Technical Abstract: A multi-faceted, systems approach to downy mildew management continues to be developed in the U.S., and includes sporangia detection methods, epidemic modeling, and modified cultural practices to suppress the disease. During 9 location-years of validation of a PCR assay for detection of airborne Pseudoperonospora humuli, pathogen detection occurred no later than 8 days after the appearance of trace levels of disease or detection of airborne sporangia in a volumetric spore sampler. During evaluation in commercial yards, use of the PCR results to initiate the first fungicide application led to enhanced disease control or fungicide use reduction in four of six yards compared to growers’ standard practices. We also have developed and evaluated a degree-day model that forecasts the first emergence of shoots systemically infected with P. humuli and a risk index for secondary spread of the disease. During four growing seasons in western Oregon, the degree-day model provided on average 4.9 days (median -0.5 days) of advanced warning before the first spike emerged. Surveys of 34 commercial hop yards in Oregon indicated the downy mildew severity during the previous season was negatively correlated with the degree-day emergence date of spikes the following year (r = -0.391). In experimental plots, treatments initiated using a degree-day threshold had disease severity similar to or less than that of plots that received routine fungicide applications during three seasons of evaluation. Model-aided treatments required four less fungicide applications compared to routine fungicide applications. Collectively these results indicate that the severity of downy mildew is influenced substantially by the efficacy and timing of control measures applied early in the growing season.