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POSTERS: Chemical control

The effects of reducing chlorothalonil use in fungicide spray programs for melon diseases
Jake Jones - University of Maryland, College Park. Kathryne Everts- University of Maryland, College Park

Fungicides are applied to nearly 80% of U.S. melon acreage to manage the numerous foliar and fruit diseases that threaten yield. Chlorothalonil (ex.Bravo) is the most widely used fungicide but has been associated with negative effects on human and bee health. We designed alternative fungicide spray programs to examine impact of reducing use of Bravo on watermelon, muskmelon, and honeydew melon in 2016, 2017, and 2018. Bravo was replaced in the tank-mix of weekly sprays of targeted fungicides, with either a polyoxin D zinc salt (Oso) or an extract of Reynoutria sachalinensis (Regalia). Powdery mildew (PM-Podosphaera xanthii) and gummy stem blight (GSB-Stagonosporopsis spp.) were the most prevalent diseases to occur in the three years. Where Bravo was replaced by Oso alternated with Regalia within a program, PM severity was not significantly different (p=0.08, Wilcoxon Test) than where Bravo was used (2% and 5%, respectively compared with 35% severity in the untreated control in honeydew melon in 2018). Similarly, for GSB in muskmelon in 2017, the program with Oso and Regalia and the program with Bravo resulted in statistically similar severities (p=0.20, Wilcoxon Test) 8% and 7%, respectively, compared to the untreated control at 37%. Bravo, Regalia, and Oso were also applied as standalone treatments and all had higher disease severity than the Bravo tank mixed with targeted fungicides (p<0.05, Wilcoxon Test). Therefore, replacement of Bravo is possible, without loss of efficacy, when Oso is alternated with Regalia as a tank-mix with targeted fungicides to manage PM and GSB.