By Alison Robertson
In 2025, the effect of commercial fungicides on foliar diseases of corn were evaluated at six ISU Research and Demonstration Farms: Northwest Research Farm (NWRF), Northern Research Farm (NRF), Northeast Research Farm (NERF), Armstrong Memorial Research Farm (lost due to wind damage before tasseling), Ag Engineering and Agronomy Farm (AEA), and Southeast Research Farm (SERF). Fungicide products evaluated and timing of application are shown in Table 1. A generic product applied at silking or at silking + ~21 days later (milk stage) was included to compare return on investment with name-brand products that are more expensive.
Southern rust was the most prevalent disease observed at all farms (Table 1), although tar spot, northern corn leaf blight, and bacterial leaf streak were also present at various locations (data not shown). Southern rust severity varied across locations and was least severe in central Iowa (7.8%) and most severe in southeast Iowa (50.0%).
Effect of fungicides on foliar disease.
All fungicides reduced southern rust. Among name brand products, efficacy varied slightly and no one product was consistently better than other products across locations. Two applications of the generic product, Cover XL, consistently reduced southern rust the best, although the reduction in southern rust severity was not always significantly different from name brand products. One application of Cover XL was not as effective at reducing southern rust as two applications of Cover XL, but it was not less effective than some name brand products.
Source : iastate.edu