Monitoring the sensitivity of Sclerotinia sclerotiorum to fungicides

Abstract: Sclerotinia sclerotiorum isolates from oilseed rape are monitored every year for fungicide resistance. In the past, the use of carbendazim was very popular and led to a widespread resistance among S. sclerotiorum populations, especially in the oilseed rape cropping areas. Regarding dicarboximides (eg iprodione, vinclozoline or procymidone), very few resistant isolates have been detected in several French regions, not affecting field efficacy. These fungicides are no longer registered in France. For two years, new fungicides belonging to carboxamides and the DMI families have been registered to control this disease. Thus, determining S. sclerotiorum baseline sensitivity to these new compounds was necessary to manage sustainable use. A method based on mycelial growth on synthetic agar medium amended with a concentration of 2 mg/l was developed for boscalid, prothioconazole and metconazole. The methods allowed us to determine the sensitivity to boscalid of around 1400 field isolates; no resistance to boscalid was detected in 2007. The method was less reliable for DMI compounds.