Risk-based HLB surveys: for southern California, statewide and targeted - an analysis of the increasing risk of HLB over the last five years

Authors: Gottwald, Timothy; LUO, WEIQI - North Carolina State University; MCROBERTS, NEIL - University Of California, Davis

Submitted to: Citrograph
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2017
Publication Date: 12/10/2017
Citation: Gottwald, Timothy, Luo, Weiqi, McRoberts, Neil. 2017. Risk-based HLB surveys: for southern California, statewide and targeted - an analysis of the increasing risk of HLB over the last five years. Citrograph. 9(1):38-43.

Interpretive Summary: Evidence from Florida, and other citrus-producing areas of the world, clearly demonstrates that huanglongbing (HLB) is not a disease that can be managed effectively by individual growers. Rather, it is a disease which confronts the whole production industry and other stakeholders simultaneously. Further HLB outbreaks in Southern California are inevitable over time as ACP populations and CLas inoculum continue to increase. The overarching goal is the earliest possible detection of HLB outside the epidemic zone, before the pathogen Candidatus Liberibacter asiaticus (CLas) becomes established providing time and opportunity for eradication and preservation of the California citrus industry. Integration of statewide and targeted risk-based HLB survey provide an early detection and decision making tool for regulatory agencies and citrus producers to optimize eradication/mitigation efforts. The survey results also provide a systematic means to monitor disease progress for various areas of concern in Southern California. Depending on the management purpose, regulatory agencies can use the survey results to balance how much sampling effort should be dedicated towards statewide survey (e.g. capturing global disease situation) versus targeted survey (e.g. focusing local disease outbreak). Although designed specifically for HLB/ACP survey this framework can be transferred easily to other potential exotic pest/disease invasion applications (e.g. citrus pests for other citrus producing areas in CA and other states).

Technical Abstract: Evidence from Florida, and other citrus-producing areas of the world, clearly demonstrates that huanglongbing (HLB) is not a disease that can be managed effectively by individual growers. Rather, it is a disease which confronts the whole production industry and other stakeholders simultaneously. The importance of an effective early detection system for HLB in California is increased by the existence of the large and diverse commercial citrus industry and extensive residential citrus population. Since 2013, we have developed and continuously refined a risk-based survey design that addresses the urgent need to respond to the HLB threat. The survey anticipates pathogen introduction and spread on state-wide, strategic and systematic levels, rather than waiting for disease to appear locally. Up to now, the risk-based survey model has resulted in multiple HLB discoveries in Southern California, and served as a predictive tool for decision making and disease management. The risk-based survey is implemented at two major spatial scales: statewide and targeted. Statewide survey captures the immediate HLB situation and informs high risk areas via early detection. Targeted survey examines new HLB detections outside existing quarantine regions resulting from the statewide survey. Targeted sampling augments efforts to increase the probability of follow-up HLB detection for mitigation/management aimed at maintaining low incidence and suppressing a severe impending epidemic.