By Rebecca Vittetoe and Alison Robertson
Overall disease pressure for the 2026 growing season has been relatively low, especially compared to the southern rust outbreak we experienced last growing season. Gray leaf spot, northern corn leaf blight, bacterial leaf streak, Curvularia leaf spot, southern rust, tar spot, Goss’s wilt and Physoderma brown spot have all been observed in corn fields across Iowa this growing season. However, no one disease has become particularly severe and threatened yields so far.
In fungicide trials across the state, disease severity on the ear leaf has averaged less than 2% so far, this growing season. When disease severity at R5 (dent) is greater than 5%, a positive return on investment for fungicide application is likely. Despite periods of high humidity and extended leaf wetness, the yo-yoing of temperatures has likely helped slow a specific disease from really taking off.
With the recent wet conditions there have been concerns raised about late-season disease development and potential management considerations. Since we don’t have a crystal ball on exactly what the weather will bring in the next few weeks before maturity, it is difficult to predict what disease may become more prevalent.
Source : iastate.edu