Management of powdery mildew, caused by Erysiphe cruciferarum, on wasabi (Wasabia japonica) plants in British Columbia
2021
Betz, E.C. | Punja, Z.K.
Powdery mildew on wasabi (Wasabia japonica (Miq.) Matsumura)plants reduces photosynthesis and severe infections can result in chlorosis and defoliation, resulting in reduced yields. Erysiphe cruciferarum Opiz ex L. Junell was confirmed as the causal agent using sequence analysis of the ITS1-5.8 S-ITS2 region, along with conidial and conidiophore morphology. To evaluate reduced-risk management options, the efficacy of four commercially available products was assessed over three separate trials conducted in a commercial wasabi greenhouse in British Columbia. The products tested included two biological pesticides, Bacillus subtilis strain QST 713 (formulated as Rhapsody ASO), and Streptomyces lydicus strain WYEC 108 (formulated as Actinovate SP), as well as a copper-based fungicide, Cueva, and a plant formulated extract, Regalia Maxx (from Reynoutria sachalinensis). Treatments were applied at two-week intervals over 10–12 weeks starting with onset of disease symptoms. Natural infection by E. cruciferarum was allowed to progress on the plants during the trials. Leaves were assessed for powdery mildew biweekly based on percentage of leaf surface infected, which was then converted to area under the disease progress curve (AUDPC) for each treatment. Five to six applications of Cueva and Regalia significantly (p < 0.05) reduced the progression of powdery mildew in all trials. Rhapsody also reduced disease progression in some trials, but to a lesser extent. Actinovate was not effective. These results provide producers of wasabi with reduced-risk options for management of powdery mildew.
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