Cercospora leaf spot (CLS), caused by Cercospora beticola (Sacc.), is the most serious foliar disease of sugarbeet (Beta vulgaris L.) worldwide. Timely fungicide application is one of the most effective tools used to manage this disease. However, this strategy has been less effective because resistance has been reported in C. beticola to several classes of fungicides including benzimidazoles, organotin and demethylation inhibitors (DMIs). Thus knowledge of the interaction of C. beticola in Michigan with various fungicides is essential for making management decisions. A study has been conducted to survey the Great Lakes sugarbeet growing region for C. beticola isolates with sensitivity to various fungicides in use in the area. Results showed that most C. beticola isolates (>85%) tested were sensitive to DMI and organotin fungicides during the study (from 2012 to 2014) with EC50 values of less than 1 and 5 ppm respectively. Monitoring for the mutations in commercial fields indicated that resistant mutations were widespread in both Michigan and Ontario sugarbeet production areas. This data will direct the development of effective recommendations specific to production areas.
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