Activity of carbendazim, dimethachlon, iprodione, procymidone and boscalid against Sclerotinia stem rot in Jiangsu Province of China

Carbendazim (MBC) was widely used to control Sclerotinia stem rot routinely during the 1980s in China, but development of MBC resistance in the causal agent Sclerotinia sclerotiorum led to control failures of this disease. In this study it was found that the MBC resistance in S. sclerotiorum populations was widespread throughout Jiangsu Province with a resistance frequency of 29.54% in the 1786 collected isolates during the growing seasons of 2006 to 2008. The resistance frequencies differed among sampled cities, ranging from 3.1% to 54.9%. The field MBC-resistant isolates showed comparable mycelial growth, sclerotia production and pathogenicity to the wild-type sensitive isolates, which suggested that the field MBC-resistant isolates might have sufficient parasitic fitness to compete with the field MBC-sensitive isolates in the field. In the in vitro sensitivity test, boscalid showed greater activity against S. sclerotiorum than dicarboximide fungicides (dimethachlon, iprodione and procymidone). The treatment 50% boscalid (WG) 125 g a.i. ha(-1) was comparable in efficacy to the treatment 50% iprodione (WP) 600 g a.i. ha(-1), and better than other treatments of 6% dimethachlon (WP) 690 g a.i. ha(-1) and 50% procymidone (WP) 337.5 g a.i. ha(-1), whereas MBC failed to control Sclerotinia stem rot (control efficacy only 16.0%). The most active agent for controlling Sclerotinia stem rot was boscalid in our study.