Impact of Fungicide Program and Powdery Mildew Resistance in Three Varieties of Pumpkin

The effects of fungicide program and varietal resistance on the development of cucurbit powdery mildew [PM (Podosphaera xanthii)] in pumpkin (Cucurbita pepo) were tested in 2009 and 2010 in Lexington, KY. Three fungicide programs consisted of a no-fungicide control, low input (chlorothalonil), and high input (chlorothalonil alternated with myclobutanil) were applied to three varieties of pumpkin with different levels of cucurbit PM resistance. Varieties tested were Howden, Aladdin, and Camaro, which had no, moderate, and high levels of cucurbit PM resistance, respectively. There were no significant variety by fungicide program interactions for yield, number fruit per acre, and average fruit weight in both years. In 2009 and 2010, variety significantly affected yield. Yield increases corresponded to the level of cucurbit PM resistance. The high-resistance variety, Camaro, had the greatest yields in both years, while Howden, with no PM resistance, had the lowest yields. In 2010, yield significantly increased with the intensity of fungicide program. With the exception of cull percentage in 2009, there were no fungicide program by variety interactions for yield parameters. In both years, PM disease severity, characterized by the area under the disease progress curve (AUDPC), was lowest on ‘Camaro’ and highest on ‘Howden’. In 2009, unsprayed ‘Camaro’ had similar AUDPC values as ‘Aladdin’ and ‘Howden’ treated with lowor high-input fungicide programs. In 2010, unsprayed ‘Camaro’ had less disease than ‘Aladdin’ or ‘Howden’ that had received the high-intensity fungicide program. These results suggest that yields can be maintained with a minimal fungicide program when using a variety with high cucurbit PM resistant in some environments. A high-input fungicide program may be necessary to maintain yields of varieties with low cucurbit PM resistance.