Sugarbeets account for 55 to 60% of U.S. sugar production. Cercospora leaf spot (CLS), primarily caused by the fungal pathogen Cercospora beticola, is a major foliar disease of sugarbeet. Since leaf tissue is a primary site of pathogen survival between growing seasons, management strategies were evaluated to reduce this source of inoculum. Fall- and spring-applied treatments were evaluated over three years at two locations. Treatments included a non-treated control, a propane-fueled heat treatment, and a desiccant application seven days pre-harvest compared to tilling immediately post-harvest. The fall-applied heat treatment significantly reduced lesion sporulation and C. beticola isolation in at-harvest samples (P < 0.05) as well as detectable sporulation for up to 70- or 90-days post-harvest (P < 0.05). Both fall- and spring-applied heat treatments reduced CLS area under the disease progress curve in the growing season after treatment (P < 0.05).Fungicide resistance is a major concern due to the frequent applications necessary to control multiple infection cycles of CLS each season and the importance of single-site fungicides. Reduced sensitivity has been observed for C. beticola to multiple fungicide groups, including quinone outside inhibitors. Programs were tested to minimize C. beticola pyraclostrobin resistance development and maximize management of CLS. In 2019 and 2020, rotation and tank-mixture programs integrating pyraclostrobin with mancozeb treatments were evaluated in field studies. For all programs incorporating pyraclostrobin, distributions of C. beticola pyraclostrobin sensitivities were not significantly different from each other but differed from the non-treated control (P < 0.05). No additional CLS control, yield, or sugar benefits were observed for programs using pyraclostrobin. Monitoring the development of fungicide resistance in the region is important for making management decisions. In 2021 and 2022, the distribution of in vitro fungicide sensitivity was determined in Michigan C. beticola isolates and mutations associated with resistance to various fungicide groups were assessed. High levels of resistance to prothioconazole and pyraclostrobin were observed for C. beticola isolates collected from commercial sugarbeet fields. Tested isolates were most sensitive to difenoconazole, fenbuconazole, and triphenyltin hydroxide. The number of fungicide group applications affected isolate sensitivity to thiophanate-methyl and prothioconazole (P < 0.05). Many triazoles in this study possessed cross resistance with other DMI fungicides. This study found the E198A mutation was accurate in predicting resistance to thiophanate-methyl, while the G143A and Glu169 mutations were not sufficient to forecast resistance to pyraclostrobin and all triazole active ingredients, respectively. Current CLS prediction models used for fungicide application timing do not consider the presence of C. beticola spores. CLS forecasting could benefit from the addition of aerial spore factors. In 2019-2022, eight site-years of aerial spore and environmental data were collected from Michigan and Ontario. Initial correlation and logistic regression analyses found duration of leaf wetness, air temperature, and wind speed were able to predict the risk of elevated Cercospora spore concentrations with 67.9% accuracy. In 2022 and 2023, a limited set of thresholds for a selected model were tested for fungicide application timing. Two models resulted in CLS, yield, and sugar metrics comparable to the grower standard despite one less fungicide application. In additional training analysis, an ensemble model included leaf wetness, air temperature, relative humidity, and wind speed variables with a testing accuracy of 73.2%. These studies aimed to develop integrated CLS management options to improve sugarbeet production sustainability and profitability.
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