Southern rust emerge as the leading corn disease of 2025
As reported on the OMAFRA website fieldcropnews.com, as well as in previous articles by Farms.com, the 2025 growing season is nearing its end with corn and soybean farmers in Ontario and the U.S. Corn Belt facing disease challenges that reflect changing weather conditions.
For corn, two diseases have received the most attention—tar spot and southern rust. Tar spot detections began in early July, following patterns from previous years. The disease is firmly established across southwestern Ontario, from Essex to Niagara, and is spreading north toward Toronto. Hotter, drier conditions earlier in the summer kept tar spot levels low, but late-season humidity has triggered new outbreaks. Fortunately, this resurgence, along with fungicide use, is expected to limit yield losses compared to past years.
Southern rust, however, has emerged as the leading corn disease of 2025. Warm, humid conditions across the U.S. Midwest provided ideal conditions for its spread, and higher disease pressure has also reached southwestern Ontario. Test plot research shows that fungicide applications help reduce severity, but the full impact is still being evaluated.
Soybeans have also faced disease issues this season. Sudden death syndrome and soybean cyst nematode (SCN) have been noticeable in many fields. Fall is the best time for farmers to test soils for SCN while also preparing next year’s fertilizer plans. Sampling now helps identify yield losses and supports variety selection for 2026 planting.
Adding to management tools, the Crop Protection Network has launched a new Crop Disease Forecasting Tool. This web-based system provides daily updates and 7-day forecasts for major corn and soybean diseases. It now also includes risk assessment for Gibberella ear rot and DON, helping farmers make timely fungicide decisions and manage food safety risks.
With changing weather and increasing disease pressure, growers are encouraged to plan ahead, scout fields regularly, and use resistant varieties where possible.
For more information about the soybean cyst nematode, please visit the Farms.com Field Guide Pest pages.
Photo Credit: istock-urpspoteko