In 2014 and 2018, brown rot appeared on the leaf sheaths of mioga (Zingibermioga) plants growing in Kochi, Japan. A filamentous fungus that formed pale red colonies on potato dextrose agar was isolated from the lesions and reproduced the symptoms observed on mioga plants in inoculation tests. On the basis of microscopic characters and phylogenetic analysis, the fungus was identified as Ophiosphaerellaagrostidis. This is the first report of O.agrostidis as a causal agent of a disease on mioga plants. We propose to name the new disease "leaf sheath rot" and "yosho fuhai byo" in Japanese. [ABSTRACT FROM AUTHOR]