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We report on the use of a non-instrumented device for the implementation of a loop-mediated amplification (LAMP) based assay for the select-agent bacterial-wilt pathogen Ralstonia solanacearum race 3 biovar 2. Heat energy is generated within the device by the exothermic hydration of calcium oxide, and the reaction temperature is regulated by storing latent energy at the melting temperature of a renewable lipid-based engineered phase-change material. Endpoint detection of the LAMP reaction is achieved without opening the reaction tube by observing the fluorescence of an innovative FRET-based hybridization probe with a simple custom fluorometer. Non-instrumented devices could maintain reactions near the design temperature of 63C for at least an hour. Using this approach DNA extracted from the pathogen could be detected at fewer than ten copies within a 25 L reaction mix, illustrating the potential of these technologies for simple, powerful agricultural diagnostics in the field. Furthermore, the assay was just as reliable when implemented in a tropical environment at 31C as it was when implemented in an air-conditioned lab maintained at 22C, illustrating the potential value of the technology for field conditions in the tropics and subtropics.