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24 POTATO GROWER | MAY 2020 Diggin' In Diggin' In Quantifying control efficacy of early blight fungicides The Right Combination Foliar fungicides continue to be the primary means for the management of early blight caused by Alternaria solani in potatoes. Potato growers in North Dakota and Minnesota have been concerned that standard fungicides applied alone do not necessarily guarantee adequate protection against early blight epidemics in growing seasons conducive to disease development. High disease pressure based on yearly environmental fluctuations is one reason that growers have incorporated more expensive single- site specialty fungicides into foliar disease management programs. The goal of a recent North Dakota State University study was to compare early blight control resulting from fungicide programs using solely standard protectant fungicides when compared to programs which incorporated specialty fungicides. whaT we DiD Twelve field trials were conducted in North Dakota and Minnesota from 2003 to 2014. Early blight severity was visually estimated on a weekly basis for 11 weeks beginning five weeks after planting. Specialty fungicides were separated into two groups based on mode of action. QoI (quinone outside-inhibitor) and SDHI (succinate dehydrogenase inhibiting) fungicides were applied in rotation with standard protectant fungicides. We compared early blight severity at two crop growth stages, tuber initiation to early bulking (weeks 7 to 9) and late bulking to tuber maturation (weeks 10 to 11). We also compared total yield in response to standard and specialty fungicides using network meta-analytic models. whaT we leaRneD In this study, there was a significant difference in overall efficacy and FUNGICIDES | By S. K. R. Yellareddygari, Neil C. Gudmestad, Raymond J. Taylor & Julie S. Pasche Year Specialty Fungicide Group 1 (active ingredient) Specialty Fungicide Group 2 (active ingredient) Standard Fungicide (active ingredient) 2003 Pyraclostrobin+Mancozeb Boscalid+Mancozeb Chlorothalonil 2004 Famoxadone+Mancozeb Boscalid+Chlorothalonil Mancozeb 2005 Pyraclostrobin+Pyremethanil+Chlorothalonil Boscalid+Famoxadone+Chlorothalonil Mancozeb 2006 Famoxadone+Pyremethanil+Mancozeb Boscalid+Pyraclostrobin+Chlorothalonil Mancozeb 2007 Pyraclostrobin+Pyremethanil+Chlorothalonil Boscalid+Famoxadone+Mancozeb Chlorothalonil 2008 Pyraclostrobin+Pyremethanil+Mancozeb Boscalid+Famoxadone+Mancozeb Mancozeb 2009 Pyraclostrobin+Pyremethanil+Mancozeb Difenoconazole+Mandipropamid+Chlorothalonil Chlorothalonil 2010 Fenamidone+Pyremethanil+Chlorothalonil Difenoconazole+Mandipropamid+Chlorothalonil Mancozeb 2011 Fenamidone+Pyremethanil+Chlorothalonil Difenoconazole+Mandipropamid+Chlorothalonil Chlorothalonil 2012 Fenamidone+Pyremethanil+Chlorothalonil Boscalid+Famoxadone+Mancozeb Chlorothalonil 2013 Fenamidone+Pyremethanil+Chlorothalonil Boscalid+Pyraclostrobin+Chlorothalonil Chlorothalonil 2014 Fenamidone+Pyremethanil+Chlorothalonil Fluopyram+Pyremethanil+Mancozeb Mancozeb Treatments evaluated in a network meta-analysis of 12 field trials conducted in North Dakota and Minnesota from 2003 to 2014 Positive sign (+) indicates alternation with fungicide with different active ingredient. A non-treated treatment was included for all trials. Overall, 10 fungicide applications were performed during each potato-growing season. Each specialty group fungicide regime included a total of three applications of a specialty single-site mode-of-action fungicide in rotation with seven standard protectant fungicide applications.