Identification and management of wasabi pathogens in British Columbia

Wasabi (Wasabia japonica) plants in British Columbia are grown in moist conditions ideal for pathogens, and therefore, are prone to various diseases. Over 3 years, seven wasabi greenhouses were surveyed for pathogens. Prevalence and severity of diseases were documented. Pathogenic species including Phoma wasabiae (Leptosphaeria biglobosa), Botrytis cinerea, and Erysiphe cruciferarum were found in multiple greenhouses. A new disease of wasabi with symptoms of vascular blackening and wilt was discovered. Using morphological and molecular techniques, the causal organism was identified as Verticillium isaacii. Powdery mildew of wasabi caused by E. cruciferarum was prevalent in half the greenhouses surveyed. In order to evaluate management options for powdery mildew, 4 commercially available products, Actinovate®, Cueva®, Rhapsody®, and Regalia® were applied biweekly onto greenhouse plants. Both Cueva® and Regalia® significantly reduced the progression of powdery mildew on wasabi plants.