Evaluating Exposure to HLB

As the number of known positive trees increases, the number of trees that must be sampled increases geometrically. An alternative tactic would be to make use of the wording in the agriculture code that allows for the mandatory removal of plants "exposed" to a quarantine pathogen or pest.  Such trees could be removed without the need for testing. The issue, then, is to define a radius around a known positive that constitutes the "exposed" area.
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An executive summary detailing this project's findings was released November 7, 2018.
Project Timeline

February, 2018

Project began.

March 7, 2018

Neil McRoberts reported to the CPDPC Operations Subcommittee. The project team is working on determining how quickly trees become infected in the HLB core area.

March 14, 2018

The project team reported to the CPDPC full committee on work done so far. The scope of the available data, a pre-definition of exposure, and a definition of exposure based on psyllid path, time, and distance were all discussed.

May 2, 2018

Project progress was reported to the CPDPC Science and Technology Subcommittee. Areas were identified of diffuse or dense spread, the latter of which should be used in exposure definitions, and quantified the number of trees an ACP may have visited after travelling 10 meters. The committee provided additional information to review to refine the work.

July 10, 2018

A report was given to the CPDPC Science and Technology Subcommittee. The analysis includes 237,196 tree samples, including 546 HLB+ trees, and 50,664 ACP samples, 139 of which were CLas+. Around 70% of trees in Southern California should be defined as exposed in areas where infected psyllids have been detected. The overall proportion of infected psyllids in all counties in CA was higher than the overall proportion of infected psyllids in areas with HLB, indicating that primary infections may be operating at a higher rate outside of the existing infection zone, and secondary infections are driving most of the discovered infections. 

October, 2018

Work on the project continues, with researchers determining how fast an infected tree appears based on the first date of psyllid presence, CLas+ positive psyllids, and HLB+ trees. Researchers are working on determining the likelihood of infection based on presence of the nearest CLas+ psyllid or HLB+ tree. They are finalizing the working data and models with the goal of providing actionable information and wrapping the project up by November.

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November 7, 2018

Preliminary findings were reported to the CPDPC Operations subcommittee, and an exectutive summary was produced. 

November 7, 2018

Preliminary findings were reported to the CPDPC Operations subcommittee, and an exectutive summary was produced. 

March, 2019

The full report was submitted to the CPDPP, including an additional section discussing exposure in commercial citrus orchards.

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DATOC is sponsored by the Citrus Research Board and the California Citrus Pest and Disease Prevention Program.