LAUSR

ABSTRACT Powdery mildew is a destructive foliar disease of cucumber (Cucumis sativus L.) under greenhouse conditions. The most used methods for disease control are repeated application of fungicides and use of resistant cultivars. Development of powdery mildew isolates resistant to fungicides have reduced their efficacy. This research compared the efficacy of conventional chemical and biological fungicides as an alternative for use against powdery mildew during early plant development. The cucumber cvs. Aylar, B10 and A11 were grown in hydroponic culture. The biological fungicides (Bacillus sp. and B. subtilis), the chemical fungicide, Mancozeb® (Golsam Chemicals, Gorgan, Iran), and an essential oil extract of Froriepia subpinata Ledeb. Bail, was used as treatments against powdery mildew. Bacillus sp. and essential oil extract of Froriepia subpinata decreased severity in all cultivars compared to the control. Mancozeb® decreased severity by 26% and 25% in cvs. A11 and B10. In cv. Aylar B. subtilis decreased severity by 25%. It may be that B. subtilis can be used to protect against powdery mildew diseases in organic cultivation of cucumber under greenhouse conditions.