Tackling 2025 Soybean Diseases (Download PDF Version Here)

By Craig Allaman, Lead Agronomist at Cornelius Seed

 

Let’s to dive into the nitty-gritty of three soybean diseases that can hit your yields hard: Sudden Death Syndrome (SDS), Brown Stem Rot (BSR), and Red Crown Rot (RCR). These are no small players, and if you’re growing soybeans, you’ve likely run into at least one of them or you will. Let’s break down what we’re dealing with, how to spot them, and what we can do to keep these pests from tanking your season. I’ll also share some insights from a recent presentation I gave, plus the latest on a game-changing tool we’re eyeing for 2026.

 

Sudden Death Syndrome: The Silent Yield Killer

SDS, caused by *Fusarium virguliforme*, is a root disease that sneaks up on you. It’s been a headache since the ‘70s, and in my opinion, it’s the top soybean disease to watch in most of our growing regions. You’ll see it in patches, especially in low-lying, wetter areas of the field, and it can slash yields by 50% or more—sometimes up to 80% in bad cases. Last year, I saw it wreak havoc in east-central Iowa, with those classic symptoms: interveinal chlorosis (yellowing) and necrosis (browning) on upper leaves, veins staying green, and leaves dropping while petioles hang on like stubborn ghosts.

Here’s the kicker: to confirm SDS, you’ve got to get your hands dirty. Split the stem, and you’ll see a white, healthy pith—unlike the vascular tissue, which turns brownish at the roots. That discoloration, sometimes with blue fungal growth on the root surface, screams SDS. It loves cool, wet soils at planting (below 60°F) and hits hardest after heavy rains in July or August. Soybean cyst nematode (SCN) makes it worse, so if you’ve got SCN, you’re rolling the dice with SDS.

Management Tip: Plant varieties that have a high tolerance score and manage SCN. Delay planting until soils warm up and improve drainage where you can. Apply seed treatments like Profit Guard Plus, but I’m excited about a new Syngenta product, TYMIRIUM^® (pending registration). In trials, it’s shown SDS control as good as our go-to, Saltro, while also tackling SCN like a champ. More on that later.

 

Brown Stem Rot: The Northern Nemesis

Brown Stem Rot, caused by *Cadophora gregata*, is a big deal in northern soybean states like Iowa, Wisconsin, and Minnesota. It’s a vascular disease, not a root rot like SDS, and it can cut yields by 5-15% even in plants that look fine, or up to 38% when it’s bad. You’ll spot it mid-to-late season (R3-R5), often in compacted or low-pH soils. Foliar symptoms, if they show, look a lot like SDS interveinal yellowing and browning but the real tell is in the stem. Split it open, and the pith is brown, like pencil lead, especially at the nodes. No root rot, no blue fuzz.

BSR loves cool, moist conditions (60-80°F) and thrives in short rotations or no-till fields where soybean residue lingers. It’s sneaky because you might not see foliar symptoms, especially with the milder Type B strain, but yield takes a hit regardless.

Management Tip: Go for BSR-resistant varieties with Rbs genes (like Rbs1 or Rbs2). Rotate with corn or small grains for 2-3 years to break the cycle, and consider tillage to bury residue in no-till systems. Keep soil pH above 6.3 and fertility balanced. Seed treatments don’t help much here, so focus on scouting and resistance.

 

Red Crown Rot: The Southern Up-and-Comer

Now, Red Crown Rot, caused by *Calonectria ilicicola*, is newer to the Midwest but a growing concern, especially in southern Illinois—shoutout to my buddy Dave Smith, who’s dealing with it south of Jacksonville, IL. This disease is brutal, with yield losses up to 80% in severe cases. Dave told me some fields lost 30 bushels per acre last year! It’s more common in peanut-soybean rotations down south, but it’s creeping north, showing up in Illinois, Kentucky, and Missouri.

Look for red-purple discoloration on the lower stem and crown, with gray pith in the taproot. Under wet conditions, you’ll see white hyphae and those telltale brick-red perithecia—tiny balls on the crown or roots. Foliar symptoms mimic SDS: yellowing, necrosis, and early senescence. It loves warm, wet soils (77-86°F) and spreads through soil or equipment.

Management Tip: No resistant varieties yet, but we’re testing lines like PI 437970 for tolerance. Rotate with non-hosts for 2+ years, avoid peanuts, and clean equipment to stop the spread. Seed treatments like cyprodinil + fludioxonil show promise, and TYMIRIUM^® could be a game-changer here too, with strong RCR control in trials.

 

The TYMIRIUM^®Game-Changer

Let’s talk about TYMIRIUM^®, the Syngenta compound I mentioned earlier. Originally developed as a nematicide in the SDHI fungicide family, it’s a total rockstar. It controls *every* nematode we’ve tested, including SCN, which is a nightmare for soybeans. But here’s the bonus: it matches Saltro for SDS control and shows serious promise against RCR. Plus, it handles early-season diseases like frogeye leaf spot and Septoria brown spot. I saw it in action last year at a Syngenta trial in southern Illinois, and let me tell you, it’s impressive. If it gets registered for 2026, it could be a one-stop shop for every acre battling these diseases.

Scouting and Diagnosis: Get Out There

You’ve got to scout. SDS, BSR, and RCR can look alike with their foliar symptoms, so don’t guess—split those stems. For SDS, look for white pith and brown vascular tissue at the roots. For BSR, it’s brown pith through the stem. For RCR, check for red perithecia and crown discoloration. I was out in a plot last night, and we saw both SDS and BSR in the same plants—crazy, right? Send samples to a lab if you’re unsure; DNA tests or fungal isolation can confirm.

This year, I skipped my usual Saltro treatment for a planter box experiment, and now my fields are screaming with SDS. Lesson learned: don’t skimp on proven tools. Start scouting in mid-August, especially after wet spells, and focus on low spots or high-yield fields.

Wrapping It Up

These diseases—SDS, BSR, and RCR—are tough customers, but we’re tougher. Use resistant varieties, rotate crops, manage soil health, and lean on seed treatments where they work. Keep an eye on TYMIRIUM^®; it could change the game for SDS and RCR, especially in SCN-heavy fields. And don’t just sit there—get out, scout, and split those stems. Your yields depend on it.

Got questions or seeing these diseases in your fields? Drop me a line or tag me on X @CraigAgronomy. I’m always happy to talk agronomics. Let’s keep those soybeans thriving!