Protective and curative effects of foliar-spray Fenton solutions against cucumber (Cucumis sativus, L.) powdery mildew

Abstract

Various Fenton solutions have been developed for advanced oxidation processes in wastewater treatment. In this study, conventional Fenton solutions such as hydrogen peroxide (HOOH) + Fe2+ (Mix 1) or HOOH + Fe3+ (Mix 2), and a new type of solution, HOOH + Fe3+ + oxalic acid (Mix 3), were used as foliar sprays against powdery mildew on cucumber caused by Sphaerotheca fuliginea. Three Fenton solutions, plus a fungicide, fenarimol, were used to cure and/or protect the plant from powdery mildew under greenhouse conditions. Determination of the ·OH photoformation rate of these Fenton solutions revealed that Mix 3 had a photoformation rate 3.6 - 4.3 times higher than those of Mix 1 and 2. Application of fenarimol and Mix 3 to each plant once a week for three weeks resulted in high curative effects for already–diseased plants. Double spraying with fenarimol and the Mix 3 solutions 1–7 days before S. fuliginea inoculation resulted in the protective effects continuing for up to 20 days after spraying. When the disease reemerged at 20 days post inoculation, one reapplication of the spray suppressed the disease for another 7 days. Overall, fenarimol and Mix 3 were most effective for both the protection and suppression of the disease. These results implied that Mix 3 had fungicidal effects similar to fenarimol; therefore, the use of a Fenton solution such as Mix 3 may offer new possibilities for disease control.