Limiting Fungal Foliar Diseases on Carrots for Organic and Conventional Markets

Abstract

Michigan ranks fourth in carrot production for the combined fresh and processing markets. Fungal foliar diseases caused by Alternaria dauci and Cercospora carotae occur annually in the state, causing blighted and weakened leaves and petioles. Our objective was to update current disease management strategies for both organic and conventional production by testing Organic Materials Review Institute (OMRI)–approved and conventional fungicides against C. carotae and A. dauci. Field trials conducted in 2015 and 2016 found that the copper-based fungicides (copper hydroxide and copper hydroxide/copper oxychloride) were the only OMRI-approved products that, as indicated by relative area under the disease progress curve (rAUDPC) data, consistently limited foliar blight. In field trials of conventional fungicides, all treatments limited symptomatic foliar area and protected petiole health compared with the control in both years with one exception: propiconazole was similar to the control in 2016 for petiole health and in 2015 for rAUDPC values. During 2016 when disease pressure was high, pyraclostrobin/fluxapyroxad outperformed iprodione, pyraclostrobin, azoxystrobin/propiconazole, and cyprodinil/fludioxonil for the control of foliar blight. Yields differed significantly among conventional treatments only in 2016. In plots sprayed with pyraclostrobin/boscalid, pyraclostrobin/fluxapyroxad, chlorothalonil, and boscalid had higher yields than penthiopyrad, iprodione, and propiconazole. These results can contribute to management strategies for C. carotae and A. dauci in organic or conventional production systems.