Abstract Powdery mildew caused by Podosphaera xanthii has affected watermelon in the southeastern United States since the late 1990's. Because this fungus has become resistant to fungicides in FRAC Groups 1 and 11, fungicides in FRAC Groups 3, 7, 9, 12, 13, and U6 were tested on seedless watermelon for their ability to reduce powdery mildew on foliage and prevent yield loss. Nine powdery mildew-specific fungicides were applied three times in alternation with chlorothalonil, which was applied three times in 2013 and four times in 2014. Control treatments included water and chlorothalonil applied every other week. In both years, four fungicide treatments, chlorothalonil alternated with triflumizole, fluopyram + tebuconazole, quinoxyfen, or both cyflufenamid and quinoxyfen reduced leaf area covered with powdery mildew compared to both control treatments. Chlorothalonil alternated with cyflufenamid and quinoxyfen was significantly more effective on lower leaf surfaces than all other treatments. Chlorothalonil alternated with tebuconazole did not differ from chlorothalonil applied every other week. All 10 fungicide treatments increased the number and weight of marketable-sized fruit in both years compared to the water control treatment. Fungicide active ingredients in FRAC Groups 3, 7, 13, and U6 consistently reduced the severity of powdery mildew on seedless watermelon.