The potential of ozone nanobubbles in suppressing cucumber powdery mildew

This study evaluated the efficacy of ozone nanobubbles (O₃-NB) as a foliar treatment to suppress cucumber powdery mildew was evaluated in a controlled bioassay under optimal and suboptimal relative humidity (RH) conditions. O₃-NB solutions were generated at three concentrations (0.54 ± 0.08, 1.16 ± 0.23, and 2.08 ± 0.22 mg L^-1) and compared with oxygen nanobubbles (O₂-NB) and distilled water controls. In a 20-day growth chamber bioassay under three relative humidity conditions (≤40 %, 65-73 %, and ≥95 % RH), leaves treated with 0.5 mgL^-1 O₃-NB exhibited suppression of powdery mildew by approximately 20 ± 3.2 % and 33 ± 4.6 % compared to the control at moderate and low humidity. However, efficacy declined under high relative humidity (≥95 % RH). A 16-week hydroponic study confirmed that foliar application of O₃-NB at 0.5-2 mg L^-1 caused no adverse effects on cucumber growth, yield, or physical appearance. Although, efficacy was lower than typically reported for conventional fungicides, O₃-NB offers a potentially safer, residue-free alternative for integrated pest management programs, particularly during withholding periods where chemical fungicides cannot be used.