Farmers in some areas of the state are harvesting green "stemmy" soybeans this fall. The stems are tough and still green, although the pods are mature and dry and ready to be harvested. It's not all fields that have this "Green Stem Syndrome," but there are some. "We've been fielding questions and listening to some frustrated farmers," says Clarke McGrath, Iowa State University Extension field agronomist in western Iowa. McGrath writes the "Corn-Soybean Insight" column each month in Wallaces Farmer magazine. "Questions, concerns and frustrations are ramping up."
Harvesting green, stemmy 50-plus bushels per acre beans is frustrating. "Grinding through them with a $350,000 combine when they are yielding in the 20s and 30s is excruciating at best. Sort of like watching a KC Chiefs game only longer," he says.
Green Stem in Soybeans—symptoms, causes and bad news about management
In some situations McGrath has seen plants with mature pods on green stems. The petioles can be on or off, he's seen both of these symptoms in fields this year. He's also seen fields where the plants have few to no pods on the upper nodes. The leaves are still on the plants at the upper nodes in some spots in the field, and immature green pods are clustered on the upper plant in other places in the field.
Sometimes there's only a bean or two in the pods, sometimes there are empty pods, sometimes the pods are twisted and opened up.
Season-long soil moisture stress seems to be a trigger, especially after the plants have flowered, says McGrath. When a soybean plant is growing normally at the beginning of the season, it produces high levels of carbohydrates to feed itself; when drought or other stress hits, pods can fall off or not fill in relation to the carbohydrate pool in the plant. So, the plant has a pool of reserved carbs and may stay green longer. "That is our theory anyway," he says. "It is sort of like an otherwise healthy corn plant that doesn't make an ear for some reason -- the plant often turns purple from the anthocyanin levels."
Weather conditions for fast dry-down of grain, but not enough time for stems to dry
Lower fall humidity and higher fall temperatures can also contribute to this green soybean stem syndrome; you get conditions for fast dry-down for the grain, but not enough time for the stems to dry.