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ARS Home » Midwest Area » East Lansing, Michigan » Sugarbeet and Bean Research » Research » Publications at this Location » Publication #316248
Title: Response of Alternaria spp. from sugar beet leaf spots to fungicides

Author
item WU, HANG HANG - Michigan State University
item JIANG, QIANWEI - Michigan State University
item KIRK, W - Michigan State University
item Hanson, Linda

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: Wu, H., Jiang, Q., Kirk, W.W., Hanson, L.E. 2015. Response of Alternaria spp. from sugar beet leaf spots to fungicides. [CD-ROM] 2014 Annual Beet Sugar Development Foundation Research Report. Denver, Colorado: Beet Sugar Development Foundation.

Interpretive Summary:

Technical Abstract: Leaf spot caused in sugar beet by Alternaria species has been a minor foliar disease issue in the United States. Recently in Michigan and other growing regions an increasing incidence of Alternaria leaf spot has been observed and without evidence of predisposing plant yellowing. One possible reason for increased disease in the United States is that the pathogen has been inhibited previously by fungicides used for management of other foliar diseases. As fungicide resistance has been reported in Alternaria species on other crops, there is a possibility that fungicide resistance could be making some Alternaria more able to colonize beet tissue despite the ongoing fungicide usage. The current work was to test for the possibility of resistance to commonly used foliar fungicides in sugar beet to begin to assess the potential for fungicide resistance to be a factor in increased disease incidence in Michigan. Thirteen isolates of Alternaria spp. collected from sugar beet were used in testing. This included isolates collected from 2013 leaves and eight isolates from the SBRU culture collection. All isolates grew well on the spiral gradient plate control. All isolates tested showed tolerance to triphenyltin with EC50 values varying from 2-4 ppm, but all greater than 1 ppm and all Alternaria isolates showed high levels of resistance to the other fungicides tested, with little or no growth inhibition at the highest concentration of fungicide tested (100 ppm) for fungicides from three different chemical classes. The finding of high levels of resistance to the majority of fungicides tested and moderate tolerance to triphenyltin hydroxide, indicates that fungicide resistance is present in the Alternaria spp. associated with sugar beet and that tolerance has been present for several years. Several of the fungicides currently used for leaf spot management are expected to have little or no impact on growth of Alternaria spp. found on sugar beet.