Efficacy of Fungicides, Inducing Biochemical Defense and Role of Weather Parameters on Development of Cucumber Powdery Mildew

Abstract

Cucurbit powdery mildew, caused by Podosphaera xanthii (Schltdl.) U. Braun & S. Takam., is a serious threat to cucumber (Cucumis sativus L.) production worldwide and can cause 50-70% yield losses in affected environments. This study evaluated the efficacy of systemic fungicides for managing powdery mildew. The systemic fungicides propiconazole, azoxystrobin, pyroclostrobin, difenoconazole, tebuconazole and hexaconazole were applied at disease onset, and the subsequent spray was administered at a 10-day interval. The significantly lowest powdery mildew per cent disease intensity and the highest per cent disease reduction over the control (30.54 and 56.07, respectively), maximum fruit yield (152.64 q/ha) and lowest AUDPC (582.29) were recorded with propiconazole 25% EC, which was statistically comparable to azoxystrobin 23% SC (34.18 PDI, 50.84% disease reduction over the control, 151.30 q/ha yield and 637.23 AUDPC). All treatments were effective in enhancing and sustaining chlorophyll content, indicating improved photosynthetic efficiency. Compared with the control, all treatments exhibited higher peroxidase, polyphenol oxidase and chitinase activities. Powdery mildew was observed in the 37th SMW with a PDI of 9.86% and peaked in the 41st SMW with 76.26% PDI. Powdery mildew showed positive correlations with maximum temperature and sunshine hours, and negative correlations with minimum temperature, morning humidity, evening humidity and rainfall.