Effects of Disease Resistance and Fungicide Application on Management of Tar Spot on Corn in the North Central United States

Tar spot, caused by Phyllachora maydis, is the most significant disease of corn in the North Central United States. Elucidating an integrated management approach to protect grain yield is a high priority. The integration of tillage, hybrid, and fungicide application on tar spot severity, canopy greenness, and grain yield was assessed in Indiana in 2019, 2020, and 2021. A split-plot arrangement of two tillage treatments as main plots with factorial arrangement of subplots with three hybrids (tar spot susceptible and two partially resistant) and fungicide application (propiconazole + benzovindiflupyr + azoxystrobin) were evaluated. Furthermore, a multistate study comparing two hybrids (susceptible and partially resistant) and fungicide application (propiconazole + benzovindiflupyr + azoxystrobin) was conducted in Indiana, Michigan, and Wisconsin in 2020. This research demonstrates that partially resistant hybrids with a standardized area under the disease progress curve of 2.5 and 3.0 had significantly less tar spot than a susceptible hybrid with a standardized area under the disease progress curve of 10.1 and increased canopy greenness ratings of 48.1 and 51.5%, which were significantly higher than the susceptible hybrid at 13.0% at maturity. Tar spot severity was further reduced and canopy greenness increased with a fungicide application in the susceptible hybrid. These results suggest that partial resistance alone may be used to manage tar spot. Yields did not differ significantly across hybrids with or without a fungicide application. However, a general trend of preserved yield potential was observed in the treatments with fungicide, indicating that knowledge of genetics and yield potential will be necessary to achieve the greatest benefit from partially resistant hybrids and judicious fungicide applications.