Phytophthora infestans, entered the shores of Ireland in 1845 and caused a potato “plague” that devastated the crop. No one knew where it came from or how the plant disease could be controlled. In Ireland, the pathogen left devastation in its wake: a country of eight million lost one quarter of its population to death and emigration. The population of Ireland would never rebound. We used natural history collections and herbarium specimens to track this plant killer. We identified the famine lineage in historic specimens, refuting a previous misidentification of the ancestral strain. The FAM-1 lineage caused historic outbreaks in both US in 1843 and Europe in 1845. Surprisingly, FAM-1 was present globally for over 140 years. Herbaria specimens sampled over space and time allowed her to track the historic lineage and its spread through British colonization and trade routes globally. Population genomics data from historic P. infestans also linked the ancestral FAM-1 lineage to a sister species, P. andina that is only found in the Andes. My talk traces the evolution of scientific thinking about the underlying causes of late blight before delving into my own research journey, which culminated in the genome sequencing of historic pathogen DNA to establish where the pathogen that caused the potato blight originated. A T-BAS phylogeny of Phytophthora has been released as a community resource tool for identification and phylogenetic tracking of SSR lineages of P infestans and emergent new Phytophthora species. We have maintained a surveillance and mapping system (USAblight.org) to report modern disease outbreaks in North America and have developed new diagnostic technologies that combine LAMP sensors, bioinformatics, and geospatial surveillance tools to observe, contain and limit outbreaks of this and other important Phytophthora diseases.