2025 Growing Season: A Challenging Year for Foliar Diseases (Download PDF Here)

By Craig Allaman, Lead Agronomist at Cornelius Seed

Well, folks, the 2025 growing season has been a wild ride for foliar diseases. It’s been a rampant year, with conditions that turned our fields into what felt like a Petri dish for disease. Let me break down what we’ve seen out there and what it means for our crops.

Southern Rust: A Heavy Hitter
Southern rust has been the talk of the season, and for good reason. When you see it coating leaf sheaths, you know it’s thick out there. This year’s outbreak was intense, but there’s a silver lining: we’re getting some fantastic data on hybrid tolerance. We’ll have clear ratings on which hybrids hold up well against southern rust and which ones struggle. This will be a game-changer for planning next season’s plantings.

 

Physoderma Brown Spot: A Minor Player

Physoderma brown spot showed up in small amounts, mostly in our show trial. This disease typically hits between V5 and V9, thriving in wet conditions where spores splash into the whorl. Thankfully, we didn’t have the kind of early-season weather that fuels this disease, so it stayed minimal. Just a blip on the radar compared to other issues.

 

 

Smut: A Frustrating Foe
Smut was a bigger headache this year, especially in my sweet corn plot. I made the mistake of planting it on the edge of a field next to a hayfield—a deer highway. Every night, those deer would take a bite out of the ears, leaving wounds that were perfect entry points for smut. I’d estimate 50% of the ears in that plot were affected, which made harvesting enough to freeze a real chore. Smut thrives on wounds, whether from deer, wind, or hail, and we had plenty of those this year with all the wind events tearing up leaves.

A Disease Hotspot Along the Mississippi
When I was out collecting tissue samples, it was like walking through a disease showcase. Tar spot, gray leaf spot, southern rust—you name it, it was there. I’d already sprayed fungicide, but the diseases were so entrenched by then that it was tough to keep up. The Mississippi River corridor was a hotbed for disease this year, with conditions spreading it in every direction. Further out from the river, things were a bit more scattered and less severe, but it was still a challenging season.

Looking Ahead
This year’s been a tough one, but it’s also a learning opportunity. The data we’re collecting on hybrid tolerance to southern rust will help us make smarter choices moving forward. Smut taught me a lesson about plot placement—next year, I’ll be rethinking where I plant my sweet corn to keep those deer at bay. And while Physoderma stayed quiet, we’ll keep an eye on early-season conditions to stay ahead of it.

Stay vigilant, keep scouting, and let’s use this year’s challenges to grow smarter in 2026.