Root rot of Wasabia japonica caused by Nectria haematococca was first observed in Fuxing District of Taoyuan City in July, 2015. Diseased plants showed stem and rhizome rot, and subsequently leaves wilted and the plants died. Nectria haematococca was isolated from infected tissues, and the disease was reproduced in the lab by inoculation of the roots with a mycelial and spore suspension of the pure pathogen culture. After inoculation, 55.6% of plants developed the same stem and rhizome rot symptoms, and the pathogen was reisolated from inoculated plants to complete the pathogenicity test. Amendment with the pesticides Thiabendazole, Tridemorph, Benomyl, or Carbendazim, or essential oils of Cinnamomum osmophloeum, Cymbopogon citrates and Cinnamomum camphora leaves into potato dextrose agar medium, effectively inhibited mycelial growth of N. haematococca.