Sensitivity of Sclerotinia Sclerotiorum Isolates From North Central US to Azoxystrobin and Boscalid

Azoxystrobin and boscalid are fungicides frequently used to manage diseases caused by Sclerotinia sclerotiorum (Lib.) de Bary in many broadleaf crops in North Central US. . Continued use of these compounds can induce development of fungicide-resistant strains and thus their sensitivity should be monitored periodically. The objective of this research was to generate baseline sensitivity information of S. sclerotiorum to azoxystrobin and boscalid. Salicylhydroxamic acid was toxic to ascospores even at concentrations of 0.1 ?g/ml and therefore was not used to estimate sensitivity to azoxystrobin. Azoxystrobin EC50 for ascospores and mycelium were 3.05 and 1.01 ?g/ml, respectively. Boscalid EC50 for ascospores and mycelium were 8.38 and 0.11 ?g/ml, respectively. S. sclerotiorum isolates collected before 2004 had statistically (P > 0.05) similar sensitivity to azoxystrobin but where more sensitive to boscalid (P =0.05) than isolates collected in 2014. Both fungicides continue to be effective tools to manage S. sclerotiorum.National Sclerotinia Initiative and Northern Canola Grower