Reports are trickling in about green stem syndrome, or GSS, occurring in Iowa soybean fields this fall, which is like rubbing salt in the 2013 soybean crop wound. "Before we get into details of the disorder, we wanted to let you know that the Iowa State University Extension IPM program is doing an analysis to determine the most common causes of GSS," says Daren Mueller, an ISU Extension plant pathologist.
In the following article, Mueller and ISU Extension field agronomist Clarke McGrath discuss the confusion about what actually causes this disorder. If you have a field with any level of GSS, Mueller and McGrath would like to include it in their analysis. Please contact Nate Bestor (email@example.com), Iowa State University pest management specialist, to see how you can participate.
What is Green stem syndrome? What are the symptoms?
Green stem syndrome (see photo accompanying this article) is a soybean disorder in which stems remain green after pods and seeds are fully mature and ready to harvest. Cutting affected plants during harvest is difficult and seed quality can be reduced.
There is a classic definition of how GSS appears, but in reality, the symptoms vary quite a bit. Sometimes, plants with GSS can have just a few pods on the upper nodes, or there can be leaves still on at upper nodes in some spots. Also, immature green pods may be clustered on the upper part of the plant, and even empty pods have been associated with GSS.
Bottom line: if there are any mature pods in a field ready to harvest, and green, chewy stems are also present—"this is considered GSS by our definition," says Mueller.