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ARS Home » Midwest Area » East Lansing, Michigan » Sugarbeet and Bean Research » Research » Publications at this Location » Publication #316247

Title: An examination of fungicide sensitivity of Cercospora beticola in Michigan and Ontario sugarbeet (Beta vulgaris) (2014)

Author
item JIANG, Q - Michigan State University
item Hanson, Linda
item KIRK, W - Michigan State University
item ROSENZWEIG, N - Michigan State University
item SOMOHANO, P - Michigan State University

Submitted to: Annual Beet Sugar Development Foundation Research Report
Publication Type: Research Notes
Publication Acceptance Date: 4/15/2015
Publication Date: 6/1/2015
Citation: Jiang, Q.W., Hanson, L.E., Kirk, W.W., Rosenzweig, N., Somohano, P. 2015. An examination of fungicide sensitivity of Cercospora beticola in Michigan and Ontario sugarbeet (Beta vulgaris) (2014). [CD-ROM] 2014 Annual Beet Sugar Development Foundation Research Report. Denver, Colorado: Beet Sugar Development Foundation.

Interpretive Summary:

Technical Abstract: Leaf spot caused by Cercospora beticola Sacc. is the major foliar disease of sugarbeet in Michigan. Fungicide applications are one of the most important tools in managing this disease. However, fungicide resistance has developed in C. beticola to several classes of fungicides. To look for the levels of fungicide sensitivity in C. beticola in Michigan there has been an ongoing survey effort screening for reduced sensitivity to a number of fungicides in the region to track changes and assist in making management decisions. Using a spiral gradient dilution method, 82 % of 142 isolates tested in 2014 were sensitive to triphenyltin hydroxide (TPTH) with EC50 values of less than 1 parts per million (ppm). While the majority of isolates were sensitive, this was the first time in three years of screening that any isolates had EC50 values greater than 5 ppm. There were only four isolates in the category, but this raises concerns about the potential for increased tolerance to this fungicide in C. beticola in Michigan. Five fungicides in the DMI fungicide class were screened for efficacy on C. beticola isolates. The majority of isolates tested were sensitive with EC50 values of less than 5 ppm. The percentage of isolates with EC50 values greater than 1 ppm varied for the different fungicides and has increased over the past 3 years, indicating a shift toward reduced sensitivity in the region. A small portion of isolates had EC50 values of greater than 10 ppm which may raise concern because as this level may lead to reduced field efficacy of the fungicides. Two other fungicides were screened using a PCR-RFLP test. Based on this 98.8% of composite samples (5 lesions per sample) showed evidence of resistance to strobilurin fungicides and 75.8% of the composite samples included the resistant type for benzimidazoles, with 58.2% having only the resistant type and the rest a mixture of resistant and sensitive material. This indicates that both resistance to both fungicide classes is widespread in the Michigan Sugar growing region.