Collar rot disease of Amorphophallus paeoniifolius caused by Sclerotium rolfsii is an important disease existing in all Amorphophallus growing areas. The pathogen propagules present in soil and planting material form key basis of inoculum. This study presents the aptness of D1/D2 domain of large-subunit ribosomal DNA (rDNA-LSU) for PCR based detection of S. rolfsii. The detection limit of conventional PCR was 10 pg and that of nested PCR was 100 fg of pathogen DNA. The designed primer was found to be highly specific and could be used for accurate identification of pathogen up to the species level. The protocol was standardized for detection of the pathogen in artificially and naturally infected field samples. The PCR-based method developed here could be used for both disease diagnosis and pathogen monitoring, as well as in guiding plant disease management.