In case you missed Iowa State Extension and Outreach Corn Pathologist Alison Robertson's presentation on corn diseases at this year's Integrated Crop Management (ICM) conference, tar spot in corn has been officially confirmed, and has been identified in several counties in the state of Iowa.
In the August issue of the the American Phytopathological Society (APS) Plant Disease journal, tar spot was most recently confirmed in the states of Michigan, Iowa, Wisconsin and Florida. Corn leaves with tar-spot-like lesions were obtained in 2016 and tested. Iowa, Michigan and Wisconsin samples had identical DNA sequences, and the confirmation report is the first of its kind for the Phyllachora maydis fungus for Michigan, Iowa and Wisconsin. These states surround Indiana and Illinois, where tar spot was first reported in 2015.
Research conducted in Central and South America showed that when co-infection of P. maydis and an additional fungus, Monographella maydis, occurs, there can be significant yield loss. However, M. maydis has not yet been documented in the U.S. Tar spot in corn may currently not result in losses in grain production. However, it is unknown if this fungus can co-infect with another fungus already established in the north central region, and potentially cause yield losses. This disease, on its own, could potentially affect silage corn production when early dry-down is not desired, and could increase the potential for lodging.