Environmental suitability of the San Joaquin Valley in relation to trap servicing interval
Dr. Robin Choudhury
In the fall of 2020, the ACP-detection trapping program in the San Joaquin Valley was operated on a bi-weekly schedule, although the CDFA Action Plan dictates a monthly schedule. DATOC was requested to provide input on whether the program should shift to a monthly schedule or amend the Action Plan to indicate that bi-weekly trapping should be continued.
This report proposes that the delimitation radius for tree surveys around an HLB+ tree be reduced from 400m to 300m. This change is suggested based on the geographic distribution of all trees confirmed to be positive for huanglongbing by March 2020, based on a methodology previously used by the CPDPC to make operational decisions.
Residential buffer zones around commercial citrus can be treated by CDFA with insecticides to suppress Asian citrus psyllid populations only if 90% of growers in that region apply insecticides within a designated 3-week window. While useful, this threshold created logistical difficulties and a new criterion for treatment was explored.
The DATOC expert panel feels strongly that the find of a single Asian citrus psyllid (ACP) in an area which is not generally infested and eradication is still being attempted should trigger a treatment area around the detection that is never less than a 400 m radius.
The CDFA action plan previously called for sampling 25% of an orchard should HLB be found within 400m. Best available evidence indicated that would be inefficient. DATOC suggested an evidence-based replacement plan, which was approved in March 2019.
DATOC compiled available research to help the CPDPC advise growers on how they should respond to an HLB find in or near their commercial grove. This was the basis of the "Best Management Practices in Response to Huanglongbing in California Citrus", approved by the CPDPC and published on CitrusInsider.org.
As a part of DATOC's report on exposure to CLas in Southern California residential areas, DATOC was asked to evaluate exposure over smaller geographic scales. We also evaluated the changes in infection density in the most recent detections.
Dr. Dave Bartels of the USDA has previously provided cluster maps to various groups. DATOC will be assuming responsibility for the production of these maps to provide the CPDPP committees with on-going analysis of the epidemic, to help with resource allocation decisions
The presence of ACP in California has been tracked by various programs and projects for several years. This analysis will construct a time series for various California regions since the start of these activities.
The CDFA recently implemented a pilot program which will allow citrus growers to utilize grates as an alternative mitigation strategy for disinfesting loads of bulk citrus. DATOC is analyzing the results of this program to help inform a recommended sampling plan if the grate systems are adopted on a wider scale.