Gummy stem blight (GSB), caused by three Stagonosporopsis species, is one of the most important diseases of watermelon in the southeastern U.S. Since there is currently no commercial resistance for GSB in watermelon cultivars, its management depends on cultural practices and costly preventive fungicide applications. The three Stagonosporopsis species exhibit differential sensitivity to some of the most commonly used fungicide chemistries and they cause the same type of symptoms in the field, which results in a need for the identification of the specific species causing disease at a given time to enable more responsive decision-making in terms of management. In order to accomplish this, efficient methods for pathogen detection and point-of-care (POC) diagnosis are required. The first study sought to design, develop and optimize loop-mediated isothermal amplification (LAMP) assays for the specific detection of the Stagonosporopsis species that cause GSB under two detection formats that can be easily field deployed. In this study, an S. citrulli-specific LAMP assay was developed, which is very sensitive for the detection of relatively small amounts of pathogen gDNA (1 pg.). A second study sought to develop a detection system for the GSB pathogens that can be used on-site in watermelon fields and transplant greenhouses. We developed and tested a spore sampling system intended to trap airborne ascospores and potentially water-splashed conidia. Collected samples were subjected to diagnosis using a reliable molecular assay for pathogen detection and confirmation and in the process, two quick DNA extraction protocols for both pathogen spores caught by the trapping system, and samples collected from leaves were developed and optimized. Fungicide applications were also saved based on the sampling and detection of GSB pathogens during the crop season. Finally, a third study involved testing a chlorophyll fluorescence (CF) and multispectral imaging system for early detection of GSB disease symptoms in watermelon seedlings. Our goal was to detect stress-related irregularities related to GSB and to provide the basis for evaluating potential correlations between CF and multispectral vegetation indexes, and the pathogen’s presence and disease progress and development.