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Corn+Soybean Digest

Green Stem Still a Mystery

There's a soybean disorder — makes fuel vamoose.

Why, Green Stem's a bit like the Grinch from Doc Seuss!

Ripe pods on green stems in the combining season?

Now, please don't ask why. No one quite knows the reason.

It could be the weather or bugs or a blight,

It could be, perhaps, the variety's not right.

They'll clog up your combine, slow work to a crawl,

Your patience, you'll find, is two sizes too small.

Green stem is a mysterious malady that causes soybean stems to stay green and moist after the pods and seeds are fully ripe. It doesn't happen every season, but when it does, “it's a real aggravation,” says John Hill, Iowa State University plant pathologist. It slows down the combine, eats up diesel fuel and sorely tries your patience, turning harvest into a “grinchly” grind.

“It's really frustrating when you have to get out of the cab every 15 minutes because the stems are wrapping around the reel,” says Cedar Rapids, IA, farmer Lance Lefebure. He shot a video of his revved-up combine chewing through green stem soybeans and posted it on YouTube, where over 1,000 viewers have witnessed his vexations (

THE SOYBEAN DISORDER has been observed for decades, but there are reports that it's becoming more common. “Green stem was first reported in 1974, but it was relatively unheard of until the last 10 years,” says Dennis Epplin, a University of Illinois Extension agronomist. Why it might be increasing is a mystery, because the cause of green stem is unknown.

Various culprits have been proposed, says Glen Hartman, a plant pathologist at the National Soybean Research Center. Environmental stresses such as drought, viruses and insect damage are often - but not always - associated with green stem, he says. “We haven't pinpointed the environmental factors.” As so often happens in agriculture, Epplin says, “we may find there's more than one thing going on at once.”

Bill Pearce, who has been farming for 47 years in Franklin County, IL, has seen green stem fairly often in the past decade. On his farm, it seems to be linked to fluctuating soil moisture, he observes. In 2007, all his soybean fields were affected. The crop was stressed by a long, hot, dry period after flowering, followed by a rainy period, which rejuvenated the leaves and stems. The pods matured early, but the stems never did turn brown. Yields were 25% lower than usual, too, he says.

Green stem doesn't necessarily cut yields, Epplin says. But the disorder has been linked to reduced pod set - perhaps because “there are not as many seeds to remobilize the nutrients from the stem and leaves. That's just a theory, though.”

At harvest, the beans “were very hard to get through,” Pearce says. He slowed his ground speed by one-third in order to slice through the tough, pliable stems, while keeping the engine speed high. That lowered fuel efficiency. Harvesting green stem soybeans can double or even triple your normal fuel consumption, Hartman says. “That comes right out of your pocket.”

This is a problem that “both breeders and growers would like to solve,” Epplin says.

But meanwhile, your only defense is variety selection, Hartman says.

University of Illinois variety trials show that cultivars consistently differ in their susceptibility to the disorder. You can find green stem sensitivity ratings for hundreds of varieties on the Variety Information Program for Soybeans (VIPS) Web site.

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