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How where and when to control an established plant disease epidemic. Landscape-scale modeling of sudden oak death in California

Nik Cunniffe: University of Cambridge

<div>We use mathematical modelling to analyse control of sudden oak death in California. Sudden oak death, caused by the oomycete <em>Phytophthora ramorum</em>, has killed millions of oak and tanoak in California since its first detection in 1995. Despite some localised small-scale management, there has been no large-scale control in California to date. However, much information from both basic and applied research has accumulated over the past two decades, and we now have a good understanding of <em>P. ramorum</em> epidemiology. Mathematical models have been developed which integrate this knowledge, providing us with the opportunity to use modelling to test “what if” scenarios concerning management. </p> <p>We therefore use the Californian epidemic as a case study to illustrate how modelling can address general issues for invading epidemics. How quickly must control start for it to be effective? When is an epidemic so large that effective control is impossible? How should local treatment be deployed around infected sites? How does this depend on the available budget and level of risk aversion? Which sites should be targeted for control when there is insufficient resource to treat all infected locations? How can expenditure on detection and control be balanced? What is the effect of a budget that changes over time? The epidemiological principles underlying these questions are important for control of all invasive plant pathogens.</div>