Baseline sensitivity distributions of Uncinula necator to boscalid and pyraclostrobin and field performance in New York

• Author(s): Burr, J.; Riegel, D.; Wilcox, W.; Wong, Frank;
• Abstract: Boscalid (BAS 510 F) and pyraclostrobin are carboxin and QoI fungicides, respectively, in development for grapevine disease control. In 1999 and 2001, U. necator isolates collected from NY and CA were used to construct distributions of baseline sensitivities to these compounds. Single-conidiophore isolates were tested by measuring hyphal extension on fungicide treated leaf discs. For boscalid, the ED50 values of 33 CA isolates ranged from 0.0039 to 0.052 mg/L (mean=0.022 mg/L). For pyraclostrobin, ED50 values of 26 NY isolates ranged from 0.0016 to 0.010 mg/L (mean=0.0042 mg/L). In 2001, boscalid provided 99% control of cluster mildew, pyraclostrobin, 98% and the two combined (BAS 516 F) nearly 100%. In 2002, boscalid, pyraclostrobin and the combination provided 85, 82 and 100% control, respectively, in this same vineyard versus 97, 31 and 86% control, respectively, at a second site. This diminution of pyraclostrobin performance was associated with a shift in U. necator sensitivities relative to baseline values.
• Publication Date: Jun 2003
• Journal: Phytopathology