The family Pyriculariaceae includes several agronomically important pathogens of primarily grass hosts. The best studied example, Pyricularia oryzae, includes several divergent lineages including the causal agents of rice blast, wheat blast, and gray leaf spot of several turfgrass species. While other members of this genus are host specific, artificial inoculation and other studies have demonstrated cross-infectivity on a wider variety of grass species than typically found in naturally occurring epidemics, creating the potential for pathogen co-occurrence, genetic exchange, and adaptation to novel hosts. Microstegium vimineum is an invasive annual C4 grass that has colonized many forests in the Eastern USA. In the summer of 2018, a Pyricularia-like species was isolated from foliar lesions on M. vimineum in Indiana, where we are studying M. vimineum as a model for the emergence and accumulation of pathogens on non-native species. Symptoms included diamond to elongated, foliar, water-soaked, gray to olivaceous lesions with necrotic borders; some lesions underwent further secondary development and resembled blast-like symptoms on the leaf. Fungal isolates had pyriform, two to three-celled conidia born sympodially on erect conidiophores. A blast search of Genbank of ITS sequences revealed no results with greater than 95% nucleotide identity. Our preliminary results indicate these are isolates of a novel species within the Pyriculariaceae causing a new disease of M. vimineum in Indiana. We hypothesize that this represents adaptation to a new host by a pathogen of a native grass.