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Evaluation of fungicides for control of Ceratocystis fimbriata and Rhizopus stolonifer on sweetpotato

Hunter Collins: North Carolina State University

<div>North Carolina is the number one sweetpotato producer in the United States, over 90,000 acres are harvested every year in the state, and approximately 30% of the crop is exported. <em>Ceratocystis fimbriata</em>, the causal agent of black rot, and <em>Rhizopus stolonifer, </em>the causal agent for Rhizopus soft rot, are economically important postharvest pathogens of sweetpotato. However, few active ingredients are labeled for disease control in sweetpotato, even fewer products are allowed for use in roots for export, and little is known regarding the efficacy of products. To identify fungicides that reduce disease, sweetpotatoes were wounded and then inoculated with either <em>R. stolonifer</em> or <em>C. fimbriata</em>. Fungicide treatments were applied to roots as sprays or dips, roots were incubated at 24°C for 29 days for black rot and 26°C for 21 days for Rhizopus, and rated for disease incidence at 14, 21, and 29 days for black rot, and 7, 14, and 21 days for Rhizopus. Our results revealed that Mertect 340F as a dip or spray (thiabendazole), and sprays of Mentor (propiconazole), Orius 3.6F (tebuconazole), Chairman (fludioxonil + propiconazole), and Stadium (azoxystrobin + fludioxonil + difenoconazole) provided significant reductions in black rot incidence. While Chairman, Orius, and Stadium provided significant reductions in Rhizopus incidence. Our findings are a first step towards expanding the number of registered products for postharvest disease control in sweetpotato.</div>