Tar Spot, Southern Rust and What Comes Next

On the latest episode of IL Corn TV, host John Klemm welcomes Ryan Gentle, Agronomy Manager with Wyffels Hybrids, for a wide-ranging discussion on what 2025 taught Illinois corn farmers and how those lessons should shape decisions heading into 2026.

Gentle, who covers the western half of Illinois from Galena to St. Louis, saw firsthand how dramatically different disease pressures impacted yields across the state. North of I-80, late-season tar spot and crown rot thrived after timely rains, with some fields seeing significant yield losses when fungicide timing didn’t align with disease onset. In some cases, growers who adjusted timing or made a second application saw 20–50 bushel differences.

Farther south, southern rust proved to be the bigger challenge arriving late and spreading rapidly. With a shorter disease cycle than tar spot, southern rust caught some growers off guard, leading to notable yield hits where fungicide strategies weren’t aggressive enough.

As farmers make hybrid and management decisions for 2026, Gentle cautions against reacting to a single year. “Look at multiple years of data,” he advises. Hybrids that excel against southern rust may not be the same ones that perform best in a tar spot year.

Beyond disease pressure, soil moisture is top of mind. Much of Illinois entered winter with significant subsoil moisture deficits. Gentle encourages growers to monitor soil conditions closely this spring, especially when evaluating planting windows.

For those using conservation practices like cover crops or strip-till, he recommends patience and awareness. Terminating cover crops ahead of planting, allowing soils to warm adequately, and avoiding sidewall compaction can help prevent early-season setbacks. He also reminds growers to scout for cutworm and armyworm, particularly in fields with heavy residue or winter annuals.

The key takeaway? Don’t abandon proven evaluation methods, just understand how changing conditions and management practices may shift your optimal timing.

Watch the full episode for deeper insights into disease management, planting strategy and protecting yield potential in 2026.

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