Fundamental studies on crop disease control by spraying electrolyzed strong acid water: (2) Control of downy mildew in cucumber and occurrence of a leaf burn-like physiological disorder

摘要

Effect was investigated of spraying electrolyzed strong acid water (ESAW) obtained by electrolysis of a NaCl dilute (ca. 50 mg L~(-1)) water solution on the incidence of downy mildew (Pseudoperonospora cubensis Rostowzew)in cucumber (Cucumis sativus L. cv. Naoyoshi) grown in a plastic house, pH, free effective chlorine concentration and oxidation-reduction potential of the ESAW were 2.8. 32 ppm and 1 120 mV, respectively. Different amounts of either the ESAW (0.25, 0.5 or 1 L plant~(-1)) or well water (0.5 L plant~(-1) were sprayed onto the leaves once every third or fourth day. The incidence of downy mildew was controlled almost perfectly for the experimental period of 17 d by spraying the ESAW, regardless of the amount sprayed, while the symptom of downy mildew was observed on day 10 with well water and on day 13 with non-treated control. On day 17, the incidence was significantly reduced by spraying the ESAW (0 or 2%) as compared to both well water (48%) and non-treated control (32%). However, spraying the ESAW caused a leaf burn-like physiological disorder in some leaves after day 7, regardless of the amount sprayed. The results indicate that ESAW can be a viable alternative to some fungicides to control several crop diseases, or it can at least be effective in reducing fungicide use: however, there remains the problem of eliminating the leaf burn-like physiological disorder.