With 2025 harvest in full swing, soybean farmers across the Midwest and beyond are contending with a growing problem: green stem syndrome, a physiological disorder that leaves soybean stems stubbornly green long after pods have matured. While it doesn't directly affect yield, it poses major challenges at harvest and is prompting tough decisions in the field.

Ben Pieper, agronomist with Merschman Seeds, says he's been fielding calls from frustrated growers seeing inconsistent performance from soybean varieties - even across short distances.

"One farmer tells me they've got the best beans ever; two hours away with the same variety, another says they cut hard and yield lower," he explains.

The disorder results from a breakdown in nutrient flow, where the plant's resources remain trapped in the stems due to reduced pod fill or pod abortion, explains Taylor Dill, a Ph.D. student at Ohio State University. This causes delayed senescence, with stems staying green even after seed maturity.

Hard Choices at Harvest

Shaun Casteel, Purdue Extension soybean specialist, says farmers with affected fields face two difficult options: harvest now with tough, green stems or wait for a frost to kill the plant.

"Harvesting now means you're dealing with 9-10% moisture beans and green stems - slowing down the combine, increasing fuel use and wear," says Casteel.

"Wait too long, and you risk pod shatter and lost yield."

Mark Licht from Iowa State University advises farmers to harvest when seed moisture is good, even if stem conditions are poor.

"Keep the sickle bar sharp, and go slower - there's more biomass to manage," he says.

A Reuters poll indicated 58% of the U.S. soybean crop had been harvested by October 12, leaving many fields still at risk.

What's Causing Green Stem Syndrome in 2025?

Agronomists point to a complex mix of factors this year:

• Heavy insect pressure, particularly from stink bugs and grasshoppers

• Environmental stress, including persistent drought

• High plant populations and low soil potassium

• Fungicide effects that delay plant senescence

"There's a crap ton of stink bugs and grasshoppers in the chaff," Pieper says, based on recent field checks.

While some researchers question the role of fungicides, others note that certain formulations may unintentionally prolong greenness. Still, Pieper reports positive yield benefits from fungicide use in many fields this season - especially on marginal ground, where returns ranged from 7 to 10 bushels per acre.

Another layer of complexity is genetic. Some soybean varieties appear more susceptible to green stem syndrome than others, though more research is needed to fully understand the interactions between genotype, stress, and environmental triggers.

As the 2025 harvest progresses, growers are urged to monitor moisture, manage harvest speeds, and balance the trade-offs between crop quality, machine wear, and yield loss.

In a year marked by disease pressure, drought, and volatile commodity markets, green stem syndrome adds yet another variable to the U.S. soybean grower's equation.