From 2009 to the current, a group of newly identified genotypes/clonal lineages/strains of the late blight pathogen were identified, with US-23 becoming most predominant in both tomato and potato production areas of the continental U.S. This presentation, developed by Amanda Gevens, Associate Professor and Extension Plant Pathologist and the University of Wisconsin–Madison, offers new information on the characterization of US-23 and other newer clonal lineages as it pertains to pathogen persistence and management. It also describes the characteristics of the most common late blight-causing strains and discusses how infections occur and spread. The presentation stresses the importance of identifying potential sources of infection and monitoring environmental factors that can promote fungal growth. More