Fungicide Sensitivity and Evaluation of Effective Fungicides against Cercospora cf. citrullina, the Causal Agent of Watermelon Leaf Spot

Leaf spot caused by Cercospora cf. citrullina has recently been observed in greenhouse-grown watermelon in Korea, where high humidity conditions favor fungal disease development. This study evaluated the fungicide sensitivity of six representative isolates collected from two greenhouse farms and assessed the in vivo efficacy of selected fungicides. In vitro assays using the agar dilution method revealed significant differences among fungicides. Mancozeb completely inhibited mycelial growth of all isolates, while fludioxonil exhibited strong inhibition, although one isolate (SYP-1772) showed reduced sensitivity. Tebuconazole and pyraclostrobin demonstrated moderate activity, whereas boscalid and benomyl were less effective. In wounded-leaf inoculation assays, both mancozeb and fludioxonil significantly reduced disease severity compared with the untreated control. Mancozeb showed consistent preventive activity, whereas fludioxonil demonstrated higher curative efficacy when applied after inoculation. These findings provide baseline fungicide sensitivity data and practical information for selecting effective chemical control options for managing watermelon leaf spot under greenhouse conditions.