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Got green soybeans? You're not alone

Agriculture.com Staff 10/07/2010 @ 9:46am

The 2010 soybean harvest looks promising for Illinois growers with early yield reports indicating the best harvest many growers have ever seen. However, green soybean plants and stems may reduce harvest speed this fall.

Vince Davis, University of Illinois Extension soybean specialist, says the biggest issue concerning growers this fall continues to be green stems and green plants that remain in fields that are otherwise ready to harvest.

“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 says in a university report. “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.”

Entire plants that remain green can easily persist until a killing frost occurs, he said. These cases can also range from entirely genetic to entirely environmental causes.

“Genetic causes in nature are due to male sterility, causing plants to set about 85 percent fewer pods resulting in 4.5 times greater carbohydrate concentrations in the root, stem, and leaf matter,” he says. “In 2006, Curtis Hill and fellow researchers evaluated 1,187 different MGI and MGII cultivars in Illinois from 2001 to 2004 and found some relationships between percentages of green stem to certain cultivars suggesting better variety selection may be possible.”

Unfortunately, the syndrome is elusive under different environments, and 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 adds. “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 says it’s difficult to pinpoint the culprit when scouting at the end of the season.

“The good news is that these issues tend to appear in fields with average to high yields,” Davis says. “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 much these green plants and stems reduce harvest speed.”

In most cases, the percentage of green plants is 1 percent or less of the field. Harvest speed is not affected greatly at those levels when harvest conditions are dry. In severe cases where green plants can be 10 percent or greater, harvest speed can certainly be reduced, Davis says.

No clear answers exist for why these symptoms appear, and little can be done about it. In severe cases with high percentages of green plants, delaying harvest until after a killing frost might be an option, but monitor the weather and the integrity of the other plants so you don’t lose yield to lodging or shattering.

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