Downy mildew (Pseudoperonospora cubensis) and powdery mildew (Podosphaera xanthii) are two of the most economically important and widespread cucurbit diseases. Disease management relies primarily on fungicide use, but frequent fungicide applications can lead to the development of resistant pathogen populations. In addition, more vegetables are being produced with organic practices, which prohibit the use of many fungicides. Incorporating biorational products into a disease management program may helpmitigate the risk of fungicide resistance development while being compatible with organic production. Field trials were conducted for two years on organically managed land in Maryland with cucumber, muskmelon, pumpkin, and butternut squash to evaluatethe efficacy of four biorational products (i.e., Actinovate AG, OxiDate, Regalia, and Serenade Soil) when applied in a rotational program with copper against foliar cucurbit diseases. Generally, all biorational treatments resulted in significantly lowerdowny and powdery mildew severity compared with the nontreated plants, but the level of disease management was not significantly different than that provided by copper alone. However, Actinovate AG, OxiDate, and Serenade Soil each improved disease management on at least one crop, as compared with copper alone. Rotational programs with biopesticides are a viable disease management option for organic production of field-grown cucurbits in Maryland.
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