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ARS Home » Midwest Area » East Lansing, Michigan » Sugarbeet and Bean Research » Research » Publications at this Location » Publication #344647
Title: First report of DMI insensitive Cercospora beticola on sugar beet in Ontario, Canada

Author
item TRUEMAN, CHERYL - University Of Guelph
item ROSENZWEIG, NOAH - Michigan State University
item SOMOHANO, PAULA - Michigan State University
item Hanson, Linda

Submitted to: New Disease Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2017
Publication Date: 11/26/2017
Citation: Trueman, C.L., Rosenzweig, N., Somohano, P., Hanson, L.E. 2017. First report of DMI insensitive Cercospora beticola on sugar beet in Ontario, Canada. New Disease Reports. 36:20.

Interpretive Summary: Cercospora leaf spot (CLS) has been a problem in Ontario Canada and worldwide. Management includes host resistance and cultural practices, but fungicides are generally necessary for economic control. One class that has been used for disease management is the demethylase inhibitor (DMI) class of fungicides. The first of these was registered for sugar beet in Onatario in 2006, and now these fungicides are widely used. During an annual screening for fungicide sensitivity in the region, strains of the fungal pathogen Cercospora beticola (cause of CLS) were collected from twelve commercial sites in the major sugar beet growing region in Ontario, Canada during September 2016. CLS sampled had severity from approximately 40 to 70% leaf area affected. At least one DMI fungicide had been applied during the 2016 growing season at sites for which records were available. Approximately 30 isolates were screened in two lab assays against the DMI fungicides. Between 42 and 57% of the isolates were classified as insensitive or resistant to the fungicides. This is the first report of DMI insensitive C. beticola in Canada. Resistance has been reported in Europe and the Red River Valley of the USA. This resistance to DMI fungicides poses a particular challenge for sugar beet production in Ontario due to favorable conditions for disease development and limited availability of alternative control measures.

Technical Abstract: Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is an economically important foliar disease of sugar beet in Ontario, Canada and worldwide. Fungicides are an important tool in the control of CLS. The first demethylation inhibitor (DMI) fungicide for sugar beet was registered in Canada in 2006, with five now available for use. As part of an annual fungicide sensitivity monitoring program, leaves with CLS symptoms were collected from twelve commercial sites in September 2016. The sites were in the major sugar beet growing region in Ontario, Canada in Kent and Lambton Counties. Disease severity at the sites ranged from approximately 40 to 70% leaf area affected. At least one DMI fungicide had been applied during the 2016 growing season at sites for which records were available. Isolate sensitivity expressed in mg/L was determined by the effective control for 50% of germinating conidia (EC50) on water agar amended with technical grade DMI fungicides at 0, 0.01, 0.1, 1, 10, or 100 mg/L using a the spiral gradient dilution method and a relative growth assay. Approximately 30 isolates were screened against the five DMI fungicides. The mean EC50 values ranged from 38 to 66 for all the fungicides, well above the 1 mg/L classified as resistance, with between 42 and 57% of the isolates classified as insensitive or resistant to the fungicides. This is the first report of DMI insensitive C. beticola in Canada, similar to what has been found in Europe and the Red River Valley of the USA. This resistance to DMI fungicides poses a particular challenge for sugar beet production in Ontario due to favorable conditions for disease development and limited availability of alternative control measures.