Thistles back after 20-year absence as herbicide spectrum shifts

Thistles have returned to Midwestern soybean fields after two decades of relative quiet, and the post-harvest window is the best moment to hit them, according to Steve Gauck, regional agronomy manager for Beck's.

"This is the best time to start taking notes on where you'll need a fall burndown," Gauck said. "And it's the best time to control biennial weeds like thistles."

The driver behind the comeback is a shift in herbicide programmes. As growers prioritised other weeds, products targeting thistles faded, allowing the weed spectrum to drift. "These shifts in herbicides are ultimately changing the weed spectrum," Gauck said. "And now, we're seeing thistles make a comeback after 20 years."

The damage is visible even after in-season measures. In Beck's Soybean Watch field south of Indianapolis, thistle patches left neighbouring plants with widely spaced nodes and a noticeably lower pod load.

What does a fall burndown change?

Once harvest wraps, the next decision is whether to settle for a contact kill or chase the taproot. Residual herbicides give longer control and matter most where thistles and other biennials built up pressure this season.

"Do you want to just kill what's up above the ground, or do you want to target that taproot?" Gauck asked. "The best time to control these weeds is in the fall. Take advantage of this timing to set next year's crop up for success."

Temperature is the limiting factor. Sprays need night-time readings above 50°F (10°C) for the chemistry to work. Northern growers can expect a tighter window than southern Indiana or Illinois.

Illinois: Red crown rot trials end, cyclobutrifluram sets the standard

Beck's in-season red crown rot (RCR) trials wrapped with a clear winner in the seed-treatment slot. Cyclobutrifluram delivered exceptional suppression and now defines the bar for RCR management, Matt Montgomery, Beck's agronomy education lead, reported. Other succinate dehydrogenase inhibitor (SDHI) actives produced less-than-ideal control, so product choice inside the SDHI family matters.

Seed treatment now sits alongside varietal tolerance as a critical RCR management layer. RCR keeps spreading across Illinois and will stay a planning factor for 2027.

Other 2027 watch-points from Illinois:

• Diversify soybean cyst nematode management with Peking varieties plus seed treatments
• Reassess fungicide return on investment
• Confirm adequate weed control plans
• Trial micronutrient packages

Early yield reports were positive, but a brutal end to August, with temperatures running 90–100°F (32–38°C), left upper-canopy pods unfilled on some fields. Heat stress also produced odd observations: pods sprouting beans inside the shell, green stems and an unusual number of purple stems in "stay-green" fields, where late rain appears to have restarted photosynthate production with too few pods left to receive it.

Iowa: SDS hits 5–10% of yield south of I-80

Beck's field agronomist Nate Meyer logged a difficult year for sudden death syndrome (SDS) in southwest Iowa. The disease favours wet, cool early-season conditions and showed up widely once August turned wet, with major outbreaks south of the Interstate 80 corridor. Some growers who had never seen SDS encountered it at high levels this season, and Meyer expects 5–10% yield losses in affected fields.

Earlier-season notes from Iowa:

• Many fields planted May 15–30 after cold, wet conditions delayed emergence
• Replant finished in some pockets into early June after hail and excess rain
• Timely mid-summer rains pushed plants taller than usual, triggering lodging
• Soybean gall midge on the western edge of the territory; septoria brown spot and cercospora leaf blight in pockets

Harvest was stalled by heavy September rainfall that Meyer ranked among the possible top-10 wettest Septembers on record. Combines will roll as soon as fields dry.

Minnesota: 7–9 inches of rain in 24 hours pauses harvest

Dale Viktora, Beck's field agronomist for Minnesota, reported single-day rainfall totals of 7–9 inches (180–230 mm) across parts of the state in the past week. The deluge evened out crop maturity across relative maturity groups, meaning most fields will be ready at once when sunshine returns.

Early yield reports were encouraging, with growers calling results better than expected, though Viktora wants more data before drawing conclusions. The 2026 season in Minnesota came down to rainfall geography: timely planting dates, limited foliar disease pressure, abundant sunny days and adequate rainfall combined to produce 75–80-bushel soybeans in the best pockets.

What farmers should watch next

Apply residual fall burndown while nights stay above 50°F, build RCR and SDS management around varietal tolerance plus targeted seed treatments, and prepare for a compressed harvest window if September rainfall carries into October.