In recent years, a yellow patch in turf-grass, which is probably the symptom of a new disease, has been observed in various districts of Japan. From the lesions of leaf and stem rot, binucleate Rhizoctonia was isolated and identical symptoms were reproduced in an inoculation test. The fungus did not fuse with the representative isolates of other anastomosis groups of Rhizoctonia spp. Two out of eleven isolates of this fungus developed the perfect state when the soil-on-agar culture method was applied. The perfect state of this fungus was identified as Ceratobasidium cornigerum (Bourdot) Rogers. It is proposed that this disease caused by C. cornigerum [anamorph binucleate Rhizoctonia AG-Q] would be designated as one type of ‘hagusare-byo’ of turf-grass.