IntroductionPhytophthora ramorumis a quarantine pathogen that causes leaf blight and shoot dieback of the crown, bark cankers and death on a number of both ornamental and forest trees, especially in North America and northern Europe, where it has produced severe outbreaks. Symptoms caused byP. ramorumcan be confused with those by otherPhytophthoraand fungal species. Early and accurate detection of the causal pathogenP. ramorumis crucial for effective prevention and control of Sudden Oak Death.MethodsIn this study, we developed aP. ramorumdetection technique based on a combination of recombinase polymerase amplification (RPA) with CRISPR/Cas12a technology (termed RPACRISPR/ Cas12a).ResultsThis novel method can be utilized for the molecular identification ofP. ramorumunder UV light and readout coming from fluorophores, and can specifically detectP. ramorumat DNA concentrations as low as 100 pg within 25 min at 37°C.DiscussionWe have developed a simple, rapid, sensitive, unaided-eye visualization, RPA CRISPR/Cas12a-based detection system for the molecular identification ofP. ramorumthat does not require technical expertise or expensive ancillary equipment. And this system is sensitive for both standard laboratory samples and samples from the field.