Abstract
Huanglongbing (HLB), or citrus greening, is a global citrus disease occurring in almost all citrus growing regions. It causes substantial economic burdens to individual growers, citrus industries and governments. Successful management strategies to reduce disease burden are desperately needed but with so many possible interventions and combinations thereof it is difficult to know which are worthwhile or cost-effective. We review how mathematical models have yielded useful insights into controlling disease spread for other vector-borne plant diseases, and the small number of mathematical models of HLB. We adapt a malaria model to HLB, by including temperature-dependent psyllid traits, “flushing” of trees, and economic costs, to show how models can be used to highlight the parameters that require more data collection or that should be targeted for intervention. We analyze the most common intervention strategy, insecticide spraying, to determine the most cost-effective spraying strategy. We find that fecundity and feeding rate of the vector require more experimental data collection, for wider temperatures ranges. Also, the best strategy for insecticide intervention is to spray for more days rather than pay extra for a more efficient spray. We conclude that mathematical models are able to provide useful recommendations for managing HLB spread.
Highlights
Huanglongbing (HLB), known as citrus greening disease, is a devastating citrus disease native to Asia (Bove, 2006; Gottwald, 2010; Hall et al, 2013) that exists in virtually all citrus-growing regions (Narouei-Khandan et al, 2016)
HLB is caused by three bacteria: Candidatus Liberibacter asiaticus (CLas), Candidatus Liberibacter africanus, and Candidatus Liberibacter americanus
We provide an example of how a mathematical model for malaria can be adapted to describe HLB transmission and the potential insights it can yield
Summary
Huanglongbing (HLB), known as citrus greening disease, is a devastating citrus disease native to Asia (Bove, 2006; Gottwald, 2010; Hall et al, 2013) that exists in virtually all citrus-growing regions (Narouei-Khandan et al, 2016). The work of Parry et al (2014) builds upon the framework of the mechanistic model by fitting a spatially explicit disease model in which trees are either Susceptible, Exposed, Infectious, Detected or Removed using data from Southern Garden’s citrus groves It is primarily a methods paper, using HLB as a case study. The authors include publiclyavailable software to allow stakeholders to interact with the model, to understand how a strategy of roguing within a radius of detected infected trees would be affected by different roguing radii and the stochastic nature of disease spread Their focus is on citrus canker but they include HLB as a second example, with the result that optimal roguing radii can be found dependent on the level of risk aversion of the grower. Cunniffe et al (2014), which focuses on Bahia bark scaling of citrus, illustrates that mathematical models are able to provide useful recommendations for roguing and tree spacing strategies, even when epidemiological knowledge of the disease is limited
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