Field-Scale Evaluation of Fungicide Timing for Corn Diseases and Yield in Indiana from 2019 to 2022

Tar spot ( Phyllachora maydis), gray leaf spot (GLS; Cercospora zeae-maydis), southern rust ( Puccinia polysora), and northern corn leaf blight ( Exserohilum turcicum) are foliar diseases that can significantly reduce corn ( Zea mays) yields in Indiana. The objective of these trials was to test different foliar fungicide products in field-scale-sized plots to provide more accurate, real-world data. The effect of foliar fungicides on disease severity when applied at different corn physiological growth stages was tested on 11 field-scale research trials across Indiana from 2019 to 2022. In northeastern Indiana, pyraclostrobin + metconazole applied at the silk (R1) growth stage reduced GLS severity by 87.0% compared with the nontreated control (NTC). In east central Indiana, prothioconazole + trifloxystrobin applied at the 6-leaf vegetative (V6) growth stage reduced GLS severity by 65.8% compared with the NTC. In southern Indiana, flutriafol + bixafen applied at R1 significantly reduced GLS severity by 71.2% compared with the NTC. At all locations, there were no differences between treatments for southern rust, tar spot, and northern corn leaf blight severity and no significant effect of application timing on yield due to low disease levels. Although yield benefits were not observed at any location, these trials can provide insight as to the most appropriate timing to apply a fungicide if environmental conditions are conducive for disease development.