Emerging and re-emerging diseases of humans, animals and plants pose a significant hazard to public health and food security. With recent advances in sequencing technology, bacteriologists and virologists are now integrating high-resolution genotypic data into pathogen surveillance activities. However, the application of genomics to emerging filamentous plant pathogens has lagged. To address this, we developed a robust and rapid “field pathogenomics” strategy. We applied this method in 2013 to the wheat yellow rust pathogen Puccinia striiformis f. sp. tritici (Pst), using gene sequencing of Pst-infected wheat leaves taken directly from the field to gain insight into the population structure of a re-emerging pathogen. Our analysis uncovered a dramatic shift in the Pst population in the UK and supports the hypothesis that recent introduction of a diverse set of exotic Pst lineages may have displaced the previous population. Gene sequencing of infected host tissue can also be leveraged to assess the genotype of the host, rapidly confirming whether previously resistant wheat varieties have indeed been overcome. We have now expanded this study to analyze Pst-infected plant samples from across Europe and beyond and will provide an update on the insights we have gained regarding Pst population dynamics. Working with cross-institutional and industrial partners we are now developing this technique further to reduce cost so it can be applied routinely within the U.K. cereal disease surveillance program.