1998 Volume 36 Issue 3 Pages 137-143
The effects of spraying water with different hydrogen-ion concentration exponents (pHs) and free effective chlorine concentrations (ECCs) on the incidence of powdery mildew (Sphaerotheca fuliginea Pollacci) on leaves of cucumber (Cucumis sativus L. cv. Shapu 7) grown in a plastic house were investigated as a fundamental research for the establishment of a crop disease control system with electrolyzed strong acid water. pH-regulated waters (pH: 2.0, 2.3 or 2.6; ECC : 0 ppm ; oxidation-reduction potential (ORP) : almost constant at 510 mV), ECC-regulated waters (ECC : 30, 40 or 50 ppm ; pH : 2.3 ; ORP : almost constant at 1 170 mV), or well water (pH: 7.8, ECC : 0 ppm, ORP : 460 mV) were sprayed, 4 times in 9 days, onto the leaves once every third day. The incidence of powdery mildew on cucumber leaves showed a tendency to decrease with decreasing pH or with increasing ECC of the sprayed water over the 12 days of observation. Water with a pH of 2.0 suppressed the incidence significantly at the 5% level against water with a pH of 2.6 and well water on day 12, which is 3 days after the last spray. Water with an ECC of 50 ppm suppressed the incidence significantly at the 5% level against water with an ECC of 30 ppm and well water on day 12. These results indicate that pH lower than a certain level can be a factor independently capable of controlling powdery mildew on cucumber leaves in spraying electrolyzed strong acid water, and that ECC higher than a certain level under a low pH can be a primary factor capable of controlling it.
