Soybean fields in southwest are presenting with green stem syndrome, according to Jill Scheidt, an agronomy specialist with University of Missouri Extension.

"Normally, when a soybean plant matures, it drops its leaves, and stems lose their green color," Scheidt said in a recent news release. "Soybean plants affected by green stem syndrome will not dry down properly, and seed may mature before the stem turns brown."

6 causes for green stem syndrome
There are many causes of green stem syndrome, Scheidt said. Here are six:

• viruses
• low soil moisture
• potassium deficiency
• soybean population density
• genetic mutations in soybean plants
• insect damage

STILL GREEN: Green stems in soybeans at harvest are not a good sign. Some southwest Missouri fields are showing symptoms of green stem syndrome. Still, University of Missouri agronomists say farmers should not delay harvest waiting for the plant to drop leaves. (Photo courtesy of Jill Scheidt)

Management options
Reduced pod number during the full seed stage is an associated cause; this is because carbohydrates and nitrogen remain in the stem and roots, and appear to have a role in retention of green stems.

"There were above-threshold levels of green stinkbug this year," Scheidt said.

When green stem syndrome is triggered by green stinkbug feeding, management of the insect may be helpful. Treatments must be applied when leaves and pods are green, and feeding is taking place.

"When green stem syndrome results from viral infection, management is difficult. Managing viruses usually requires controlling the vector of the virus," Scheidt added.

Don't delay harvest
According to Iowa State University, lower fall humidity and higher fall temperatures can be associated with green stem syndrome; they can lead to faster drydown for the grain, but not stems.

Scheidt does not recommend delaying harvest to allow green stems to dry sufficiently. "Delaying harvest by three to four weeks usually results in exceptionally low seed moistures, and increases shattering and harvest losses," she said. "So plants affected by green stem syndrome should still be harvested when soybeans reach 13% moisture, even if the stems are still green."

Note: The University of Missouri contributed to this article.