Integrated Control of Black Rot Disease of Wasabi, Caused by Phoma Wasabiae

Abstract

Soaking with difenoconazole, thiabendazole, benomyl, and polyoxin eliminated the pathogen as an initial inoculum source in rhizome-tillers and root-plantlets of wasabi. The effective period was 2, 4, 8, and 10h, respectively, for difenoconazole, thiabendazole, benomyl, and polyoxin. Because thiabendazole and difenoconazole caused injury to wasabi tillers, only benomyl was used to control disease in tillers in the field. When plots were covered with PE sheets, leaf spot disease of wasabi was significantly reduced. The average disease incidence of black rot was reduced from 90% to 5.9%. The pathogen was effectively prevented by benomyl from spreading from the parent rhizomes to tillers in the field. Treating wasabi tillers only with benomyl, however, did not significantly reduce the disease incidence on wasabi leaves or petioles. In contrast, the tillers from rhizomes treated with benomyl and covered with a polyethylene sheet on the cultivated plot significantly reduced the disease severity on wasabi rhizomes, petioles and leaves. The treatments reduced disease severity from 75% to 12.5% in rhizomes, from 73.5% to 37.5% on petioles, and from 72.6% to 33.5% on leaves of wasabi. The results of this study suggest that using pathogen-free plantlets and preventing secondary infection with polyethylene cover could be effective in controlling black rot disease of wasabi in the field.