Engaging citizen scientists is becoming an increasingly popular technique for collecting large amounts of ecological data while also creating an avenue for outreach and public support for research. Here we describe a unique study, in which citizen scientists played a key role in the spatial prediction of an emerging infectious disease. The yearly citizen‐science program called “Sudden Oak Death (SOD) Blitz” engages and educates volunteers in detecting the causal pathogen during peak windows of seasonal disease expression. We used these data – many of which were collected from under‐sampled urban ecosystems – to develop predictive maps of disease risk and to inform stakeholders on where they should prioritize management efforts. We found that continuing the SOD Blitz program over 6 consecutive years improved our understanding of disease dynamics and increased the accuracy of our predictive models. We also found that self‐identified non‐professionals were just as capable of detecting the disease as were professionals. Our results indicate that using long‐term citizen‐science data to predict the risk of emerging infectious plant diseases in urban ecosystems holds substantial promise.

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The ability of metalaxyl-M, phosphonic acid in the form of phosphonate, and copper hydroxide to inhibit different stages in the life cycle of Phytophthora ramorum , the causal agent of sudden oak death (SOD), was tested in vitro using 12 isolates from the North American forest lineage. In addition, experiments were conducted in planta to study the ability of phosphonic acid injections and metalaxyl-M drenches to control pathogen growth on saplings of California coast live oak ( Quercus agrifolia ), and of copper hydroxide foliar sprays to control infection of California bay laurel ( Umbellularia californica ) leaves. Phytophthora ramorum was only moderately sensitive to phosphonic acid in vitro , but was highly sensitive to copper hydroxide. In planta experiments indicated the broad efficacy of phosphonic acid injections and of copper hydroxide sprays in preventing growth of P. ramorum in oaks and bay laurels, respectively. Finally, although metalaxyl-M was effective in vitro , drenches of potted oak trees using this active ingredient were largely ineffective in reducing the growth rate of the pathogen in planta .