads the bacterium.

McRoberts also emphasized that the project's detections of the bacterium cannot be considered “official” because the researchers' lab procedures differ from the official testing protocols of the California Department of Food and Agriculture.

“Follow-up sampling by CDFA staff would allow official samples to be collected for further investigation, but is entirely voluntary for the growers involved,” he said, adding that his research team is currently wrapping up the sampling phase of the project, with data analysis continuing into 2023.

While commending the “huge coordinated effort” by the California citrus industry, California Department of Food and Agriculture, UC ANR and other partners to suppress the ACP vector and slow the spread of HLB, McRoberts also urged continued vigilance.

“Our study results indicate that it is not time to declare the emergency status for ACP/HLB in California over – the situation is still evolving,” he said.

For further information about the research, contact Neil McRoberts at nmcroberts@ucdavis.edu or (530) 752-3248.

Read more