The causal agent of a patch disease of buffalo grass (syn. St Augustine grass) is determined and described as a new species, Gaeumannomyces wongoonoo sp. nov. Glasshouse experiments have shown that it is pathogenic to buffalo grass (cultivar ST 1191) but not to maize or wheat. The pathogen is different to the varieties of G. graminis in having shorter ascospores (36–75 μm) and producing numerous perithecia readily on malt extract and potato dextrose agars. The disease is named ‘wongoonoo patch’ to distinguish it from take-all patch of turf grasses caused by G. graminis.