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Soybean Cultivars and Fungicide Responses to Frogeye Leaf Spot – Ten Years of Field Data
W. J. JORDAN (1), H. M. Kelly (1), M. A. Newman (1). (1) University of Tennessee, Jackson, TN, U.S.A.

Frogeye leaf spot (FLS) caused by <i>Cercospora sojina</i> Hara can be a devastating foliar disease in many part of the United States. Reductions in yields of 20-40% are not uncommon under environmental conditions that promote growth and sporulation of the fungus. Fungicide spray regimes and cultivar selection have been used to combat the impact of the disease by many producers. Over 600 different commercially available cultivars were evaluated in Milan, TN from 2003 through 2013. Cultivars tested included maturity groups III, IV, and V. All plots were sprayed at the R3 growth stage with a commercially available fungicide, and were visually rating for FLS lesions at the R5-R6 growth stage. Yield was collected for each of the sprayed and unsprayed portions of the plots. Fungicide application significantly reduced FLS severity and increased yield across all cultivars and years. Fungicide application reduced FLS severity proportionately to the susceptible of the cultivars (i.e. the greater the susceptibility the greater the reduction in disease with a fungicide application). Average yield saved with a fungicide application also increased as FLS susceptibility increased. Economic analysis on the profitability of a fungicide application based on cultivar selection will be discussed. Results based on this research support cultivar selection and appropriate fungicide applications are critical in minimizing the loss of yield due to FLS.

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