Soybean growers have been calling Ben Pieper the past couple of weeks, telling him how tough their bean crop is to cut this harvest. The problem many are citing – green stem syndrome.
“I’ll have somebody in Iowa tell me that ‘these are the best beans I’ve ever had on the farm, and they cut beautifully, and are absolutely phenomenal,’” says Pieper, an agronomist for Merschman Seeds. “Then, with the same exact bean two hours to the east, the growers are dissatisfied with them, saying they cut hard, and aren’t yielding quite as high as maybe a different bean that we have in the lineup.”
University of Minnesota Extension notes green stem syndrome is a tricky issue for agronomists and growers to address, as the exact cause is unknown. That makes the problem difficult to prevent or address effectively in-season, and impacts harvest decisions.
Taylor Dill says the disorder contributes to a delay in crop senescence (maturation) of plant stems while pods and seeds mature and ripen normally – a so-called “source to sink” issue in the plant.
How this problem develops: Stems and leaves (the sources) typically send nutrients to the pods and beans (the sinks). But when stress reduces pod or bean development or causes them to abort, the nutrients and moisture get stuck in the stems and don’t get allocated well. That keeps the stems green even after the beans are ready to harvest, explains Dill, a PhD student at Ohio State University, in a video.
Two Basic Options For Soybean Harvest
While green stem syndrome might not contribute to direct yield losses, harvesting affected soybeans turns into a slow, hard slog for growers, contributing to increased fuel and harvesting equipment maintenance costs.
Farmers with fields impacted by the syndrome have two basic options at harvest, according to Shaun Casteel, Purdue Extension soybean specialist, on the latest episode of the Purdue Crop Chat podcast.
One option is to go ahead and harvest the beans when the grain quality is likely at at its best.
The downside, says Casteel, “We have the nasty combination of around 9% to 10% moisture in beans with green stems and have to slow down the harvest.”
The tough going in fields means you’re likely to use more fuel and put extra wear and tear on the combine.
Your second option is to wait until a freeze and the stems turn brown before harvesting. The downside? You might lose a fair amount of yield.
“I’ve seen this week where we had some early beans where the pods are opening up and the seeds just shattered,” Casteel says. “It’s just a mechanism of survival because [the pod is] trying to save itself. If your fields weren’t ready yet, that’s probably not going to be the case, but if we catch another cycle of rain, or we get into these two to three cycles of wet-dry, wet-dry, that pod really gets to the point of shattering in the field before the combine even gets there.”
Mark Licht, Extension cropping systems specialist at Iowa State University encourages growers to harvest when soybeans have a good moisture content, despite the tough conditions.
“Make sure the sickle bar on the combine is sharp and well-maintained,” he says, in an online article. “Slower harvest speeds will be needed to account for more soybean biomass coming through the combine.”
A poll by Reuters estimated 58% of U.S. soybeans had been harvested as of Sunday, Oct. 12.
What Factors Contributed To The Syndrome This Season?
Pieper, citing University of Minnesota research, says there are a lot of theories about the causal effects of green stem syndrome — everything from plant viruses, low soil moisture, and potassium deficiency, to high plant populations, genetic mutations and insect damage.
He says he believes many of those issues are factors and that heavy stink bug feeding has been another significant contributor to the problem this year.
“There is a crap ton of stink bugs and grasshoppers and insects in the chaff,” says Pieper who has observed the pests’ impact on soybean crops while doing yield checks.
Environmental stressors, drought in particular, were another contributing factor this season in Ohio soybeans, adds Dill.
Farmers often ask agronomists whether fungicide use is involved in the development of green stem syndrome.
Ohio State Extension reports certain modes of action can have a “stay green” effect on soybeans that can delay senescence and can be confused or contribute to green stem.
Pieper and his colleagues might be on the fence with that finding. They note in their podcast, Cup Of Joe, that fungicides contributed to soybean yield benefits this year – especially on marginal ground – with increases of 7 to 10 bushels per acre in some cases.
Bottom line, there are conflicting views regarding the role of fungicides in the disorder and more research is needed to pin down a definitive answer.
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