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POSTERS: Integrated pest management

Evaluation of fungicides and resistant cultivars to reduce use of chlorothalonil for powdery mildew in pumpkin and winter squash
Margaret McGrath - Cornell University. Susan Scheufele- University of Massachusetts, Beth Gugino- The Pennsylvania State University

Seven field experiments were conducted in three states to evaluate strategies to reduce use of chlorothalonil-based fungicides due to concern about potential impact on bees. A powdery mildew-resistant pumpkin cultivar (Bayhorse Gold) was less severely affected than the susceptible one (Gold Challenger) in 2016 but not in 2017 in NY and PA. Two alternative multi-site mode of action fungicides were compared to Bravo Ultrex or Weather Stik used alone and in a program with targeted fungicides (Luna Experience, Quintec, and Vivando). Efficacy similar to Bravo was achieved with Microthiol Disperss (sulfur) in most experiments and with Tritek (mineral oil) in some experiments. Based on AUDPC values, severity was suppressed on adaxial leaf surfaces by 89/95, 93/94, and 58/60%, respectively for these fungicides applied alone to the susceptible and resistant pumpkin cultivars, respectively, in NY in 2016; 92/99, 53/98, and 21/49% in PA in 2016; 97, 96, and 86% in NY in 2017; and 99, 98, and 36% in PA in 2017. Level of suppression on butternut squash cv. Atlas in 2018 was 98, 97, and 80% in NY; 100, 89, and 21% in PA, and 98, 98, and 26% in MA. Suppression on abaxial surfaces was limited, reflecting the contact activity of these fungicides. The targeted program tank-mixed with the alternatives was as effective as the one tank-mixed with Bravo in all experiments. Microthiol Disperss could be a viable alternative to Bravo for managing fungicide resistance and reducing potential negative impacts to bees while not compromising disease control especially when coupled with host resistance.