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Unusual malady hits soybeans

Researchers are hard at work looking for the cause of an odd, late-season development in Arkansas soybean fields.

“There are plants in large areas that simply refuse to mature,” says John Rupe, plant pathologist with the University of Arkansas. “They remain green and have very few developed pods.”

Of the pods that are on the plants, many contain only one or two seeds. At the same time, there’s bud proliferation at the nodes.

In some cases, an entire field is affected. Most cases, however, involve just a portion of the field — “but it’s often a very large portion,” says Rupe, who toured affected fields the last week of October.

“Because the plants are staying green, they can’t be harvested. Growers are forced to harvest around them. So there are large green islands left out there. There’s still a lot to be discovered about why it’s happening.”

The mystery malady is “not an overwhelming thing statewide,” says Jeremy Ross, Arkansas Extension soybean specialist. “But it’s on the rise and where it is bad, operations are definitely being hurt. Losing 40 or 50 acres isn’t easy to ignore.”

Although there is no definitive proof stink bugs are the cause or vector for the current problem, the pest has been responsible for similar symptoms in the past, says Ross. Stink bugs have “come in late and fed on pods and plants stayed green until a heavy frost. Most of that was in the southern part of the state, though, and the current situation has moved north.”

Where the problem is occurring, “there are wildly varying degrees of trouble — up to 100 percent of the field can be affected,” says Scott Monfort, Arkansas Extension plant pathologist. “Some fields have a tiny amount of it and others are inundated. The tiny pods and plant configurations kind of make them look like a ‘witch’s broom.’

“Many of those fields have almost no pods worth harvesting. We were looking at one field where the farmer will be lucky to harvest 10 bushels per acre.”

From a distance, the lush fields make “you think the yield would be decent, at least. These are waist-high plants. But walk through them and there are very few pods.”

At the end of October, Prairie County, among the worst-affected areas, had harvested about 60 percent of its soybeans. In the past, the erratic problem would flare in “only 1 or 2 percent of the plants in a field,” says Hank Chaney, Prairie County Extension agent. “Now, though, we’re seeing numerous acres, or even entire fields, where plants aren’t slowing down or even showing signs they’re ready to mature. The magnitude of this is worrying. There are farmers right now who have significant amounts of their acres with these symptoms. It makes you scratch your head and wonder what’s going on.”

Chaney was recently alerted to two more fields (a 40-acre field, and 55 out of 80 acres in another) of “weird” soybeans that “look as green as a gourd and ready to keep going, like it’s the middle of July or August.

“We’ve had some cooler weather recently. Maybe that’ll knock some of those leaves off. I’ve seen a grower put out Gramoxone. It turns them black, but the leaves still hang onto the plant. It’s just strange.”

Is there a connection to a certain variety or maturity group?

“Not that we know of. We’ve looked at various things that might be connected to this and come up with nothing concrete. At first, we thought it might be hooked in with a particular seed lot or source. But it didn’t take long to find that wasn’t the case.”

The bright patches of green are “really striking,” says Chaney. “I don’t know if it was related to the weather. To be honest, this has been a really weird year — there were a lot of folks that couldn’t get rice to dry down and other things.”

And like Rupe, Chaney reports the beans on the plants are in “strange configurations and sizes. All the beans might be on one side of the plant. On other plants, the beans look like big, huge butterbeans.”

Why the huge beans? “Primarily, that’s probably due to there being so few beans on the plant,” says Rupe. “That’s allowed the plant to pump added nutrients to the few that are there.”

In the past, researchers trying to unlock the malady’s cause have searched for causative viruses and various pathogens. Nothing consistent has been found that would cause the symptoms.

“This time around, I hope we’ll find some things that will clue us in on how to approach it,” says Rupe. “One of the things we’ve done is send pictures of these fields and affected plants to county Extension agents and consultants all around the state — and this is also occurring in quite a few northeast Arkansas fields. We’re trying to get a feel for exactly how extensive the problem is.”


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