By KAREN BINDER
Illinois Correspondent

URBANA, Ill. — Sure, this year’s soybean harvest in Illinois will be one of the best, but not without slowing down some farmers first, thanks to Green Stem Syndrome.

University of Illinois extension specialists have been receiving troubling reports of green soybean plants and stems statewide. Often called Green Stem Syndrome, this affliction causes soybeans to remain green until a killing frost. When farmers go to harvest the otherwise dry plants, the green stems tend to wrap up in equipment, forcing them to slow down the harvest.

Vince Davis is an extension soybean specialist. He said this is the single biggest issue concerning growers this fall.

“Green stems, sometimes referred to as ‘green stem syndrome’ or ‘green stem disorder’ occur when stems remain green even though pods and seeds yield and mature fine,” Davis said. “The condition can range from a nearly normal number of pods on a plant with green stems, to entire plants that remain green with few pods and no seeds developed.”

The soybean harvest is on a fast track this year. The USDA-NASS crop report estimated 50 percent of the crop was harvested as of Oct. 4, and with good weather forecasted through the rest of the week, the rapid pace will continue. In the last 10 years, only 2007 moved faster, with 54 percent harvested at a similar date.

USDA officials say this will be the largest soybean yield average in history. Yet, green stem is a growing concern not only in Illinois, but also across the Midwest. “It’s a real aggravation,” said John Hill, Iowa State University plant pathologist. It slows down the combine, eats up diesel fuel and sorely tries one’s patience, turning harvest into a “grinchly” grind.

He added that growers are having to hop off their cabs frequently to unravel stems wrapped around the reel, but added there doesn’t appear to be any pattern to the incidence rate.

Dennis Epplin, an Illinois extension agronomist, mentioned the disorder has been observed for decades in all soybean-growing areas, beginning in 1974, but has become a recognized issue only in the last 10 years. He said it remains a mysterious condition with which to cope.

“Genetic causes in nature are due to male sterility, causing plants to set about 85 percent fewer pods, which results in 4.5 times greater carbohydrate concentrations in the root, stem and leaf matter,” Davis said.

There was research in 2006 in which 1,187 different MGI and MGII cultivars in Illinois from 2001-04 were evaluated, that found some relationships between percentages of green stem to certain cultivars, suggesting better variety selection may be possible, Davis said. He warns, however, there is likely little information for growers to access to aid in their seed selection.

“While genetics may play a role, symptoms can also be environmental,” he added. “It is commonly associated with viral infections, primarily bean pod mottle virus and secondarily tobacco ringspot virus. It can also be caused by insects feeding on flowers. Stink bugs are a primary culprit, but bean leaf beetles and corn rootworm beetles are also suspects.”

In addition, other abiotic stress factors, such as drought, that increase flower abortion and cause pod loss can play a role. With the number of potential causes for this syndrome, Davis said it’s difficult to pinpoint the culprit when scouting at the end of the season.

But there is some good news. While it makes sense that individual less-productive plants reduce yield, green stem problems tend to appear in fields with average to high yields. One reason is that green stems are a sign of favorable growing conditions throughout the maturity of the other plants.

The only real concern for most growers is how many of these green plants and stems reduce harvest speed. In most cases, the green plants constitute no more than 1 percent of the field. Harvest speed is not too affected at such levels when harvest conditions are dry.

In some severe cases, where green plants are 10 percent or greater, harvest speed can certainly be reduced. Unfortunately, there are rarely clear answers between fields for why these symptoms appear, and little can be done even if the reason is evident.

In cases with high percentages of green plants, delaying harvest until after a killing frost might be an option. Entire plants that remain green can easily persist until a killing frost occurs, Davis said. These cases can also range from entirely genetic to entirely environmental causes.